General Category > Lisa Troubleshooting and Repair

CPU 42 error...

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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:

--- Quote from: AlexTheCat123 on March 21, 2025, 10:04:00 am ---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!

--- End quote ---

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:

--- Quote from: bmwcyclist on March 21, 2025, 10:21:12 am ---... got the 42 error. From what I could find this error can be related to video so I replaced the VROM.

--- End quote ---

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?

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