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Author Topic: Does anyone have a spare Lisa motherboard?  (Read 2241 times)

rayarachelian

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Re: Does anyone have a spare Lisa motherboard?
« Reply #15 on: November 13, 2019, 11:00:44 am »

I think I'm making progress! I have patched every bad trace that I can find on the I/O board and now the power light will turn on and stay on when I hit the switch.

Woohoo! Congrats!

If I press the power switch again after turning the computer on, it will turn back off, but only if I let it run for about 20 seconds before trying to power off. There is still nothing on the display, though. I don't even hear the high-pitched whine that CRTs make when they are on, so I suspect that there is something wrong with the circuitry that drives it. Does the CRT turn on when you press the power switch or does it require a signal from a board in the card cage before it energizes? If it requires some sort of signal before it turns on, then I probably have a problem with the CPU or I/O board, but if it turns on with the rest of the computer, then I may have to mess with the video board to make it functional.

You might still have power supply issues, wetware RAM may be unreliable, but from what I remember the +/-33V lines are what power the CRT.
If you take the top off and turn the lights off you should see the back of the tube glow a bit where the cables go in. Don't do this just yet, read the rest of this.

I'm assuming you've already played with the brightness and vhold controls in the back of the Lisa?

So the contrast is controlled by a latch on the I/O board attached to one of the VIAs, but if the CPU board is dead or it has no RAM, it won't tell the VIA to set the contrast to a visible setting. So if there's a problem anywhere in that chain, you'll also get a black screen, but it could be lots of other issues from not being able to access RAM, or a dead CPU board or anything else like dirt on the contacts of the motherboard or broken traces between the CPU board, motherboard, or the connector or cable going to the analog board.
So next we'll want to try get some video output, any output, even if it's just turning up the brightness all the way and getting a white glow from the CRT. If you can't get the CRT to light up at all, or glow in the back, could point to the power supply.

If you're getting just one dot on the CRT and nothing more, it could mean that the flyback transformer is dead, or could be the VSROM or associated circuitry on the CPU board.

see: https://lisafaq.sunder.net/single.html#lisafaq-hw-vid_jumpy and especially read the whole video section and pay attention to the safety warnings. I'd suggest wearing insulating gloves when you do that and keeping one hand behind your back. CRTs are very dangerous and they can kill you. If you know all this already, and you seem to, then great, I don't mean to be telling you basic stuff, but I don't want some kid, a few years from now, who never saw a CRT in their life before, reading this forum and then sticking their hand in around a CRT and getting themselves killed.  ;)

Now, the next step would be to either purchase a flat plastic screw driver kit - I mean the blade is made of plastic or other non-conductive material, not just the handle of a screwdriver. You could also use a really small spudger with a flat end, or to cut a plastic knife into the blade of a flat screwdriver.

If you don't feel like cutting a plastic knife yourself, you could buy something like these which are ceramic bladed, but it's a waste of money. ( https://www.amazon.com/REAMTOP-Slotted-Ceramic-Alignment-Screwdriver/dp/B06XGF8Q8Q/ )

The reason you need this tool is that the next step will deal with you opening the top case and poking around the analog video board and should the screwdriver fall in, you don't want it to a) break the CRT or b) short something out, or worse c) electrocute you, so a plastic disposable knife is the best tool for this job, but you'll need to cut the blade into the right size to fit into the trimpots that you can use to adjust the video board controls using diagonal cutters.

Now, after you remove the front face of the Lisa, remove the card cage, and go underneath the top of the Lisa at the top, you'll find some screws. Undo those and you'll be able to remove top of the Lisa's case. You can see this (in reverse) here: https://youtu.be/ZXL2Ku23nSc?t=360 and a better one here: https://youtu.be/0r-zLeYygzc?t=1293 (at those time codes).

You'll need to insert something into the power cut off switch at the bottom left of the Lisa's face, like some rolled up PostIt note or whatever, and also into the hole at the back of the power supply where you see the back door has a bit of plastic sticking up. This will allow you to turn the Lisa on without these covers, which is dangerous and why those power cut off switches are there.

Reinsert the card cage after you've done this and now the Lisa should be topless, and backless  :-[ :o and yes, ofc, faceless.
Power it on. Wear gloves and with one hand behind your back, use a magic marker to mark the original position of all the trimpots - you'll move them very slowly and gently while the Lisa is on and one at a time. The trim pots may have some wax on them to keep them in the factory position, but you'll be breaking that seal if it's still there.

Next use the plastic screwdriver to gently and slowly move the trim a little bit at a time pots back and forth to try to adjust the video. If you've got any sign of video - even if it's just a white glowing screen, great, if not, you've got more debugging to do. If one trim pot doesn't produce results, bring it back to the original position that you used the marker to note it.

Since you don't have a working speaker you don't know if it's beeping, or if there's a RAM issue or whatever. It might be worth fixing the two transistors just to hear any warning beeps. Beeping would be a good sign that the CPU and the boot ROM are good even if the RAM might not be or something else is wrong. Perhaps you could trace the sound output pin off the VIA - should be the output of the shift register, maybe CB1 or CB2 or CA1 or CA2, sorry too lazy to look it up right now, and then attach a logic probe between that pin and ground to that and listen to the beeps, if any, that way.You can find what the warning beeps mean here: https://lisafaq.sunder.net/single.html#lisafaq-hw-rom_beeps
I could suggest trying to get an external monitor attached to the video out RCA jack, but likely that will be near impossible even if the video is fully working since that output is so weird - I've tried and haven't gotten very far with normal SD video stuff.

So what this tells you so far is that the COP421 is working and powering on and off (most of) the system. What you don't know right now is, 1. is RAM good? 2. is the CPU board fully good? 3. Is the CPU ROM good? 4. is the rest of the I/O board good (though that shouldn't affect video except for the contrast latch and DtoA.)

If either the CPU board is bad or the RAM isn't accessible, or the contrast latch on the I/O board is bad (or not set by the CPU) you'll also get a black screen and some beeping.

If you have a logic analyzer or even a logic probe you can poke around and see if there's some signals going in and out of the CPU. If you have a fox and hound cable tracing system (like this one: https://www.amazon.com/Meterk-Multifunction-Instrument-Maintenance-Continuity/dp/B071K8L32H/ )  you can use just the "hound" part which is really just an AM radio to pick up signals from the various boards and you should hear some noise as you move near each component. You won't be able to hear the really high frequency signals from the 68k, but you'll hear enough noise from other parts without even touching any pins to give you a rough idea to know if something is working.

It would really help if you had access to another Lisa so you can swap parts and see what's working or not, but if you're not near anyone with a Lisa, no worries, just keep poking at it.

You've made some really great progress, don't stop now, keep going, you're getting closer. These kinds of debugging things are like an onion where you're peeling off layer after layer of problems, but you don't really know how many layers deep there are to go.
« Last Edit: November 15, 2019, 07:56:53 am by rayarachelian »
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AlexTheCat123

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Re: Does anyone have a spare Lisa motherboard?
« Reply #16 on: November 13, 2019, 01:31:49 pm »

Thanks for the suggestions! I will try messing with the trimpots on the video board and probing the audio signal on CB2 of the VIA with an oscilloscope when I get home from school today.
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rayarachelian

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Re: Does anyone have a spare Lisa motherboard?
« Reply #17 on: November 15, 2019, 07:57:27 am »

So how did it go, any further symptom elimination?
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AlexTheCat123

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Re: Does anyone have a spare Lisa motherboard?
« Reply #18 on: November 15, 2019, 02:23:05 pm »

Unfortunately, no. The computer won't power on at all anymore and I am trying to figure out why. I did not really have much time to troubleshoot it yesterday or the day before, but I am going to try and fix it this afternoon. Maybe something is wrong with the power supply? I hope the COP421 isn't dead because I have no idea where to find a reasonably-priced replacement.
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AlexTheCat123

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Re: Does anyone have a spare Lisa motherboard?
« Reply #19 on: November 16, 2019, 08:22:18 am »

I just it powering on again. The trace that caries the PWRSW signal on the I/O board failed and I had to patch it. I tried adjusting the CRT controls on the video board and there was no change, so then I tried probing the audio on the VIA with an oscilloscope. Whenever I turn the computer on or press the reset button on the back, I get a 300-ish hertz signal for about 120ms, then 80ms of inactivity, and another 120ms 300 hertz signal. Then the line remains inactive until I reset the machine. Since the Lisa is supposed to click twice when you turn it on and I got two pulses, it seems like it might actually be somewhat alive. I also tried putting a disk in the floppy drive to see if it would try to read it and I can hear the heads move once or twice and then it goes silent. This makes me think that it is actually trying to read the disk. Do you agree that this probably means that the computer itself is working?
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patrick

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Re: Does anyone have a spare Lisa motherboard?
« Reply #20 on: November 16, 2019, 10:47:16 am »

Beeep-Beeep means memory failure. So now you'll have to check the traces between CPU and memory board.
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rayarachelian

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Re: Does anyone have a spare Lisa motherboard?
« Reply #21 on: November 16, 2019, 05:18:03 pm »

Well, the 68000 is good, so likely most of the CPU board is good, though we don't know if the MMU is good, or the RAM. As Dr. Patrick said, looks like it couldn't read the RAM ( https://lisafaq.sunder.net/single.html#lisafaq-hw-rom_beeps ), so as he said, check the connections to RAM boards, or the pins from the CPU board that go to RAM, maybe swap the RAM boards around as well.

You could try inserting just one memory board in one slot, then turn the Lisa off and move it to the other slot to see if anything changes.

I'm pretty sure it's not trying to boot at this point. The BIOS takes a very long time to test RAM and other hardware before it tries to boot, and even then it usually puts up a menu asking where to boot from (unless the PRAM has a setting that says boot from ProFile/Widget and that hard drive is on and accessible.)

On power on the MMU is in Special I/O space with the boot ROM mapped at address zero and also high memory. It will then do a checksum of the ROM, and beep if it's wrong. Once it finds some RAM, it will go out of SIO space and into MMU context zero, the display will turn on and it will start testing RAM and video memory will be at high RAM.

If there's a fault in page zero RAM where the exception vectors are stored, I think it will fail to show any video and will beep low. In your case you're getting lo,lo tones, so it can't see any RAM.

In terms of the floppy activity, it's more likely that the 6504 CPU which controls the IWM and floppy drive noticed there's a floppy there and initialized the drive which may have spun the motor or moved the heads a bit. But it's certainly not trying to boot yet.

I do see an X/Cops replacement board on vintagemicros for about $100, if it turns out bad, but so far we know it's good enough to power on the Lisa and have the main CPU start and fail the self test. So as long as all the pins and the connection to the mux chip it has are still good, it's likely working. You won't know until you have video if the keyboard and mouse are working. (And if the keyboard isn't working, most likely the foam caps are dead not the COPS on the I/O board.) Most likely any issue around COPS421 functionality is more likely caused by bad traces than by that chip itself going bad. Reflowing solder on its pins will help stop the corrosion too.

I'd replace all the large capacitors in the power supply, even if they're working, chances are they're over 20 years old, more like 35 if they're the originals so many would have failed, or are about to. This won't necessarily fix the CRT issue, but its still worth doing as you're going to have to do it at some point anyway.
However, if the 33V power supply output isn't working due to some caps not working, fixing the power supply will help you get video. This won't happen until it can access RAM, but I think it will still provide power to the CRT and the tube will warm up and glow, and pushing the brightness high should produce a white screen with some horizontal retrace reflection stripes, and since you haven't said you saw those, likely the PS has some issues.

I do see this as well incase you need it: https://www.ebay.com/itm/AMP-60-120-Card-Edge-Connector-Fits-Apple-Lisa-Motherboard/141821714914 - this connector should fit both the I/O and CPU boards.
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AlexTheCat123

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Re: Does anyone have a spare Lisa motherboard?
« Reply #22 on: November 17, 2019, 06:30:31 am »

I am only using one RAM board at the moment because the edge connector on the second one seems to have some corrosion damage, but I will try to fix the connector on the second board and try it out to see if anything changes. I have already checked the traces between the RAM and CPU boards, so I don't think that I have any problems there. As for the CRT, the power supply is putting out the 33V signal as it is supposed to, but the CRT is doing absolutely nothing. Not only is there no video, but there is not even a glow at the back of the CRT and these is no high-pitched whine from the flyback transformer. I also looked at the schematics for the power supply and determined that the video board is supposed to be sending 300V and -100V into the supply, which are supposed to run to the brightness and focus potentiometers on the back, but there is no voltage on either of these lines. This makes me think that something is wrong with the video board itself.
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rayarachelian

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Re: Does anyone have a spare Lisa motherboard?
« Reply #23 on: November 17, 2019, 02:51:35 pm »

I am only using one RAM board at the moment because the edge connector on the second one seems to have some corrosion damage, but I will try to fix the connector on the second board and try it out to see if anything changes. I have already checked the traces between the RAM and CPU boards, so I don't think that I have any problems there. As for the CRT, the power supply is putting out the 33V signal as it is supposed to, but the CRT is doing absolutely nothing. Not only is there no video, but there is not even a glow at the back of the CRT and these is no high-pitched whine from the flyback transformer. I also looked at the schematics for the power supply and determined that the video board is supposed to be sending 300V and -100V into the supply, which are supposed to run to the brightness and focus potentiometers on the back, but there is no voltage on either of these lines. This makes me think that something is wrong with the video board itself.

Ok, incase you don't have it, here's the video board schematic: https://lisaem.sunder.net/cgi-bin/bookview2.cgi?zoom=0?page=24?book=6?Go=Go

One thing that's common is that heat can cause the solder joints on these boards to crack. (or perhaps the corrosion has spread there too) I'd pull it out (careful of capacitors, CRT, etc.) and reflow the solder there, maybe replace some caps.
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AlexTheCat123

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Re: Does anyone have a spare Lisa motherboard?
« Reply #24 on: November 17, 2019, 06:28:16 pm »

Thanks for the schematic! I just removed the video board (which was quite difficult because some of those connectors were really tight) and there do appear to be about 20 questionable looking solder joints on it. I will reflow the whole board and see what happens.
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patrick

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Re: Does anyone have a spare Lisa motherboard?
« Reply #25 on: November 17, 2019, 06:34:01 pm »

There is an auxiliary video output on the back of the machine. That will not work with any known monitor type due to its weird line frequency, but you can check with an oscilloscope whether video is generated at all.

Next step, check both sync signals sent to the video board. Without HSync the flyback circuit is not running, therefore the screen remains dark. Nevertheless you should see the heater glow, it is getting 12V directly from the PSU.

Check all supply voltages for ripple. Replace capacitors if the ac component is too high, but leave them alone when ripple is still in spec. Electrolytic capacitors from the '80s sometimes fail, but most of them are still in excellent condition today. Parts from the '90s are much worse (leaking etc), and today's stuff lasts exactly until your warranty has expired.

Best idea: find someone living close to you who is able to check your I/O, CPU and RAM boards with his/her machine. Then you can be sure that all issues are located on the mainboard or video section.
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AlexTheCat123

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Re: Does anyone have a spare Lisa motherboard?
« Reply #26 on: November 17, 2019, 07:42:23 pm »

I reflowed the entire video board and I get something on the display now! The first time I turned it on after the reflow, the screen was bright and it displayed an error code of 49. The second time, there was no error code. The third time, however, the screen started out bright and suddenly dimmed to the point that I can barely read it, even with the lights off. I played with all of the potentiometers, but I can't get it any brighter. What happened?
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rayarachelian

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Re: Does anyone have a spare Lisa motherboard?
« Reply #27 on: November 18, 2019, 01:00:38 pm »

I reflowed the entire video board and I get something on the display now! The first time I turned it on after the reflow, the screen was bright and it displayed an error code of 49. The second time, there was no error code. The third time, however, the screen started out bright and suddenly dimmed to the point that I can barely read it, even with the lights off. I played with all of the potentiometers, but I can't get it any brighter. What happened?

So 49 is not a good thing, it indicates A or F line trap, this shouldn't ever happen with just a plain boot ROM - might happen if it tried to boot off a hard drive with bad code on it, but not from the ROM, so there might be issues somewhere else on the CPU board, or the ROM is bad. You did say you have a scope, right, you might want to hook it up between the normal +5V and GND rails on the CPU and see if the 5V line is clean or if it drops out or is noisy - this would indicate power issues - though there should be a filtering cap near the CPU to prevent that. You shouldn't be randomly seeing A or F line errors like that. Something is up with the CPU board still. I'd guess maybe it's a contact that's still marginal from the motherboard corrosion and unlikely to be power, but who knows.

It's also possible that something on the analog video board just burned out, but keep power cycling it after waiting a few hours to allow the caps to drain and see if it comes back or not. If it comes back, it's likely a marginal capacitor. It could be as simple as one of the trimpots, or the brightness control in the back not making good contact, they do go bad over time or wear out.  Could also be that one of the fixed cracked solder joint cracked again or a trace is somewhat broken and moving the board fixed it, but heat expansion from being on caused it to separate again. Could also be a transistor that's being used as a brightness amplifier gave out?
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Lisa2

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Re: Does anyone have a spare Lisa motherboard?
« Reply #28 on: November 18, 2019, 05:34:59 pm »

I reflowed the entire video board and I get something on the display now! The first time I turned it on after the reflow, the screen was bright and it displayed an error code of 49. The second time, there was no error code. The third time, however, the screen started out bright and suddenly dimmed to the point that I can barely read it, even with the lights off. I played with all of the potentiometers, but I can't get it any brighter. What happened?

A common failure point for the Video board, is the 7824 voltage regulator at U1.  Usually when it goes it cooks the 120 Ohm resistor R1 near the R2 (width) pot.  Look closely at R1 and see if it's is discolored ( you can see R1 without removing the board ).  If U1 is bad there will be no power to the flyback transformer..

Rick


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AlexTheCat123

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Re: Does anyone have a spare Lisa motherboard?
« Reply #29 on: November 18, 2019, 08:29:15 pm »

Success! I found a few solder joints on the video board that I forgot to reflow and I also found a few more traces that I forgot to patch on the CPU board. I now have a bright and stable picture and the Lisa shows the TESTING... screen and puts checkmarks over all of the components. However, I feel like it completes the test a bit too fast. It gets through the entire test in about 10 seconds, which seems a bit too fast, even though I only have 512K of RAM installed for it to test. It does not show the ROM version in the corner of the screen like I think it is supposed to. After this, it goes to the Startup From... menu and I can use the mouse to select an option. However, it displays two floppy drives in the menu, even though I only have one. If I select the second drive, it attempts to boot from disk and then promptly ejects the disk since there is nothing on it. The weird part is that it shows a picture of a Twiggy disk with an X over it along with the Error 23 (disk not readable) instead of a 3.5" disk.  Given these strange occurrences, do you guys think that I have the wrong ROMs installed? They do have a handwritten marking on them that looks like a C, which makes me think that these are revision C ROMs that only work with Twiggy drives.
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