Mac IIcx death startup chime after recapping

[Pitou]

Hello,

I just recapped a Mac IIcx and it now turns on, but I get the death startup chime.

I was looking at the board and there is nothing at D1 and D2. Does it need diodes there?

If so, what value/number?

Any other idea?

Thank you.

Pitou!

 

[Pitou]

Update:

After installing a ROM SIMM coming from a IIfx and removing jumper W1, I get the normal/good startup chime.

Should I look at the soldered on-board rom chips (there are 4) or could it be something else around?

Any pointers?

Thank you

Pitou!

 

[Pitou]

I just find this on this website:

http://macfaq.org/hardware/logicboard.shtml

It has been speculated that the early-production IIcx and IIsi models may have had an error in their onboard ROMs and the ROM SIMM is required to correct this error. On later models, it was removed because the error was fixed, and this is the reason for the rarity of the ROM SIMMs on these two models.

Could this be related? Does this error prevent the Mac from starting up?

I might plan to desolder the 4 rom chips and read them.

I guess that any EEPROM 64k x 8 could replace the existing one. Am I right? Can you suggest any EEPROM number that will do the job?

Thank you.

Pitou!

 

[Pitou]

FYI,

I desoldered the 4 rom chips and read them.

By comparing them with good known ones, I found that on the 4th rom (342-0642- B) , 1 byte is different at offset $AD95. $8A instead of $AA.

All 3 others are fine. I also read the 4th rom 3 times just to make sure.

I have a spare 0642 rom. I will install sockets and try it.

Will keep you posted.

Pitou!

 

[Pitou]

Success! The culprit was the 4th rom (0642) as expected. Now I'm wondering if that is the error on the early production and I simply have a bad rom.

Pitou!

 

[Pitou]

I meant "or" I simply have a bad rom

 

[alexGS]

Success! The culprit was the 4th rom (0642) as expected. Now I'm wondering if that is the error on the early production and I simply have a bad rom.

Pitou!

I just wanted to say - thanks for documenting this, it hadn’t crossed my mind that the IIcx I’m working on would have a bad ROM - I’m going to borrow the ROM SIMM from a IIfx to test. I’m particularly impressed that you went to the trouble of desoldering and reading out the ROMs!