A few Apple II Rev0 questions

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A few Apple II Rev0 questions

Hello fellow members,

New member here,  Would like to say hello and glad to be part of the community, not new to Apple IIs though. Ive just completed assembling a Rev zero replica board and upon initial boot, I got no boot, no video, but ticking from the PSU. No power light on but did flash when I powered it off. The PSU has been recapped and tested good readings. The power bulb has been tested as well. All LS logic ICs were tested on a mini pro before installation and the Integer Basic ROMs were supposedly tested from a trusting source. There are no "dots" on the board designating #1 pin on the resistor arrays so I installed them like my ii plus boards RA1 with #1 pin farthest away from the keyboard and RA2 and RA3 installed with #1 pin closest to the keyboard. Are these installed the same on the ii plus as the rev0? All resistors, transistors and the 6502 were tested as well before installation.  I'm currently in the process of checking all the sockets making sure no solder jumped to another leg of the sockets. All card sockets, all pins have no continuity between them, all clean. I get continuity from the 5V pin where the power comes in to all ICs that have 5V, same for 12V at the 8 RAM. The ground post has continuity to everything that has a ground leg. I've been trying to find out , and I cant seem to get an answer, is do all 3 memory select jumpers need to be installed? I am currently only populating zero bank with 4116s and I have only 1 jumper installed at the D1 location.  I have the "Red Book" and have read the section about installing more ram, but it never mentions anything other than how to wire the jumpers to corrospond with whatever RAM you use. I guess what I'm looking for "if you have THIS bank popuated, THIS is where the jumper goes for that particular bank." What did this board look like when someone bought it in 1977 with just enough RAM to get it booting for the customer. Thank you all for reading this and hopefully someone can shine some light and point me in a direction. 

Thanks all,

Randy

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If your PSU is ticking, you

If your PSU is ticking, you mosy probably have a short. Great that you checked continuity from the +5 and +12 rails to all of he chips. Now you need to check for short between one of those rails (most likely +5) and Ground!

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Have you tried turning it on

Have you tried turning it on and off again?

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Hi mochatea396!

As I recently found out there are 2 types of replica Apple II rev.0, the author of one respected Mike Willegal and the other has an error. I will attach a couple of photos, the second with the error.

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That's good to know. I'll

That's good to know. I'll have to check my board for which version I have. I did get mine a few years ago so hoping its the Mike Willegal version. I got it about the same time I picked up a coulpe of Apple 1 Newton boards.

I've just done the Improved Video Sync Generation mod for my Rev 0 board as discribed on Mike website.

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Thanks nik,Thats interesting.

Thanks nik,

Thats interesting. That looks like something on the ground circuit. I'll look at that when I have the board back out again. Ive done more testing. I've unplugged all socketed chips and powered on an the ticking is gone. Light stays on nicely on the keyboard.  I started populating the board and got it fully populated, powered on and no ticking. Plugged the keyboard in, and the shorting is back. Unplugged the keyboard again, and the ticking is still there. I tested the keyboard on a working ii plus and the keyboard is fine.  I started removing one row at a time and powering each time and it kept ticking, until I removed the row with the ROMs. Then the ticking stopped. I powered it up fully populated with everthing EXCEPT the ROMs WITH the keyboard connected and no ticking. Power light stays on nicely on the keyboard. So the issue is in the ROM sockets. I tested the ROMs on a ii plus and they boot the ii plus. (Do integer basic ROMs work in a ii plus? It beeps and boots but I cant get an asterik like the book says I should see , just a flashing cursor) I get 5V to the 24pin and ground to the 12pin on all ROM sockets and nothing from the 5V is bleeding over to any other socket pins. Big time head scratching. 

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Still sounds like a short on

Still sounds like a short on the motherboard. Probably comes and goes as you flex the board while removing/inserting chips. Might want to also check the back side (or remove from the case) to eliminate any shorts to the bottom plate.

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I checked my board in the

I checked my board in the area mentioned about a defect. Looks ok to me. But thanks for mentioning that. 

I do however see something I don’t like. Intermittently I’m getting continuity between my +5 and ground. I checked it last night and I had no continuity. Checked it this morning before I removed the board and there was continuity, removed the board, and no continuity. So it sounds like Jeff May be on top of it. Maybe put the ROMs back in and not snap the board into the frame, make sure there’s no overlap between the rails one more time and try to boot.  If THAT is the issue, where is shorting? That’s a tough one 

Thanks everyone for the inputs

 

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can you post photos of your

can you post photos of your board at those locations?

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Here's the area of the board

Here's the area of the board in question.

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 mochatea396 wrote:... where

 

mochatea396 wrote:
... where is shorting?

 You definitely have an intermittent short. With the motherboard out of the case you can check for the short on the +5 rail. Then gently flex the board in all directions from different points until you isolate the area where it is coming from. Could be a shorting solder joint, trace, or even something underneath a socket. Possibly one of the bypass caps in that area shorting (just tap or manipulate each one to test). Good luck. With patience you'll find it!

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Thanks Jeff, One other thing

Thanks Jeff, One other thing I was confused about. I don't know if I mentioned intermittent continuity between rom pins 24 and 12. Those are the +5V and the ground.  This continuity is inermittent. I tested those pins on 2 fully working apple ii plus machines and EVERY rom has continuity between pins 24 and 12.  The +5 and the ground! How can that be? I get continuity from the +5V pin 24 to the PSU case. This is on 2 working machines! Intermittent on the Rev0. Obviously if Im getting continuity on working machines, how this is, is beyond me, then it must be right. And the lack of it on the Rev0 board could be my problem.  This one is really stumping me. If someone could confirm these 2 ROM pins are supposed to have continuity, that would answer a few questions. I'm far from an electronics expert but I would interpret ANY voltage rail contacting a ground rail would equal a short, but perhaps I need to be schooled.

Thanks

 

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If you're using your meter in "test continuity" mode...

Hey there,

I've been fooled in the past by seeing things as "shorts" where there were really capacitors inline, or, in extreme cases, a resistance, just a very low one.  Try measuring the ohmage rather than just using continuity mode?

 

Cheers!

 

Chesh

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Like Chesh said, measuring

Like Chesh said, measuring across the +5 rail to ground will yield a small resistance (about 5 ohms). A true short would drop that to less than 1 ohm depending upon where you measure it. You need a decent ohmmeter and make sure it reads 0 when the leads are shorted.

 

Now, if your Rev 0 board intermittenly shows a high resistance when you flex it, then you may have a broken (open) trace which is just as bad. Although it should be easier to locate. But that would not cause your PSU to chirp.

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Today I tested the 12 and 24

Today I tested the 12 and 24 rom pins on the ii plus board to check for resistance. I was getting 8.3 on all ROMs. I had a feeling my meter was beeping as continuity because the resistance was so low. I tested a spare 10ohm resistor and low and behold it beeped with continuity. So that explains that. On the Rev0 board however I was getting resistance readings like 181! I flexed the board a bit and tested them later on and the readings were significstly higher. I thought maybe the meter, I checked the ii plus pins again and they were exactly what they were before. So I doubt it’s the meter. I’m going to check the Rev0 again with another meter hopefully by this weekend and see if the readings are the same. But nevertheless I would think I should be getting readings close to the ii plus in the 8.3 range. Both those pins have the trace inside the board I believe also. The middle layer. I don’t see anything on top or bottom. 

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You should try to connect the

You should try to connect the meter probes with alligator clips so you can wathc the reading while you flex the board. That should help you narrow down where the issue is. Also, I believe the board is only double-sided. There should not be any internal layers.

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Thanks Jeff, I got a set of

Thanks Jeff, I got a set of testing wires with clips today and I was able to free my hands up to flex the board while testing. I clipped the leads to pins 12 and 24 of ROM F8 and I was getting an OHM reading of 164.7 with the PSU connected. (Not powered obviously) when I flex the board a bit the readings don’t change. That number is way too high as I was getting readings of like 8.4 if I remember on the working g ii plus board. So if flexing doesn’t change the readings it doesn’t appear to be a bad trace. Where do you suppose I poke next?

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So has the power supply

So has the power supply completely stopped ticking?

 

Maybe there was a short that you have now permanently fixed. Or worse, turned into an open. You'll need to do some continuity checking to see what's happening.

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The PSU doesnt tick when the

The PSU doesnt tick when the roms are removed. And the keyboard light comes on steady. When the roms are installed, thats when it ticks and the keyboard light doesnt come on. I've been checking and checking for continuity everywhere and I can't come up with any culprits yet.

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 mochatea396 wrote:The PSU

 

mochatea396 wrote:

The PSU doesnt tick when the roms are removed. And the keyboard light comes on steady. When the roms are installed, thats when it ticks and the keyboard light doesnt come on. I've been checking and checking for continuity everywhere and I can't come up with any culprits yet.

Oh, was the 164 ohm reading with the ROMs removed? What does it read with all ROMs inserted? Maybe try with just the F8 ROM inserted.

 

If you're getting the ticking when the the power rails read 164 ohm, then I'd suspectthe power supply (even if it puts out the correct voltages with the ROMs removed).

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What ROMs are you using?  A

What ROMs are you using?  A rev 0 board...  really any ][ or ][+ mobo using Apple's original circuit designs can't handle 2716 type EPROMs without adapter sockets.

 

Are the ROMs you have original Apple ROMs?  Do they work in another mobo?

 

 

 

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Thanks for joining in the

Thanks for joining in the discussion,

These are original integer basic ROMs not 2716s.  And I have a 2513 character ROM.  I put the ROMs in a working ii plus with the 2513 keyboard rom and it booted. Strangely when I ctrl reset it, it beeped and blinking cursor at the bottom. I followed the steps in the red book to get a cursor that typed but I couldn’t. Cursor moves as I type but no characters are displayed. The steps didn’t seem too complex to do it wrong. 

The high ohm readings I am getting are with the PSU off. Not ticking because it’s off. ROMs in it ticks. ROMs out it doesn’t tick. Checking several ICs from the ground pin to the VCC on the ii plus they all show resistance of 6.7. Everyone I check on the Rev0 board shows 167 at the VCC to the ground. There’s something not right with the +5 circuit and the ground. Obviously they are connected with extremely low number on the resistance. I have to find out why I’m not getting it on the Rev0. 

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The forum attempts in helping

The forum attempts in helping you would greatly benefit from a photo. Make a photo of your populated motherboard from straight above and post this. Use a high resolution, so we can still read the markings on the ICs. That would explain a lot of things, without requiring to ask for every detail.

 

    mochatea396 wrote:

    Obviously they are connected with extremely low number on the resistance.

That was just floppy working, I guess. But just to state the obvious: the resistance between the +5V rail and GND is a simple result of many ICs being connected in parallel. Each logic IC has a resistance between its Vcc and GND pins of somewhere between a few Kilo-Ohms to several Mega-Ohms. I have a 6502 lying around, it shows 33K Ohm, a ROM about 3K, a simple 7400LS TTL logic IC about 38Mega-Ohm, a 74LS245 bus driver about 38K etc. It's the fact that they are all connected in parallel which results in the low resitance (simple maths: Rtotal = 1 / (1/R1 + 1/R2 + ... + 1/Rn). So the resistance depends on how many ICs you have plugged - and on their type. So, the resistance will also vary with the number and type of RAMs you plugged, for example.

 

But as others have already stated above: use a known to be good power-supply. If that's a power-supply which you have just recapped etc - and never reliably used under full load, then don't trust it. Use a tested supply that has proved to be working with another mainboard.

And one more detail: the resistance between the rail and GND which you can measure with a simple Ohm meter, does not reflect the true power demand of the mainboard, once the CPU comes to live. Once CPU reset is released, the CPU starts fetching instructions and distributing its clock signal all across the motherboard, the power demand dramatically increases. If the PSU is too weak to handle this, it will shut off and may also "tick". And, yes, the power demand will also depend whether the (boot) ROM is plugged, since without it, the CPU won't live very long.

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