Print

[bmwcyclist]

I bought a spare working CPU card.

When I first got it, I got nothing on power on.

I put in a new CPU and got a 42 CPU card error.

I replaced the master video rom, but no change.

Any suggestions?

[AlexTheCat123]

Do you have your XLerator installed? If so, then this error is to be expected if the CPU board is fitted with anything other than 3A ROMs. It's simply because the XLerator messes up the timings that the CPU board needs in order to read the system serial number out of the VSROM. But the 3A ROMs remove this check, so you don't get the error anymore when using them. If you do indeed have the XLerator installed, then just ignore the error; it's not a problem at all!

[bmwcyclist]

Do you have your XLerator installed? If so, then this error is to be expected if the CPU board is fitted with anything other than 3A ROMs. It's simply because the XLerator messes up the timings that the CPU board needs in order to read the system serial number out of the VSROM. But the 3A ROMs remove this check, so you don't get the error anymore when using them. If you do indeed have the XLerator installed, then just ignore the error; it's not a problem at all!

Thank you for the reply!

I am sorry I should have been more clear about the configuration. I am trying to do this on breaks from work, and my head is crowded.

I have obtained 2 spare CPU boards and bought ASIS untested. The goal is to not have to remove and replace the CPU chip and the XLerator if I want to troubleshoot or run LOS etc, and sell off the spare board to attempt to recoup some $$.

One of the spares is working great! the other one is the one I am troubleshooting.

When I got the spare when I installed the board I got nothing (black screen)

I replaced the CPU chip and got the 42 error. From what I could find this error can be related to video so I replaced the VROM.

No change.

So that is where I am at.

I would really like to get this board going so I can sell it to offset my Lisa project debt.

[sigma7]

... got the 42 error. From what I could find this error can be related to video so I replaced the VROM.

Since it has been established there is no XLerator installed, and assuming you're using ROM version H or earlier...

Looking at http://bitsavers.org/pdf/apple/lisa/firmware/Lisa_Boot_ROM_Asm_Listing.TEXT, it seems error 42 is returned when either the vertical retrace interrupt is not working, or the serial number cannot be read (eg. search for VIDERR ).

Assuming the video is working correctly, I think the only failure that will be easy to detect and resolve is if the socket has a bad connection to pin 14 of the Video PROM (where the serial number data stream is emitted). To investigate this, check that there is low resistance between pin 14 of the Video PROM chip and R8.

You could perform some of the ROM's tests manually using service mode to see which one of the possible errors is the cause, but that will only be a small help in locating the actual failure and part(s) to replace. Hence the recent topic regarding inexpensive logic analyzers; doing the investigation with a voltmeter or oscilloscope is possible but will be time consuming and laborious.

[bmwcyclist]

R8 - 151ohm.

VROM pin 14 to R8 close side I have connectivity with no resistance

VROM pin 14 to R8 far side I have 151 ohm.

Could I have 2 bad VROMs? both have stickers on them, so I assume they are burnable?

[sigma7]

R8 - 151ohm.
VROM pin 14 to R8 close side I have connectivity with no resistance
VROM pin 14 to R8 far side I have 151 ohm.

Those readings are correct, so no problem there.

Could I have 2 bad VROMs? both have stickers on them, so I assume they are burnable?

You could have a bad one, but they aren't a typical cause of failure. If you did have a bad one (or installed a PROM that is not a video PROM), the video display is likely to fail.

The Video PROMs are "One Time Programmable". They can't be erased and reprogrammed.

These are bipolar fuse programmable parts. They have literal fuses in them that are blown open during programming in the desired pattern. The fuses can't be restored. Although one can blow additional fuses, that's not usually what's needed.

(Some other OTP parts are actually EPROMs in windowless packages to save the expense of the windowed package; they potentially could be erased by x-rays or something like that, but the video PROMs are not like those. The Lisa doesn't have any of those.)

So you'll need to do more detailed troubleshooting... are you interested in purchasing an inexpensive logic analyzer or can you borrow one?

[bmwcyclist]

Those readings are correct, so no problem there.

Ok, thanks!

You could have a bad one, but they aren't a typical cause of failure. If you did have a bad one (or installed a PROM that is not a video PROM), the video display is likely to fail.

I tried the known good one from my other board and no change so its not the VROM.

So you'll need to do more detailed troubleshooting... are you interested in purchasing an inexpensive logic analyzer, or can you borrow one?

My friend is going to give me his unfinished Vintage Chip Tester kit. But if you think that is barking up the wrong tree, then yes, I will need to buy one.

.

[sigma7]

My friend is going to give me his unfinished Vintage Chip Tester kit. But if you think that is barking up the wrong tree ...

I think it is very unlikely the chip tester will help you figure out which chip to test, and you won't want to de-solder more parts than you have to, so IMHO that is not the place to start. But someone else may have another approach in mind... anyone?

A couple of other simple tests that may or may not give clues:

1) When you get error 42, if you "continue", can you boot into MacWorks and if so, does it operate correctly?

2) If you have a set of 3A ROMs + the video PROM for the square pixel screen modification kit... if you install those on the problem board, does it still give error 42? Since those don't have a serial number, error 42 would only be generated by a vertical retrace interrupt fault.

3) If you side-by-side compare the bad board with a good one, is there any visible evidence that the bad board has had any damage (repaired or not), or any parts replaced?

4) I don't know how much tolerance there is in the serial number timing, but I wonder if the crystal Y1 (near coordinates F1) was replaced with something not sufficiently close to 20 MHz... is it stuck to the bad board the same as on the good board?

5) The new 68000 CPU you installed in the previously dead board... if you put that CPU in the good board, it works and does not generate error 42, correct?

edit: added #5

[bmwcyclist]

1) When you get error 42, if you "continue", can you boot into MacWorks and if so, does it operate correctly?

No.

I made a video that includes the startup tone and a walk-through of trying to boot.

https://youtu.be/GJHmPptvQhc?si=y2Up7WxvseUwC9oT

2) If you have a set of 3A ROMs + the video PROM for the square pixel screen modification kit... if you install those on the problem board, does it still give error 42? Since those don't have a serial number, error 42 would only be generated by a vertical retrace interrupt fault.

I only have H ROMs

3) If you side-by-side compare the bad board with a good one, is there any visible evidence that the bad board has had any damage (repaired or not), or any parts replaced?

The board looks pristine (see attached photos) except for some scratches on the small capacitors bodged on one of the chips (see attached photo)

4) I don't know how much tolerance there is in the serial number timing, but I wonder if the crystal Y1 (near coordinates F1) was replaced with something not sufficiently close to 20 MHz... is it stuck to the bad board the same as on the good board?

It appears to be original but has no freq numbers that I can see. (see attached photo)

5) The new 68000 CPU you installed in the previously dead board... if you put that CPU in the good board, it works and does not generate error 42, correct?

I am loath to pull and swap the CPU out of the good board. From a previous discussion here, I learned that the CPU sockets can fail after repeated use, and I don't know how much use these used boards have already had.

I do have a 3rd CPU, new and unused, which I can try.

[stepleton]

I'm sorry I don't have the time to pitch in to this diagnostic session --- I've got a lot on my plate at the moment. But here's a remark about the Retro Chip Tester Pro:

I have one, and I love it --- it's a wonderful device as well as a fun kit to assemble. What's become clear to me in using it, though, is that you can only really trust it if it says that a chip is bad.

The RCT Pro will tend to exercise a chip pretty well. But I suspect it will do this with voltages that (for TTL at least) are well within the band of legitimate TTL signal voltages and not something closer to the margins. It will also only change a chip's inputs at a certain frequency or within a certain frequency range. Both of these testing conditions may differ from the operating conditions for the IC, which the computer may drive at higher frequencies or with signals that are not as well-formed as the ones the tester uses. If the IC is marginal, in other words, the tester may not catch it. Therefore, a chip that tests well may still be too broken for the computer you want to use it in.

On the other hand, if the RCT Pro says that an IC is bad, then in my experience it is either really broken or at least too marginal for anything I'd like to use it for.

I don't regret getting the tester for a second, but as far as detecting problems goes, be prepared for the thing to yield a fair number of false negatives.

[bmwcyclist]

stepleton, Thank you! Excellent review and great to know.


I NOW HAVE THE BOARD WORKING!! 

I found my mistake.

The CPU I bought was not what I received. I asked for a MC68000L10 but it is a MC68010L10.

I put in a new MC68000L8 and now it is working great!!

Anyone want to buy a good working CPU board???

Thank you for your help everyone! If it were not for the suggestion to swap the CPU again I would have not caught my mistake for some time.

I am going to let it run all day with a screen saver or something, play some games, maybe draft an article tomorrow, to let it burn in and make sure it is trustworthy before I try to sell it.

[jamesdenton]

Good catch!

Also relevant: https://lisalist2.com/index.php/topic,43.msg159.html

[sigma7]

For posterity... with the 68010 installed, after error 42, continuing to try to boot MW+II from the parallel port hard disk results in error 75 after "Hold down space bar or mouse button to adjust startup configuration".

I made a video that includes the startup tone and a walk-through of trying to boot.

https://youtu.be/GJHmPptvQhc?si=y2Up7WxvseUwC9oT

Given that fakes, counterfeits, and "re-marked" salvage chips are around, if you see this behaviour with a part marked 68000, then I'd guess it is actually a 68010.

Also beware when ordering by part number that there is a Motorola 6800 processor (in a smaller package), the Lisa uses the 68000. The speed of the CPU board is just over 5MHz, so speed grades 6,8,10,12, and 12F will work.

edit: added 6800 & speed grade info

[bmwcyclist]

Good catch!

Also relevant: https://lisalist2.com/index.php/topic,43.msg159.html

You got the good catch, I didn't get a FISH! 

[bmwcyclist]

. The speed of the CPU board is just over 5MHz, so speed grades 6,8,10,12, and 12F will work.

12F ?

Foxtrot?

What does the F get you?