Odd ROM (SE/30)

[Cosmo]

Am i missing something here? I'm not so familar with ROM's...

From : http://home.earthlink.net/~gamba2/os8_se30.html

IC part numbers:342S0654-A

342S0653-A

342S0652-A

342S0651-A

IC package: PLCC-32

ROM base: 27C512

ROM type: OTP EPROM ( 64K X 8 )

These do match by codes (memory modules).

The ROM i have also reads - 820-0244-01 and ASSY 630-4333 and silk printing "512K ROM SIMM-32" - Apple Computer © 1988

So this is an 512k ROM for SE/30? How come so, it shipped with 256k ROM? Can't be so. Must be IIx or IIcx etc??

 

[Dennis Nedry]

The best way to tell is to run GetROM on this Mac and then open the ROM file that it produces with a hex editor. The first 8 hex digits of the file can be compared with a list of Mac ROM checksums. This will tell you exactly all of the Macs that came with your ROM.

 

[8bitbubsy]

My SE/30 motherboard came with a ROM that has the text "512kB" on it too. :O

I'll run GetROM on it now and find out the checksum of the ROM.

EDIT: Oh, it got dumped as a 256kB ROM. The ROM checksum is 0x97221136.

A normal SE/30 ROM indeed.

 

[Dennis Nedry]

It could be that the circuit board is printed to support 512kB of ROM but only 256kB of chips were installed.

 

[Cosmo]

Must be so. That makes most sense. I'll try that on my SE/30 motherboard when i find and working body SE or SE/30, mine's analoque board is toasted for good.

I took an Macintosh IIx this morning to parts and there were an SIM, similar but different code on it. I'll see what's the codes on it.

Only one of the IIx's i had, did have the ROM, others did not. Those all went to trash.. only case and motherboard on them, some leaked.

Could not keep them at work anymore, taking too much space in the server corner.

I really want an working SE/30! } :simasimac:

 

[uniserver]

tomarrow i was going to throw this in my SE/30, its from a IIsi i guess im parting out, will the old rom i'm taking out of the se/30 work in the IIsi?

 

[nvdeynde]

Must be so. That makes most sense. I'll try that on my SE/30 motherboard when i find and working body SE or SE/30, mine's analoque board is toasted for good.

What's wrong with your SE/30 Analog board ?

As long as it's not the flyback, it can probably be repaired unless the PCB is severly damaged of course...

I'm in the middle of recapping the analog boards and PSU's of my SE series now.

I already did my older Compact Macs ( 128K to Plus ) last year.

One must not forget that the capacitors on the Analog board and PSU are as old as the one's on the logic boards.

When I recapped my analog boards I discovered several large radial caps that were dried out, some leaked a little at the bottom.

In the end they are over 22 years old so I guess it's time to replace them.

 

[trag]

It could be that the circuit board is printed to support 512kB of ROM but only 256kB of chips were installed.

I believe that the "512K" actually refers to the capacity of the memory chips on the SIMM. The SIMM is layed out to accept up to 512Kbit PLCC-32 memory chips. Four 512Kbit memory chips gives one 256Kbytes of capacity.

The PLCC-32 package which the ROM/OTP EPROM/EEPROM/FLASH (non-volatile memory) chips come in have their pinout defined by a JEDEC standard.

The standard pinout for the PLCC-32 package changed significantly between the 512Kbit capacity non-volatile memory chips and the 1Mbit chips.

So, a SIMM which will take the 512Kbit and earlier has one pinout (connections) for the 512Kbit chips. A SIMM which will take 1Mbit and larger memory chips has a pinout with substantial differences from a board built for 512Kbit chips.

This is why we couldn't just take old SE/30 ROM SIMMs and replace the ROM chips on them with newly programmed Flash chips. The pinout on the SIMM for the PLCC-32 chips is wrong for the larger capacity memory chips. So Doug had to lay out a whole new board which would provide the proper pinout for the larger memory chips.