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HP 3325A ROM Replacement

Max Frister All Messages By This Member #73576 I thought I would summarize a somewhat meandering thread. I’ve received the Artek manual and it is great!? It appears I do have a failing ROM IC.? As time went by HP changed from 4 4k8 chips to 2 8k8 chips and there is a way to jumper some boards to tell it which is installed.? (Joe: is that just the A/B jumpers near U5, or is it more than that?).? Apparently there are even some 3325a’s with 3 ROM ics. The HP nano-processor only has 11 address lines for a 12 bit space and so they played games to extract the 12 bit.? In the 4-chip solution, each chip has 2 select pins which are used in such a way as to provide the top 2 most significant bits. Thus far, I have not found a 4k8 EPROM or EEPROM that is pin-compatible with the original Synertek Sy2332/Motorola MCM88A332 masked ROM.? The TMS2532 are almost right, but lack the second select pin. [I keep seeing this listed even in historical literature as pin-compatible, but it is not according to the data sheets.? I’ve seen this so many places that I wonder if the datasheets are wrong and pin 20 can be used as a second select.] The original 2-IC solution used the Motorola MCM68764C EEPROM.? A later version of that chip? is the Motorola MCM68766.? Joe has previously extracted the 2-IC ROM program.? I would guess that the 4-IC data is the same, just split between chips.? I also think the data is the same independent of options as otherwise the signature analysis info would have to change between machines, and it does not. My repair options include: 4 IC’s.? This looks to require some extra glue logic to decode the second select unless a pin-compatible EEPROM can be found.? It would also require me to extract my data or split the existing 2-IC data. 2 IC’s.? This only requires some jumper changes and the ROM program is already available. 1 IC solution.? Because the 3325a already decodes the 2 select pins as if they’re address pins, this would only require a simple pin-remapping board for the new IC. Option B looks like the obvious choice except that I have so far only been able to find used replacement EEPROMs and I wonder about the longevity of those. I’d also like to help the next person that needs to fix the ROM in a 3325a, and that argues for Option C.? Once option C is chosen almost any parallel ROM can be used and I’m seeing some flash-ROM with a listed lifetime of 100+ years. Does anyone have a favorite 16k8 EEPROM ic that is common and likely to be available for a few more years?
Tom Miller #73598 ? Either a 27C128 or a? 1/2 of a 27C256 would do it. A small PC board with some pins to match one of the four 4k sockets as well as some chip select jumper(s) to the other socket(s). Both of these chips are supported by most programmers and the supply should persist. ? This may be useful for many other equipment that used the same Roms. ? I repaired a HP DMM that had Mostek Roms by installing a 24 pin socket in one position and installing the 27C128 with the four pins bent out and wired to the other sockets. ? ? ? toggle quoted message Show quoted text ----- Original Message ----- From: maxfrister@... [hp_agilent_equipment] To: hp_agilent_equipment@... Sent: Tuesday, February 16, 2016 8:00 PM Subject: [hp_agilent_equipment] HP 3325A ROM Replacement ? I thought I would summarize a somewhat meandering thread. I’ve received the Artek manual and it is great!? It appears I do have a failing ROM IC.? As time went by HP changed from 4 4k8 chips to 2 8k8 chips and there is a way to jumper some boards to tell it which is installed.? (Joe: is that just the A/B jumpers near U5, or is it more than that?).? Apparently there are even some 3325a’s with 3 ROM ics. The HP nano-processor only has 11 address lines for a 12 bit space and so they played games to extract the 12 bit.? In the 4-chip solution, each chip has 2 select pins which are used in such a way as to provide the top 2 most significant bits. Thus far, I have not found a 4k8 EPROM or EEPROM that is pin-compatible with the original Synertek Sy2332/Motorola MCM88A332 masked ROM.? The TMS2532 are almost right, but lack the second select pin. [I keep seeing this listed even in historical literature as pin-compatible, but it is not according to the data sheets.? I’ve seen this so many places that I wonder if the datasheets are wrong and pin 20 can be used as a second select.] The original 2-IC solution used the Motorola MCM68764C EEPROM.? A later version of that chip? is the Motorola MCM68766.? Joe has previously extracted the 2-IC ROM program.? I would guess that the 4-IC data is the same, just split between chips.? I also think the data is the same independent of options as otherwise the signature analysis info would have to change between machines, and it does not. My repair options include: 4 IC’s.? This looks to require some extra glue logic to decode the second select unless a pin-compatible EEPROM can be found.? It would also require me to extract my data or split the existing 2-IC data. 2 IC’s.? This only requires some jumper changes and the ROM program is already available. 1 IC solution.? Because the 3325a already decodes the 2 select pins as if they’re address pins, this would only require a simple pin-remapping board for the new IC. Option B looks like the obvious choice except that I have so far only been able to find used replacement EEPROMs and I wonder about the longevity of those. I’d also like to help the next person that needs to fix the ROM in a 3325a, and that argues for Option C.? Once option C is chosen almost any parallel ROM can be used and I’m seeing some flash-ROM with a listed lifetime of 100+ years. Does anyone have a favorite 16k8 EEPROM ic that is common and likely to be available for a few more years?

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