General Category > Lisa Troubleshooting and Repair
Help please for my Lisa 2/5
AlexTheCat123:
It's great that you have clock and reset! When you say that reset goes low when you push the reset button, I'm assuming that it goes high again around a second later, right?
--- Quote ---If that looks good, try probing Q0-Q3 on the LS161 at U7A. This counter chip provides the state sequences that control the operations within the floppy controller: This is a bit beyond my skill set, but signals q0-q3 do show square waves of various duty cycles. I assume it's what you'd expect ?
--- End quote ---
Yep, that sounds about right. Each one of those pins should have a square wave of a different frequency on it!
--- Quote ---Also go through and probe all of the address and data lines on the I/O board ROM to make sure that they all have activity on them: there is NO activity that I can see. Would this help us ?
--- End quote ---
Well, that's a big problem! You've already confirmed that Q0-Q3 on U7A are producing square waves as they should, but now maybe try probing pin 27 (PHI0) on the 6504 to make sure that the signal from Q2 on U7A is actually getting to the 6504 to clock it. If it is, then you might have a bad 6504. Assuming it's getting reset at power-on and it's being clocked correctly, you should be seeing activity on the bus, even if there are still serious problems somewhere else in the floppy controller circuit. I guess you could also have a bad EPROM (or one of the other chips connected to the bus) that's pulling those lines to 5V or ground, but that's probably pretty unlikely. Do you have a spare 6504 (or a 6507 from something like an Atari 2600) that you could swap in? That's probably what I'd try next!
pintoguy:
Thanks Alex. Please see my replies.
When you say that reset goes low when you push the reset button, I'm assuming that it goes high again around a second later, right? Yes
try probing pin 27 (PHI0) on the 6504 to make sure that the signal from Q2 on U7A is actually getting to the 6504 to clock it: Yes, I get Q2 on pin 27
I guess you could also have a bad EPROM that's pulling those lines to 5V or ground: I checked every pin on the 6504, and only get the 5V at pin4 and ground at pin2, which I think is normal
Do you have a spare 6504 that you could swap in? Yes I do (from a working 2/10). It doesn't help
Should I look for an EPROM replacement ? Is this IO ROM re-burnable ?
blusnowkitty:
--- Quote from: pintoguy on August 07, 2023, 04:22:21 pm ---Should I look for an EPROM replacement ? Is this IO ROM re-burnable ?
--- End quote ---
The ROM can be reburned or replaced easily, it's a standard 27(C)16. ROM images are up on Bitsavers.
pintoguy:
Thanks. I haven't had a chance to do much in the past few days, but here is the latest:
1) The IO ROM placed in a good IO 2/10 board does display the proper H/A8 ROM codes. Is still shows error 57, but I think it's normal (2/5-2/10 floppy controller mismatch ?)
2) I actually have sporadic activity on the data lines of the IO ROM that comes and goes. But even when I see activity, I still have the error 57 issue
3) I tried to boot without the IO ROM chip in, and get exactly the same error
4) Then at some point, the board stopped working completely, and my 2/5 now boots with just the gray screen, with the CPU ROM letter "H" on the screen
I know the integrity of the gold pad from the edge connector J1 is important. They were quite corroded, and I cleaned them and coated them with solder as best as I could, but they still show missing areas. As far as I know, they still make good contact, but perhaps I should put some new copper strips on these pads. Any suggestion for what to use and how ?
Thanks
sigma7:
--- Quote from: pintoguy on August 10, 2023, 11:50:54 am ---I know the integrity of the gold pad from the edge connector J1 is important. They were quite corroded, and I cleaned them and coated them with solder as best as I could, but they still show missing areas. As far as I know, they still make good contact, but perhaps I should put some new copper strips on these pads. Any suggestion for what to use and how ?
--- End quote ---
I suggest checking any questionable circuits that pass through the card edge using an ohmmeter with the card plugged in. (eg. measure from a part on the I/O board to the bottom of the motherboard or a part on some other board.)
A durable repair of a card edge finger takes some extra care and if there are multiple pads to replace that's probably a big job.
The pads are epoxied in place, but to maintain the board thickness (to prevent damaging or deforming the socket), you probably need to grind a recess in the board where the pad will go to make room for the epoxy. You can then gold-plate a copper pad with a simple kit, or use an already gold plated pad removed from a donor board. Note that card edge fingers are plated with a different (more durable) gold alloy than the gold that covers all of some modern boards, so I suggest using a scavenged card edge finger for the repair.
Since you may be troubleshooting further corrosion problems on that board, another option is to populate a bare board (either with new parts or moving parts from the defective board) ... I believe the Sapient Technologies boards are available (or will be soon) as bare boards from John / VintageMicros.com
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