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[pintoguy]

Thanks. One repair that I used for some very badly damaged pads was to hammer down a thin copper wire on an anvil, until  it became a thin strip. I them soldered that strip to the old pad. Not the cleanest way to proceed, but it did work OK, with minimal thickness increase.

And yes, I communicated with John (vintagemicros) but he does not have 2/5 IO bare boards in stock. I might go the AlexTheCat123 github route, just like I did with the MB

[sigma7]

I communicated with John (vintagemicros) but he does not have 2/5 IO bare boards in stock.

Perhaps that was a miscommunication or a while ago... moments ago John confirmed that he does have some in stock now (unless I misunderstood).

[pintoguy]

Perhaps that was a miscommunication or a while ago... moments ago John confirmed that he does have some in stock now (unless I misunderstood).

This was 2 weeks ago. Perhaps he understood I wanted to finished board. I'll ping him again. Thanks

[sigma7]

The ROM can be reburned or replaced easily, it's a standard 27(C)16. ROM images are up on Bitsavers.

There are also the relatively recent 400k/800k "universal" variants in the files section: Lisa I/O Board ROMs

IIRC, the I/O Board EPROMs are 2732; the expansion boards' are 2716 (there are a couple of exceptions).

[pintoguy]

This week's update: Looks like the EPROM is OK. It reads and verifies the 341-0290-B BIN file perfectly. So I think we can put this to bed.

I noticed that +5B only reads 4.8V or so, when +VSTBY is 5.5V. On my "good" board, it's 5.3V. So I suspected that diode D9 was therefore bad, but after I changed it, I still have the problem.

But..., chip 8T97 at U1F is very hot to the touch, when it's perfectly cool on my good board. I had told Alex that it was an LS367, but I was wrong, as I simply read what's written on PCB. I'll trace the signal around that and see what happens, but I hope I have found the culprit.

[sigma7]

I noticed that +5B only reads 4.8V or so, when +VSTBY is 5.5V. On my "good" board, it's 5.3V. So I suspected that diode D9 was therefore bad, but after I changed it, I still have the problem.

Note that +5B2 is different from +5B, they both are derived from +5STBY, but through different diodes.
+5B2 is via D9, which is an ordinary silicon rectifier, so a 0.7V voltage drop is not surprising.
+5B is via D3, a Schottky diode, so the drop should be less than 0.7V, making +5B higher.

So if +5B is indeed 4.8V; D3 is the suspect.

But I'd guess it doesn't matter because digital. To me, it looks like +5B2 only exists as a separate circuit to decrease the load on the battery, which drives +5B when power is disconnected.

chip 8T97 at U1F is very hot to the touch

U1F drives the long ribbon cable that goes to the floppy; try disconnecting the lite adapter and see if U1F runs cool. If so, then look for a problem with the Lite Adapter, floppy drive, or cabling.

U1F also drives /DTACK when the CPU accesses the FDC SRAM, so if the 8T97 is not working, the effects would line up with the symptoms you've reported.

[pintoguy]

Thanks sigma7. Yes, I misspoke, it is +5B2 that shows the .7V drop. And thanks for explaining the nature of these +5B and +5B2 lines. I was scratching my head on this for many days, but it makes a lot of sense now. B would stand for "battery" perhaps ?

And as I was tinkering around U1F, the system died. Upon turning on, the switch light turns on for a second or so, before shutting off. I suspect a short perhaps ? Might be consistent with the hot U1F chip that gave up? I have spare 8T97's ordered, so will update hopefully in a few days.

Thanks again

[sigma7]

Upon turning on, the switch light turns on for a second or so, before shutting off. I suspect a short perhaps ? Might be consistent with the hot U1F chip that gave up?

Removing U1F will allow you to confirm that it is the problem. With U1F missing, the signals driving the Lite Adapter/Floppy drive will be missing, as will /DTACK generated when the 68k accessed the FDC shared RAM. So startup should go normally until the point where the self-test checks the FDC, which won't respond, causing an I/O Board error.

The 74LS367 has the same function as the 8T97, but with less output current. If you have those on hand, you could try one in place of the 8T97 while waiting for those to arrive, leaving the Lite Adapter unplugged or bending out the floppy signal output legs of the chip so they don't make contact with the socket. The drivers of /DTACK elsewhere in the Lisa are not 8T97s, so the LS367 may be adequate for driving /DTACK here (but likely not for the floppy signals).

HTH, James

[pintoguy]

Thanks James. The five 8T97 arrived today, so I'll report shortly, after I get a chance to go back to the bench.

[pintoguy]

Bad news today. I removed the 8T97, and the "short" is still there. I call it "short" because I think the symptoms (turns on for ~1 second and switches off) are consistent with it. But is it ? Any input would be greatly appreciated. I think I remember reading about these same symptoms earlier, but cannot find the post

What I know now is that it's not the PS, nor the COP421, nor any of the other socketed chips.

[Lisa2]

Will the system stay on if the I/O board is removed?  This may tell you if the issue is on the I/O board or elsewhere in the system.

[pintoguy]

If I insert the board from a good 2/10, the light stays on. This is why I almost certain it's the IO Board

[sigma7]

... almost certain it's the IO Board

Check the socketed chips for one in backwards (happens to all of us).

On the questionable I/O Board (out of the Lisa), check the resistance from +5V to ground, and from +12V to ground. If either of those are nearly shorted, the PSU will click.

Depending on the sensitivity of your ohmmeter, you may be able to locate a short within a few chips... keep moving the probes around until you find the area where the resistance (eg. from +5 to ground) is the least.

IIRC, this is a battery corrosion repaired board... visual check for further corrosion?

[pintoguy]

Thanks very much James

Check the socketed chips for one in backwards (happens to all of us).

Yep, all OK. I even removed them all - same result

On the questionable I/O Board (out of the Lisa), check the resistance from +5V to ground, and from +12V to ground. If either of those are nearly shorted, the PSU will click.

800 Ohm or so for +5V-gnd and 4Mohm for 12V-gnd, so OK I guess ? I didn't check the -5V though. My PS actually does not click. The power just shuts off after one second or so. So perhaps not a short ?

IIRC, this is a battery corrosion repaired board... visual check for further corrosion?

Yeah, I'm almost sick of looking at the board and checking all the traces after 2 month of that  . But I'll persevere

[sigma7]

800 Ohm or so for +5V-gnd and 4Mohm for 12V-gnd, so OK I guess ?

4 MegOhm isn't right, way too much resistance -- I'd guess you didn't get the right test point or a good connection. On a sample here, +12V to ground is about 59 KOhm. +5 to ground is about 500, close enough to yours that I'd not suspect it.

My PS actually does not click. The power just shuts off after one second or so. So perhaps not a short ?

Ah yes: no. If there is a short, the PSU will click as the over-current protection kicks in, then resets, repeatedly. No clicking very likely indicates the problem is not a short.

Presumably then the COPS power control circuit is telling the PSU to shut off.

Refer to sheet 2 of the 5 page schematic...
Check the ON signal at U7F-12.
If it is low, then that will turn off the power.
I see that "ON" is pulled up by R42 to "+5B2" which came up earlier, so re-check that +5B2 is roughly 5V.
Presuming that "ON" is low and +5B2 is around 5V; pushing the power switch should make "ON" go high... does it go high briefly or stay low?
Depending on what you find, work back through the circuit to the COPS and see if it is generating the ON state or not, and/or see if some other part of the circuit is over-riding that.