Apple //e color composite monitor help needed...

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Apple //e color composite monitor help needed...

Anyone have advice on troubleshooting a apple model a2m6021? Got no power, I haven't found schematic so obviously prior knowlege will be important. But before the easy electrical stuff I have a physical issue that I can't figure out... it appears the back panel isn't separating from the case when opening it up, is that correct? Shouldn't that powre/control panel stay with the frame  not the case?

EDIT, I decieded to see if it was just friction and carful pressure I was able to get the case free of the panel and it's open now. Basic check and all fuses I could find are good. I don't see any obvious damage, everthing looks brand new there's not even much dust inside. I'll start probing the board but if anyone has a squence for this system tthat would be helpful. 

Thanks. 

 

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The 8-Bit Guy has a 2-parter

The 8-Bit Guy has a 2-parter on this monitor that should help with the mechanics, but looks like you already figured it out: https://youtu.be/xzba3iV2nxA

 

It doesn't look like the schematics have been released to the public, but there is a lot of material out there from guys helping out each other: 

https://www.aussiearcade.com/topic/87446-apple-a2m6021x-monitor-repair/

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Thanks, and yea the 8-bit guy

Thanks, and yea the 8-bit guy was the reason I understood the back panel should not be lifting with the case. =)

I've been probing around so the schematic would be super helpful. When power is applied I don't hear any of the typical CRT power up, and that's not great but give me a path.

I've checked the switch itself and found 120VAC at F901 so that's working. The LED isn't lit, I'm guessing it's just a bad LED. I didn't disassemble the switch to confirm but should.

I moved on to checking voltage at F902 and while labeled 125VAC 1A I'm not seeing much AC voltage there. I'm assuming this is AC but wihtout the schematic I'm not sure I'd also like to understand the use of this fuse so I'll probe around and see if I can find the path back to the switch.

 

Unfortunately I can't see many of the images in the writeup palindrome shared. But I'm in agreement to first verify the power supply section is working correctly...  just need to find the outputs.... maybe I'll search for another monitor using the same Samsung 37GGA67X CRT for a reference design Apple may have used. I dobut the FCCID will be helpful at this point in time, but decades ago may have produced the schematics. 

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More progress, but nothing

More progress, but nothing helpful. I confirmed the 3 power LEDs in series are good at 1.8V. I also found the voltage between J4 and J5 wires near the  C902 is around 155V DC which I think is right, just not totaly sure if that should be AC  or DC as I haven't located any rectifier diode bridge. I haven't probed C902 becuase the board is still installed.  I did check pins 9 (VCC )and 18 (gnd) of HA11423 and found only a few milivolts.  I'll check if I can find where the voltage gets stepped down to the lower DC voltages which may be more obvious if I pull the back panel there's a transformer that's a likely suspect but it also looks to be with a box which handles input and signal conditioning but it may be mounted outside that region....

I also measured the current through the degausing coil and that's just like 12mA. System power up insrush current is around 800mA then drops to 120mA so clearly not right for a CRT. 

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J4, J5, C902 - without a

J4, J5, C902? Without a picture no one knows what you are referring to.

 

Doesn't the power board on the side have all the voltages? Is it a switching PS or linear?

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CVT wrote:J4, J5, C902?
CVT wrote:

J4, J5, C902? Without a picture no one knows what you are referring to.

 

Doesn't the power board on the side have all the voltages? Is it a switching PS or linear?

Great point and question. I'm assuming it's switching although I'm not sure I'm going back and forth if linear would be better in a CRT and I didn't see the the components for that, but I also haven't done a good analysis of the board. That said there was a big regulator stuck on a heatsink that I didn't look at... that may have been important. Here's a picture (hoping it will scale down) C902 is the black cap 200V, 680uF. J4 and J5 are just the wires near the fuse. Someone suggested on that site you linked this may be a similar design to the Samsung 20K20 TV and the power in looks similar but I didn't get too far in analyzing that I was more just looking for similar parts wired the same and I only had visibility into the topside of the board so I didn't get too far. The Samsung TV has a STR3125 (STR30125?) which is a beefy regulator but 125V output, which would needs a secondary drop . 

 

I have no idea what the TDK component is near the finger. The blue wires near there (W1, W2) I believe are the degausing loop, so raw AC which does feed the anode of D903 at least that was the path I found.

 

 

 

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The TDK element TH901 is

The TDK element TH901 is probably the posistor in series with the degaussing coil that causes the fading of the sinusoid.

 

You should look at the back of the board, where everything is nicely labeled and it's easy to see where things go: https://forums.atariage.com/topic/337434-applecolor-composite-monitor-a2m6021/

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TH

"TH901" is a reference designator for a THermistor. I agree with the assessment of a PTC to limit current to the degaussing loop.

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robespierre wrote:"TH901" is
robespierre wrote:

"TH901" is a reference designator for a THermistor. I agree with the assessment of a PTC to limit current to the degaussing loop.

 

LOL, yeah not sure how I missed the TH label, doh!

 

Would you have any idea where 5V is derived from? 

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lopt?

5v (Vcc) might be produced by a low-voltage (about 7 VAC) secondary on the LOPT, followed by a rectifier and linear regulator.

These CRT monitor designs tried to save weight and cost by minimizing the number of transformers and that was one way it was done.

The other approach was to have a power supply module with a multiple voltage switching power supply. That would be easier to recognize (it would feed power to other boards with a multi-way cable). The power supply commonly was installed beneath a metal screen to reduce hum interference problems.

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You should check the voltages

You should check the voltages of the flyback. I know you don't have the schematics, but here are the schematics of my Taxan Vision EX, which is a japanese color monitor for the Apple II that is more or less from the same time period. They contain some voltages and oscillograms around the flyback. For example oscillogram 8 should be what you get on pin 10 of your flyback too. Be careful though, since these pulses are over 1kV.

(It's in high resolution, so open the image in a new tab)

 

 

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CVT wrote:Be careful though,
CVT wrote:

Be careful though, since these pulses are over 1kV.

 

 

Thanks, I don't have HV probes and think mine likey top out around 600V so will need to see if I can find some in a lab. My fear now is the flyback is bad since I don't hear the normal sounds from a working one.

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Finally got around to taking

Finally got around to taking another look and following CVT's suggestion I removed the bottom cover and started to probe voltages. But... I didn't really need to do that because I noticed a few cracks around the flyback mount which is not good. I found two broken traces  (if there's only traces on the bottom side, and I suspect it's a single layer board.) After adding some wire to patch the breaks I applied power and... power LED lit for the first time and CRT energized... that's promising.

 

But I didn't get a picture.  I found cracks across only across two traces so I didn't get deep in to verifying all wiring in that area. Random checks were good. My problem now is I have no experience repairing fiberglass boards, I can rework circuit traces, that should be easy but the fiberglass is an unknown. Obvioulsy repairing a trace witout repairing the base will likely just work until gravity causes another break. I suspect I can flex the board to expose gaps and inject a fiberglass epoxy but will that work? Any thoughts on repairing boards? Is it even worth trying to repair?

 

Here's a picture of the cracks:

 

 

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The only think I would do is

The only thing I would do is remove the color mask where the traces are cracked and tin them with solder. The boards of this era are also covered with this sticky gunk, but you can easily remove it with isopropanol or 95% ethanol from the pharmacy. Then use 600 grit sandpaper to remove the color mask and expose the copper trace, so it can be tinned. Be generous with the solder, because the flyback is heavy and if you drop the monitor it will try to bend the board. This is probably how it got cracked in the first place. And just to be safe, have copper wires make the connections anyway where the traces were interrupted before.

 

After you tin the traces, you can put some super glue on the cracks where there are no traces, but I doubt that it will penetrate between the cracks.

 

Also while testing, keep in mind that some color monitors from this era need a signal to produce a raster and without it the CRT doesn't light up even at maximum brightness.

 

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EHT good

If you're getting static charge on the screen, you know the EHT is functioning (the highest voltage on the flyback, which goes to the second anode cap on the CRT). You also know that horizontal deflection is working because on most sets like this, the horizontal sweep is the input to the flyback. Do you see a red glow from the cathode heater in the tube neck? The heater is the lowest voltage from the flyback (around 6 VAC).

Glass fiber circuit boards can be repaired if cracked, but it certainly is in "advanced" territory. The glass fiber is already there, you would use a thin acrylic-modified epoxy to wick between and around the cracks and then cure in a 60°C oven for about 30 minutes. Scrape away any excess buildup of epoxy and then patch or jump over where the traces were broken with copper and solder.

Search for information about "IPC 7711 section 3.5.1" which is the industry standard procedure.

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Addendum to CVT post

Addendum to CVT post regarding bridging the trace with solder ... (I think he indicates such, but for clarity)

Add a wire across each trace when bridging the joint because through heat, expansion and contraction, it will eventually crack the solder bridge at the break point.

Just a tidbit for longevity.

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macnoyd wrote:Addendum to CVT
macnoyd wrote:

Addendum to CVT post regarding bridging the trace with solder ... (I think he indicates such, but for clarity)

Add a wire across each trace when bridging the joint because through heat, expansion and contraction, it will eventually crack the solder bridge at the break point.

Just a tidbit for longevity.

 

Thanks guys I've got experience with repairing the traces, I am still considering wire bridging also considering expoxy copper foil then solder over and apply epoxy mask but both would prefer to have the cracks repaired/reinforced.   

@robespierre I'll take a look at that, I hope that means you are suggesting it can be fixered. I have a few lab tech friends that I may tap for help.  

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CVT wrote:The only thing I
CVT wrote:

The only thing I would do is remove the color mask where the traces are cracked and tin them with solder. The boards of this era are also covered with this sticky gunk, but you can easily remove it with isopropanol or 95% ethanol from the pharmacy. Then use 600 grit sandpaper to remove the color mask and expose the copper trace, so it can be tinned. Be generous with the solder, because the flyback is heavy and if you drop the monitor it will try to bend the board. This is probably how it got cracked in the first place. And just to be safe, have copper wires make the connections anyway where the traces were interrupted before.

 

After you tin the traces, you can put some super glue on the cracks where there are no traces, but I doubt that it will penetrate between the cracks.

 

Also while testing, keep in mind that some color monitors from this era need a signal to produce a raster and without it the CRT doesn't light up even at maximum brightness.

 

This was surprisingly a 93 monitor, and I didn't even think they were made that late because the II like was killed off in 92 proves as long as there's a market product will be manufactured!I was considering superglue, but like you said, getting into the cracks will be tough I have syringes and stuff I can use and CA glues are farily thin and flow easily. I just need to avoid further damage trying to open gaps. I don't totally understand your testing comment, I did have a IIe connected when I captured this: 

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OK

OK, so if you see a raster (a dark gray background covering the screen) that's a good sign. It shows that the important circuits of the display all are working. At this point, a lack of picture is pointing only to the video input circuitry.

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epoxy
jeff d wrote:
I was considering superglue, but like you said, getting into the cracks will be tough I have syringes and stuff I can use and CA glues are farily thin and flow easily. I just need to avoid further damage trying to open gaps.

CA glue is only rated to withstand 200°F or 90°C, which will be exceeded when you solder the jumpers over the cracks. (You want a rating of at least 350°F or 180°C for a circuit board: the board won't reach the soldering iron's temperature but it will get at least halfway to it.) They are also brittle.

A thin, wicking adhesive would be nice, but may not be necessary. If you desolder and remove the flyback transformer, and then grind the cracks with a Foredom so that they become little valleys, they will hold adhesives that are thicker. It's also permissible to build up the thickness where there are no component pads.

Chemtronics makes a two-part green epoxy that is recommended for repairing cracks in circuit boards: https://www.chemtronics.com/circuitworks-epoxy-overcoat-adhesive-syringe

Its viscosity is 11,000 cPs, like Lyle's Golden Syrup, and it withstands soldering temperatures. Epoxies as thin as 3,000 cPs are available from Henkel, Hernon, Saf-T-Lok, 3M.

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robespierre wrote:Glass fiber
robespierre wrote:
...

Glass fiber circuit boards...

...

 

This is not a fiberglass PCB. It's getinax.

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robespierre wrote:CA glue is
robespierre wrote:

CA glue is only rated to withstand 200°F or 90°C, which will be exceeded when you solder the jumpers over the cracks. (You want a rating of at least 350°F or 180°C for a circuit board: the board won't reach the soldering iron's temperature but it will get at least halfway to it.) They are also brittle.

A thin, wicking adhesive would be nice, but may not be necessary. If you desolder and remove the flyback transformer, and then grind the cracks with a Foredom so that they become little valleys, they will hold adhesives that are thicker. It's also permissible to build up the thickness where there are no component pads.

Chemtronics makes a two-part green epoxy that is recommended for repairing cracks in circuit boards: https://www.chemtronics.com/circuitworks-epoxy-overcoat-adhesive-syringe

Its viscosity is 11,000 cPs, like Lyle's Golden Syrup, and it withstands soldering temperatures. Epoxies as thin as 3,000 cPs are available from Henkel, Hernon, Saf-T-Lok, 3M.

 

 

The Chemtronics green epoxy was what I planned to use for both the copper foil to board and overcoat. But I didn't think it would be good for the board to board, I guess my thinking doesn't make sense.... I'll check the dataseets to see what they say about board bonding. I didn't think it's thin, seems to be fairly viscous. I can take a look at the others.I like the idea of cutting valleys to provide bonding surface area, it was something I had considered. Thanks for confirming that's a practical option.

 

@CVT thanks for identifying the substrate, that helps!

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