Putting a PT-65B switchmode power module into an Apple IIe

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Putting a PT-65B switchmode power module into an Apple IIe

Hi -

I finally managed to replace the power supply of my Apple IIe with a "Mean Well" PT-65B switchmode power supply. As you can see from the photo, it fits nicely into the metal box of the original power supply, and once the box is closed, no difference can be seen.  Here is the photo with the metal box still open:

 

 

The yellow circle is the new power supply module mounted in the original shell. Monitor shows "Wings of Fury" loaded from floppy disk and running fine. (Red arrow points at potentially bad original Apple 80 Column / 64 k RAM card, more on this later).

 

My IIe now has a much better power supply which will work worldwide, with any line voltage and frequency, unlike the original power supply which was for 220V (it's an Europe / PAL version Apple IIe "Made in Ireland").

 

If you are reading this and are interested in such an upgrade / replacement, I could write more about how it was done. There are no electrical issues, anyone could do that, but there are mechanical issues which need to be solved (and frankly, my first solution for that failed).

 

WHY TO REPLACE THE ORIGINAL POWER SUPPLY PCB COMPLETELY

 

You might ask why I did not attempt to repair the original power supply (only the usual culprit, the "Rifa" capacitor had exploded / cracked open). The reason, other than the 220V issue which limits the Apple IIe to my lab, where I have a step-up transformer, is that all the electrolytic capacitors in the original power supply are 40 years old, and beyond their safe life span. Which means they all need to be replaced to have a reliable power supply which would not cause more trouble down the road. And unlike some people believe, it is neither trivial nor cheap to replace the electrolytics in a switchmode power supply. They need to be chosen carefully to be suitable for this application, and "normal" electrolytics designed for filter purposes after an AC rectifier just won't do. These are specified for 120 Hz operation only, while the typical switchmode power supply works at more than 100 x that frequency. For electrolytics in switchmode power supplies, ESR at high frequencies (up to 100 kHz or more) and ripple current ratings at higher frequencies are critical, otherwise, they might just overheat and explode. So be warned, don't attempt to replace electrolytic capacitors in switchmode power supplies unless you are competent in this field of engineering. Now, the bad news is that suitable electrolytics are special types which are so expensive that replacing all of them would cost more than a brand new PT-65B. Besides the mechanical issue that none of the modern replacements have the same footprint anymore. Even electrolytics did shrink in size in the past 40 years. This mechanical complication is worse than you might think - the issue is how to bend the leads properly without damaging the seal of the rubber plug. It can be done, but then the next issue is how to prevent them from wobbling around, they need to be glued together somehow. Same reason why "Mean Well" puts white silicon goop in their power supplies to secure larger components, like electrolytics, in place. All this conspires against replacing these old electrolytics in the old power supply PCB. IMHO, it's simply not worth the time, money, and effort.

 

NEW POWER SUPPLY WORKS FINE ! BUT A CARD DOES NOT WORK !?

 

I've tested the new power supply together with a disk drive, and all works well. Alas, I found out that Broderbund's "Wings of Fury" game, which needs 128k of RAM, did refuse to work with the original Apple 80COL/64K Memory Expansion card (red arrow in photo). It terminates the load with the message that it needs a 128k machine to run. I have a Taiwanese clone of this card which works, and the game loads and runs with it. So there is no reason to suspect the new power supply.

 

IS THERE A GOOD WAY TO TEST THE CARD ?

 

If you have a hint how I could test the original Apple card for memory faults, let me know. I think there ought to be a way to do this with the built-in diagnostics-in-ROM, but my internet searches did only yield useless clutter, as I am not set up to make real floppy disks from images, so I can't load any diagnostics which float around in the web into my machine, except if they would be AIFF or WAF files for cassette interface load.

 

Oh, and please don't forget to comment if you want to know more about the PT-65B conversion.

 

- Uncle Bernie 

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Nice work!

I've done the same type of conversion for similar reasons, (In my case the PSUs had been previously worked on and I really didn't want to try and reverse engineer what the other person had done.)

Rebuilding Apple II Power Supplies – I Like 8 Bits

I'd like to see your take on this so put me as a +1 to showing uis the PT-65B conversion.

 

Cheers!

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Get XPS Diagnostics //e from

Get XPS Diagnostics //e from Asimov.  Run the memory test from that.

 

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And yes...  quite intersted

And yes...  quite intersted in the MeanWell power supply...  It should be significantly cheaper than other replacement power supply board options.

 

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Hi Uncle Bernie!

I'd like to know more too, I have an empty case from the original power supply. I was wondering how to use it better.

For your second question, I can recommend Apple //e Dealer Diagnostics. 

.Package iconApple IIe Diagnostic.zip

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How are you getting the -5V

How are you getting the -5V output?  Adding another regulator like an LM7905?  If so, which other output do you tap to get the power for it the +12V?

 

 

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softwarejanitor wrote:How are
softwarejanitor wrote:

How are you getting the -5V output?  Adding another regulator like an LM7905?  If so, which other output do you tap to get the power for it the +12V?

 

Yes, it needs a 7905 regulator to get -5V from the -12V.

(Exactly the same approach as the RPT 60B: https://www.applefritter.com/content/12v-power-supply-conversion-using-mean-well-rpt-60b)

 

Even though the PAL version of the Apple IIe only needs -5V for the cassette input op-amp, you don't want to omit it, because some cards might need it.

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inverter?

What are the pros/cons of using a linear LM7905 vs a charge-pump voltage inverter such as a ICL7660 or CAT660?

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There's a 10 to 1 increase in

There's a 10 to 1 increase in current drive availability with the 7905 (1 Amp) compared to the 100mA of the CAT660, but having 1 amp capability on the Apple II -5v rail is a bit of overkill.

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Yes there is a 7905 regulator involved !

In post #6, softwarejanitor wrote:

 

"How are you getting the -5V output?  Adding another regulator like an LM7905?  If so, which other output do you tap to get the power for it the +12V?"

 

Uncle Bernie answers:

 

The PT-65B makes -12V and so it's cheap to add a 7905 regulator to provide the regulated -5V rail for the Apple IIe. But exactly this is the "mechanical problem" I ran into and botched on my first attempt. I found a solution, though, but this might not be the preferred solution for all users.

 

You see, my goal was to really 'hide' the mod that no casual observer could find it out. It would have been very easy to just drill a hole into the front side wall of the power supply metal enclosure for the screw holding the 7905 in place (it should have a nice heat sink, just in case some random slot card is discovered which loads the -5V rail all too badly, not very likely to happen, buy why take chances when it can be done right). I used a TO-220 mounting kit sold by JAMECO to mount the 7905 in an isolated way. It comes with a mica sheet that goes between the 7905 and the metal enclosure (thin coat of thermal paste on both sides) and the screw itself goes through an insulating plastic insert for the mounting hole of the TO-220 package. A very nice solution which is hard to put together from individual components.

 

The mechanical problem came from my desire to avoid that visible screw on the front side of the power supply metal box. So I tried to mount the 7905 to the bottom of the box. I thought that I could just drill a hole and then chamfer it such that the screw head would be sunk and not stick out, preserving a perfectly flat bottom of the power supply. I did not want to drill a hole into the bottom part of enclosure of the Apple IIe itself, which would have allowed for the screw head to stick out.

 

But as it turned out, the chamfer, when deep enough to hide the screw head, weakened the sheet metal enough that when tightening the screw, its head just got pulled through the sheet metal, leaving a larger hole, and a loose 7905. Botched ! What a disaster ! Here is that hole (red circle):

 

 

Despite of this failure I insisted on mounting the 7905 on the bottom of the metal box. I would have hated to cut all the nice wiring and heat shrink tubing open to redo it again, with longer wires, to mount the 7905 on the front side of the metal box. Again, lesson learned: always do all the mechanical work before wiring anything up. Then, the attempt to tighten the screw would have had the same disastrous outcome, leaving this ugly and useless hole, but then I could have opted to mount the 7905 at the front side, with longer wires, and accepting that a small screw head would be visible. This is the way I'd recommend for anyone why wants to put such a PT-65B into an Apple IIe power supply shell. Form follows function. Not vice versa.

 

The nasty (and not recommended) solution I used to avoid rewiring of the 7905 was to mill a flat recess into the bottom of the box, just deep enough to sink most of the screw head, but not too deep to weaken the sheet metal too much. This was done with a mill bit in a drill press - which is not the right way to do it, because a drill press is not a milling machine (which I don't have). The bearings of drill presses are not designed to take any X Y forces caused by typical milling operations, but for just milling downwards (Z axis) they can take it without getting damaged. But there is some wobble which ain't no good, as the mill bit wants to rattlethe work piece away until fully engaged. It really sucks to have no machine tools like mills and lathes. On the other hand, how often would they be used ... not worth the investment for most hobbyists. The outcome was this:

 

 

Note how I took a file to the screw head, after the 7905 was installed, to flatten it down flush with the metal surface.

 

Again, this is not the best way to do it. I recommend to mount the 7905 on the front side of the power supply box. near the point where the cable bundle to the motherboard comes out. As I didn't do this in my case, sorry, I have no photos how that would look. Maybe if you do your power supply conversion the right way, mounting the 7905 on the front side (from the  inside  of the box of course), you can snap a photo and post it in this thread.

 

Other than that, the conversion is quite straightforward. The PT-65B  almost  fits into two of the the mounting standoffs for the original PCB, but not perfectly, so a little bit of filing a notch into the PT-65B PCB must be done, to allow the use of these original standoffs:

 

 

Sorry, I have no photo of the notch itself. It is hidden below the washer visible in the yellow circle. Just be patient and slowly file the notch, as the red outline suggests, with a round file, until the PT-65B  can be put onto these two standoffs. The one on the other side of course uses the screw hole on the PT-65B itself. Two washers are recommended (one below, one above) to avoid cracking the PCB. Be gentle when screwing on the nut (not installed yet in the above photo). The nuts from the original PCB mount may be reused, but I did not find a proper socket fitting to them. This solution has adequate mechanical strength, because the other two standoffs for the PT-65B are tailor made: the required holes are marked on the sheet metal, by using the PT-65B as a template for the holes.

 

The technique I used is to mount nylon standoffs (machine screws work, too) into the two remaining mounting holes of the PT-65B, and then I put some paint in their tips. Mount the PT-65 onto the existing two standoffs and make the tips touch the sheet metal, where they leave some paint points. These are the locations to drill the holes. After removing the PT-65B out of the danger zone, drill the two holes with a drill press, but drill a little bit larger than the screw diameter, to have some leeway for inaccuracies. Then use a tool with a domed tip and a hammer to drive the sheet metal in from the bottom side, just enough that the flat screw heads of #6-32 flat head machine screws (length  3/4") are flush with the metal surface. This tool can be improvised by using a ball bearing steel ball glued onto a steel tube of slightly smaller diameter than the ball. Nylon standoffs are put into a small machine vise and taken to the drill press to hollow one end out, such that it sits snug on the metal domes / eyes, see this photo:

 

 

Afterwards, the nylon standoffs are cut to the right length with a saw. The proper height is the same as for the exisiting metal standoffs.

 

Next step is to install a new AC connector. This is necessary because the original connector is soldered into the PCB of the old power supply:

 

 

The important thing here is to find a connector which fits into the existing cutout. I can look up the type number of the one I used, but not right now.

Also note the bending trick which was used to be able to drill the screw holes from behind, with the connector heat glued in place. This bending can only be done once. If you prefer to avoid bending the sheet metal, you can drill these holes from the front, but getting them in the right place requires more measurements, maybe a template, and if you screw that up, and the holes are off position, the connector will sit with an ugly slant or could not be installed at all. I prefer to use the mounting holes of the connector as a template / guide for the drill bit.

 

The PT-65B is mounted using flat washers with star washers on top of the flat washers on the PCB solder side, and flat washers on the component side. The nuts are #6 nuts. You could use the ones left over from the original PCB, but these are smaller and I had no proper socket fitting them.

 

 

The above photo shows the situation before the star washers are put on. Then comes the PT-65B PCB, then another set of four flat washers, then the nuts. Star washers will make good electrical contact with the "ground" islands around the mounting holes of the PCB. This is an important electrical safety feature. Use the prescribed washer sequence. Do not overtighten the nuts. Just tighten them with reasonable finger force until snug, and then tighten another 90 degrees turn, not more.

 

You can see now that the mechanical work of this power supply conversion is the most difficult part, and requires a drill press and some small tools not available in a typical household tool box. The electrical wiring as such is almost child's play. After the original cable has been desoldered from the PCB, a new 6 contact MOLEX connector is installed while adding the two extra wires (from V3 = -12V and COM on the PT-65B) to the 7905.

 

Here are a few photos showing the wiring:

 

 

(You would use longer wires to the 7905, so it can be mounted on the front side of the metal box)

 

Here is the line voltage side wiring:

 

 

Note that there are two green / yellow ground wires, one goes from the AC connector to the bolt on the right side, and one from the AC connector to the ground tab on the PT-65B.

 

And here is the final result:

 

 

Don't forget to fasten the ground connection nut, in the above photos it's still loose for a reason (some conductivity tests I wanted to do before powering it up - the PT-65B has its own ground contacts on the PCB, and I wanted to measure the resistance they have to the sheet metal).

 

For the power requirements of an Apple IIe system, the smaller and cheaper PT-45B would do. It is built on the same PCB as the PT-65B, but uses lower profile components. All electrical connections and the mounting hole placements are the same.

 

So much for today's internet session. I have much more photos and information, but now you have the basic ideas how it was done. If you like it, and want to do it yourself, I can provide more info. Just encourage me with comments (and questions you might have).

 

- Uncle Bernie

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Nice!  That power supply is

Nice!  That power supply is quite readily available and inexpensive.  The mod looks easy to do.  Pretty nearly perfect.  Definately a great way to go.

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That's a very neat job

Well done UncleBernie.

There's definitely some tips and tricks you used that I will keep in mind for my next rebuild.

 

Chesh

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I was just digging through my

I was just digging through my parts stash...  I have 3 power supplies right off hand that need to be fixed...  one Apple supply of the Dynacomp variety common to Platinum //e, one AE supply and one Franklin supply.  I think this Mean Well PT-65B method can be adapted to all three of them.  I think I will order some PT-65B boards and I am pretty sure I've got plenty of LM7905 on hand already.  I was probably going to put Reactive Micro boards in these, but the PT-65B seems like a good option, especially price wise.  Don't get me wrong, Reactive Micro's product is well done and and high quality and super easy to install.  This option is a bit more work, but I can pretty nearly do all three of these supplies I have for the price of one...

 

 

 

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Oh, if anyone is interested

Oh, if anyone is interested in pics of these other power supplies and what I do to adapt Uncle Bernie's pattern to their slightly different layouts, let me know.

 

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Always share your solutions

I think it's always worth sahring your solutions to these kind of things. We can all learn from each other.

(My "best" trick, for instance, was using some acrylic as a layer between the Meanwell and the case. Insulative and allows you to mount the meanwell without having to drill holes)

 

Chesh

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In post #2, CheshireNoir

In post #2, CheshireNoir wrote:

 

"I'd like to see your take on this so put me as a +1 to showing uis the PT-65B conversion. "

 

In post #15, CheshireNoir wrote:

 

"My "best" trick, for instance, was using some acrylic as a layer between the Meanwell and the case. Insulative and allows you to mount the meanwell without having to drill holes.

 

Uncle Bernie replies:

 

Had I known about your website with your conversion, it would have saved me some time, and probably I would have avoided the pitfall with the hole in the bottom of the box. I think the internet has solutions for most problems, but the trick is to  find  them. And when you don't know they exist, you don't know how too look / search for them. So things get reinvented / work gets duplicated all the time. Still, much a better situation than back in the day, before internet. Public libraries were all you had.

 

I've looked at your website, and your conversion is nicely done. One comment, though, and this is about the little PCB with the capacitor on the 7905. IMHO, these added components are superflous. I am well aware that the datasheets of those regulators recommend adding bypass capacitors both on the input and output of these regulators, but as long as the wire to the PT-65B is not too long (which it won't be in this case), the output filter capacitor on the PT-65B will serve well as the input bypass capacitor of the 7905.  The output bypass capacitor is said to 'improve load step response' but as long as there is a small bypass capacitor on the Apple IIe motherboard, and the power cable has the same length as it has, no such capacitor is needed on the 7905. I think these recommendations in the datasheet were motivated by issues they have seen in the field where power supplies with the regulators were farther away from the load, and once the wires get long enough to add some inductance then load step response may indeed suffer. The input bypass capacitor may only be needed if the distance from the rectifier / filter capacitor to the regulator is longer than 1 ft. At least this is the length when we started to see first signs of instability / ringing when evaluating such regulators. Note that so-called "LDO" regulators react much less benign to such long wires. It's easy to destabilize LDOs or to turn them into oscillators. So better avoid LDOs unless headroom too low. The 78xx and 79xx regulator families are much more robust against such adverse conditions (long wires and poor or nonexisting bypass capacitors).

 

But it's up to the builders if they want to include these extra bypass capacitors or not. What I would NOT do in any case is to use a solid tantalum (despite, again, the ancient datasheets spell that out). Solid tantalums, especially when aged, are a fire hazard. So better, avoid them.

 

Your solution with the acrylic as an interposer to mount the PT-65B on the original standoffs avoids a lot of trouble with sheet metal work and is easier to do. But it's an insulator so the ground islands around the PT-65B screw holes make no contact with the sheet metal box. Now, you are down to one ground connection, and this the the one to the ground tab on the PT-65B. If this connection falls off / becomes disconnected, the whole power supply is electrically unsafe and also may radiate excess EMI. To save your concept, you could use sheet metal instead of the acrylic, or add at least one additional ground connection at one of the screws contacting the PT-65B PCBs. They make round contact thingies for screws, same sort you can see at the grounding bolt in my photos of the line voltage side, with a solder tab for a wire. You could use two of those and two star washers to connect at least one of the ground islands of the PT-65B to a screw / bolt which contacts the metal box. This will keep the PT-65B grounded even if the ground tab gets disconnected. The importance of grounding the switchmode power supply properly cannot be underestimated. These grounding islands are there for a reason.

 

- Uncle Bernie

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Excellent feedback

Thanks for the feedback!

I will definitely skip the caps in future, with your feedback. (I'm not much good at electronics. I tend to bodge a lot of stuff together, following schematics but not much further)

I will definitely revise the earth leads.

 

Cheers!

 

Chesh

 

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A middle route between the

A middle route between the acrylic and sheet metal methods is maybe similar to the one that Reactive Micro uses, which is a PCB.  It isn't as thick and insulative as acrylic and can have plated trhough conductive mounting points to facilitate grounding.  It probably wouldn't be hard to make a PCB that screwed down to the base of the normal power supply chassis mount points and provides mounting spots for the Mean Well PT65-B chassis to bolt to.  That PCB could probably be fabbed from somewhere like JLCPCB for $2-$5 each depending on shipping costs.  It could also have the screw down location for the LM-7905 on it and maybe even any other connectors needed to facilitate the hookup.  Just a thought.

 

 

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Another very cheap

Another very cheap alternative to ceramic or mica are the silicone pads: https://www.aliexpress.com/item/1005004613431383.html

 

If we go with the nominal current of 250mA written on the original Apple II PSU for the -5V rail, we end up with (12V - 5V) x 0.25A = 1.75W that needs to be dissipated by the 7905 regulator, which I think requires a proper heat transfer pad.

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I just got a notification

I just got a notification that the PT-65B that I ordered is out for delivery.  I have an AE power supply here which has the typical clicky-clicky type failure.

 

This particular one is a great candidate for this kind of board swap because I am not sure if the schematics, etc. for this are even readily available.  I bought it off eBay a while back super cheap because according to the description it is "re-capped but still not working".  IIt's probably a diode or one of the transistors, but it could even be as simple as a resistor but in this case just replacing the board is much easier than trying to diagnose what the actual failed component is.  And chances are a brand new board will give many years of trouble dree service.

 

I will be developing a variant to the methods discussed in this thread that fits that particular power supply case and I will post pics and details here.

 

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Well, so much for that. 

Well, so much for that.  Looks like Amazon has managed to lose another package.  "Was expected by Monday".  We'll see if it shows up tomorrow.

 

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OK, well it showed up late. 

OK, well it showed up late.  Better late than never.

 

 

 

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Here is what the AE supply

Here is what the AE supply looks like inside...  Quite a different mounting system to the way Apple does it.

 

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So my strategy here is just

So my strategy here is just going to be to cut a piece of plastic to the size of the original AE power supply board and mount it into place with screws like the original board was.  The PT-65B board will just be screwed down to that.  Then it is pretty much just making the hookups to the power connector/switch and the output side with the added LM7905 like Bernie's example.

 

 

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Does anyone have the part #s

Does anyone have the part #s handy for the connectors that fit on the power input and outputs for the Mean-Well?  I will probably order from either Mouser or DigiKey.

 

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Hi softwarejanitor!

According to a very detailed PDF (for 36 pages!) from the esteemed Uncle Bernie, you have to buy from Mouser:

 

IDC header female 6 pins,

for pin spacing 3.96 mm red 571-3-640428-6, white 571-3-640602-6.

 

IDC header female 3 pins,

for 3.96 mm contact spacing red 571-3-640428-3, orange 571-3-640426-3.

 

I hope I translated it right....

 

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Some comments on the connectors and the grounding !

In post #24, softwarejanitor wrote:

 

So my strategy here is just going to be to cut a piece of plastic to the size of the original AE power supply board and mount it into place with screws like the original board was.  The PT-65B board will just be screwed down to that.  Then it is pretty much just making the hookups to the power connector/switch and the output side with the added LM7905 like Bernie's example.

 

Uncle Bernie comments / warns:

 

When using an insulator plastic sheet as an interposer between the PT-65B and the metal shell (which requires less metalworking), do not forget to use at least one grounding lug at one of the two "safety gound / earth" PCB foil islands of the PT-65B, and connect that to the metal enclosure, which, if eloxated or painted, may need some grinding to the bare metal to make a good contact. Verify that this ground connection is low ohmic from the ground tab of the PT-65B to the metal enclosure. The reason for this was given in post #16. You want the PT-65 safely grounded even if the wire to its ground tab would fall off.

 

The IDC connectors mentioned by macintosh_nik can be used, but avoid the white ones, the slots in their contact springs are too narrow for the wires found in such power supplies. Strip isolation, twist and pre-tin the wires and then solder them into these IDC connectors (from the top). You do not need to drive the wires deeper into the contact springs because once the enclosure is closed again, none of these wires within will be wiggled anymore. Both the +5V and 0V/COM rails need two wires / contact springs, for both pins the PT-65B offers for each of them. The reason is that one of the IDC contact springs alone can't support the full rated output current of the PT-65B.

 

These IDC connectors  are a good replacement for the MOLEX connector system I've used for my mod - - - these need a heinously expensive crimp tool and the crimp contacts which have to be bought on a reel of 1000 pcs.

 

While you making your order to Mouser, you may also add this connector for the PT-65B grounding tab (it's a crimp type, but solder the wire into it unless you have the expensive special crimp tool, and not the cheap Chinese made toy pretending to be the tool):

 

Faston connector for 5.21 x 0.72 mm tab.

TE Connectivity part #640911-1.

Mouser part #571-6409111

 

and if needed, the line cable connector, too. Oh, and Mouser would also have sold you a PT-65B (or PT-45B) as an official distributor of "Mean Well" products. No need to buy from dubious sellers on Amazon or Alibaba. One of my beta testers for the +8V mod got defrauded by a Chinese scammer who sold him a badly replaired, old PT-45B they obviously had fished out of the electronic junk recycling stream, and for the same price Mouser rings up. All he "saved" was the postage. And the time spent for  hunting down the fault would have cost  thousands  of US$ if it wasn't a hobby.

 

- Uncle Bernie

 

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Macintosh_nik wrote:According
Macintosh_nik wrote:

According to a very detailed PDF (for 36 pages!) from the esteemed Uncle Bernie, you have to buy from Mouser:

 

IDC header female 6 pins,

for pin spacing 3.96 mm red 571-3-640428-6, white 571-3-640602-6.

 

IDC header female 3 pins,

for 3.96 mm contact spacing red 571-3-640428-3, orange 571-3-640426-3.

 

I hope I translated it right.

 

Do those include the metal parts or do those need to be ordered separately like some connectors?  I'm getting ready to order some parts from Mouser and given the high shipping costs these days I want to make sure I get everyting in one order.

 

 

 

 

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I didn't know that Mouser

I didn't know that Mouser sold the Mean-Well power supplies.  Maybe I missed that if it was on one of the threads.  They're about the same price as other sellers too.  If I'm already ordering from Mouser then the shipping isn't such a big deal.

 

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I checked the Platinum //e

I checked the Platinum //e Dynacomp power supply I mentioned earlier...  Turns out I already put one of Reactive's power supply boards in that one so it is good to go.  I am going to ordere another Mean-Well PT-65B from Mouser when I order the rest of the parts.  That one will go in the Franklin power supply case that I have.  It will require a slightly different mounting set up than either this AE supply or the Apple supplied ones.  I will document that one as well so futre people will be able to take advantage of that.

 

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More Tips & Tricks about IDC connectors:

In post #28, softwarejanitor asked:

 

"Do those include the metal parts or do those need to be ordered separately like some connectors ?" 

 

Uncle Bernie answers:

 

Yes. These IDC connectors come with the contact springs installed. But you can take individual contact springs out: depress the latching tab with a pointed tool, and then pull the spring out from the top using tweezers (or needle nose pliers). If you do that on positions #2 and #4 of a 6-pin connector, and then cut the plastic shell at the now empty position #4, you have turned a 6-pin IDC into a 3-pin IDC with the middle contact missing (for air gap) and this is the right one for the line voltage input of the PT-65B. This is why I recommend to buy 10 pcs of the 6-pin connectors, once you have Apple-1 around, or want to put PT-65B into an Apple II, you have all you need in stock. These are very cheap and very useful connectors.

 

- Uncle Bernie

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UncleBernie wrote:In post #28
UncleBernie wrote:

In post #28, softwarejanitor asked:

 

"Do those include the metal parts or do those need to be ordered separately like some connectors ?" 

 

Uncle Bernie answers:

 

Yes. These IDC connectors come with the contact springs installed. But you can take individual contact springs out: depress the latching tab with a pointed tool, and

 

 

I ordered the connectors and another PT-65B to go in the Franklin power supply chassis I have.  I went ahead and ordered some exrta connectors so I will have them on hand.  Everything I need should be delivered within the next week.

 

I will post pics and details on the Franklin PS conversion as well.  Between these and the Apple ones we should have some pretty solid documentation laid down for people to reference in the future.

 

 

 

 

 

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Some power supplies come on

Some power supplies come on the instant you flip the switch while others come on a second or two after. Which one is the PT-65B?

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UncleBernie escribió: En la publicación #6,
UncleBernie wrote:

In post #6, softwarejanitor wrote:

 

"How are you getting the -5V output?  Adding another regulator like an LM7905?  If so, which other output do you tap to get the power for it the +12V?"

 

Uncle Bernie answers:

 

The PT-65B makes -12V and so it's cheap to add a 7905 regulator to provide the regulated -5V rail for the Apple

 

I like the idea. Thank you . I take good note.

But...excuse me...you directly connect the LM7905? Since I don't know how it works, I found this...

 

 

 

You connect it directly from -12v ??

 

 

 

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On Uncle Bernie's example he

On Uncle Bernie's example he leaves out the capacitors because the PT-65B already has sufficient filtering.  That simplifies things greatly.  Basically just split the -12V off into the input of the LM7905 and of course hook the ground to ground, and the output goes directly to the -5V output.  All that is needed is a proper heat sink.

 

 

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Thank you, because I have to

Thank you, because I have to translate the page to understand it... I had not understood it.

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On power up / power down sequencing and the like.

In post #33, Wayne asked:

 

"Some power supplies come on the instant you flip the switch while others come on a second or two after. Which one is the PT-65B ? "

 

Uncle Bernie answers:

 

Under typical load conditions, a PT-65B (or PT-45B) takes somewhere from 1-2 seconds to bring all the output voltages up.

 

For most applications, this is a non-issue, and the original Apple II power supply also took some time to "start up".

 

In both the PT-65B and the PT-45B, the +12V rail is developed by having one output winding of the pulse transformer "riding" on the +5V rail (with a rectifier diode, of course). So at least during power up, the +12V rail never should have a voltage lower than the +5V rail. When the power is turned off, however, the situation depends on the loads seen by both rails. But according to my measurements, it's never more than one diode drop difference. But the +12V (V2) rail indeed may have one diode drop lower voltage than the +5V (V1) rail during power down.

 

Back in the day, most ICs were robust enough not to get damaged with sluggish or random power up or power down sequences. Very trivial solutions - such as diodes between +5V and +12V rails) could be adopted to prevent that the +12V rail ever was lower than the +5V rail by more than one diode forward voltage drop. Same trick can be applied to negative power supply rails. If Schottky diodes are used, with a forward voltage less than a PN junction, then nothing bad can ever happen to the ICs (normally).

 

But with "modern" ICs with various "core" and "IO" voltages (or some special functions, like LCD drivers etc.) a strict power up / power down sequence may be mandatory, otherwise these ICs would get damaged. For this purpose, the semiconductor industry offers various families of "power sequencer" or "power system management"  ICs. Before retirement, I worked as an IC designer for one of the leading semiconductor companies, and believe me this topic can get very complex and mind boggling. Imagine what happens when somebody jerks the line cord of such a system out of the outlet. How can you detect that event in due time such that the (safe) shutdown sequence still can be completed ?

Or worse, what if one of the many dozen lower level switchmode power supplies / supply voltage converters on a $10000 PCB blows up and that output voltage is lost (almost) instantly ? There are IC which can draw 100 Amps at 0.8V core voltage. What to do to avoid damage to the sensitive multi supply voltage ICs on that board ? --- This is why the effort and expense to design and develop a proper power supply concept for such system can become very high, often higher than planned.

 

For me (now being a mere hobbyist) yet another reason to avoid modern FPGAs having multiple "core" and "IO" voltages like the plague.

 

- Uncle Bernie

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Got to love Mouser... 

Got to love Mouser...  overnight delivery, regular frieght UPS charge.  They must sell a lot of parts to one of the tech companies near me or something, because shipping from them to here is always AMAZINGLY fast.

 

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Now that I'm looking at

Now that I'm looking at putting everything together I had a weird thought.  I'm almost tempted to drill and tap a screw hole into the end of that big heat sink on the PT-65B and screw the LM7905 down to that.  Maybe even just drill the hole and use a self tapping metal screw.

 

Am I crazy?

 

 

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Don't connect any 79xx TO-220 tab to GND !

In post #39, softwarejanitor  wrote:

 

" Now that I'm looking at putting everything together I had a weird thought.  I'm almost tempted to drill and tap a screw hole into the end of that big heat sink on the PT-65B and screw the LM7905 down to that.  Maybe even just drill the hole and use a self tapping metal screw.

Am I crazy ? "

 

Uncle Bernie answers:

 

No, doing that is not crazy, but it is dumb, because you would create a short circuit between the V3 output rail  (-12V) and COM/0V.

 

In other words, it won't work. Most likely, the 7912 regulator on the PT-65B would protect itself from overload and limit the current, so nothing will blow up immediately, but nowadays, who knows who made the 7912 and on which process technology. Back in the day, when USA based wafer fabs owned by reputable semiconductor companies made them, based on the original American design of the late 1960s / early 1970s, these regulators were almost indestructible (I know tricks how to destroy them, though, like the infamous "file test" using long lab cables for inductance).

But nowadays, fly by night no-name Chinese wafer fabs making them at 5 cents a piece, possibly based on stolen / reverse engineered mask layouts, who knows. I encountered one Chinese made 7912 which had such thin leadframe that it delaminated and cracked the die (aka "chip").

 

The metal tab on 79xx TO-220 regulators is not connected to 0V/GND (like on the 78xx) but it is connected to the input voltage, which is the most negative voltage a 79xx  sees on any of its three "pins". The deeper reason is that it's a junction isolated bipolar process, and the p-ISO structures isolating the NPN collector tubs (N doped), actually are PN junction diodes, which always must be reverse biased, otherwise, everything in the IC gets connected via these diodes opening up, which is bad ! These p-ISO structures are ohmically connected to the the p-substrate (the "die" = chip) and this is bonded to the TO-220 carrier, aka leadframe, with an ohmic contact. So there is absolutely no other way to build these negative regulators cheaply. You could use film attach to isolate the die from the lead frame  but that costs more money, and these IC are penny items. There exist versions of these regulators with a fully plastic encapsulated body and mounting tab. But these are much more expensive and harder to find.

 

A solution you could try is to take out the screw of the the 7912 regulator on the PT-65B itself, and then use it to attach the 7905 regulator right there, such that the tabs mate. Installation on the opposite side of the heat sink is not possible (at least on my specimen) because they have a bulge there in the metal which contains the thread for the screw. Since you now have connected the 7905 to the raw negative input voltage via the tabs, all you need is to add a small ground return wire and the fat wire for the -5V would directly go to the output of the 7905. Be aware that the ground return wire is essential. If it ever breaks off, the output of the regulator will go to the input voltage, and now you've got unregulated -20V (or more) instead of -5V regulated.

 

Still, why make such an ugly kludge. You can buy isolated mounting kits for TO-220 like the one I did use.

 

- Uncle Bernie

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OK, fair enough.  This is the

OK, fair enough.  This is the reason why I ask here first!  I don't purport to know everything, but there are plenty of people here who know a lot more than I do.

 

Thanks for the clarification on the 79xx vs 78xx as far as the heat sink being grounded!  Looking more carefully at the 7912 on the PT-65B, I now see that it is the part with the small steel heat sink attached to it, and that heat sink does not attach to anything else.

 

I wll install a separate heat sink for the 7905.  I think I have a bunch of them left over from another project.

 

I'm learning...

 

 

 

 

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On "unconnected" heat sinks . . .

In post #41, softwarejanitor wrote:

 

"And that heat sink does not attach to anything else".

 

Uncle Bernie cautions:

 

That heat sink is still connected to the TO-220 tab which is connected to the input pin of the 7912.

 

(Beware of "invisible" electrical connections --- this also applies to the heat sink of the primary side swicthing MOSFET, which is "hot" = electrical shock hazard).

 

-  Uncle Bernie

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softwarejanitor wrote:Now
softwarejanitor wrote:

Now that I'm looking at putting everything together I had a weird thought.  I'm almost tempted to drill and tap a screw hole into the end of that big heat sink on the PT-65B and screw the LM7905 down to that.  Maybe even just drill the hole and use a self tapping metal screw.

 

Am I crazy?

 

Doing that is perfectly fine, as long as the metal you are attaching it to is not on the high voltage side and you use a ceramic, mica or silicone isolating heatsink pad + isolating washer like the one I mentioned in responce #19 above. Without that you end up with a short.

 

Also always double-check that there is no electrical connection after you fasten it.

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Here is it protyped with a

Here is it protyped with a piece of cardboard instead of the plexi.

 

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Here is the plastic cut to

Here is the plastic cut to the size of the original AE power supply board ready to be drilled.

 

Here is the power supply mostly assembled, just needs to be tested and have the cover put on.

 

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Well, I finally got around to

Well, I finally got around to testing this with one of my Taiwan ][+ clones and it works fine.  I will probably get to the Franklin power supply next.  It is a completely different layout plus it has an AC powered built in fan, so it will require some differnt wiring.

 

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