HP34C Chips positions ?



#7

Hello,

I've opened my HP-34C for contacts cleanning and didn't note the 3 small chips placement... and mix them up.
Stupidly I :-(
Anyone could help me to figure them out which goes where.

Looking at the back, I guess something like ?

ILB902/80402/SGP02 (up) IMA10015/1215/SGP804 (center)
IMA114/80382/SGP14 (bottom)

Please help,
Thanks,
Pyerre


#8

Hi;

I had a look at this photo and it seems to me that, except for the eightieth pin of the topmost IC, all three IC's share the same connections, say, it doesn't matter their position; just check for the topmost and pin #1 reference. I'd also use a multimetter (lower ohm scale, flex without IC's) and check it there is no internal connection for this particular pin and the others. Who knows...

Anyway, compare your flex PCB with the one in the picture. Better yet, look at your calculator's flex and check for the connections.

Hope it helps.

Regards.


#9

Two of the chips (ROMS) share the same pinouts, the third is the RAM chip that has a different backup power supply connection. Or it could be two RAMS and one ROM. The two common pinout chips can be swapped, the other can't. I don't have a 34C handy to say which chips are which though.


#10

Hi;

I believe you're right about ROM's and RAM, mostly because the separate IC has its poer pin comming straight from the power supply connector, and the others share their power pins with the CPU. I guess this two IC's should be ROM and the first one is RAM, powered directly.

I have an HP33C guts and I had a look at their IC's an mainboard. The topmost IC is an 1LB901, and the remaining other (only one, button position) is an 1MA something (unreadable). As the HP34C has two 1MA IC's and one 1LB, I guess their position is:

1LB902

1MAxxxxx

1MAxxxxx

Would you try this configuration, Pyerre? Now that I see the codes you posted first, it seems to me the different prefixed IC (1LA) would go in the different position, as the other two share the same prefix (1MA; probably ROM).

Hope you have success. Let us know about it!

Cheers.


#11

Hi,

First, many thanks for all of helps (public & private emails).

Here's how make it works again :

Top : 1LB902 - 80402 - SGP02

Center : 1MA10015 - SGP8041215

Bottom : 1MA114 - 80382 - SGP14

Thanks,
Pyerre

#12

Pin 8 of the memory chips in the Spice series is the power supply pin.
The top location is wired sepearately back to the PSU module. On -E models, this connection is linked to the main power line in the PSU module, so all 3 locations are equivalent. On the -C models (includign the HP34C), the PSU module contains an extra couple of diodes and a resistor to provide a 'continuous' supply to the top IC location, to maintain the contents of the RAM.
If you get the ICs in the wrong places, then the machine should work, but you'll lose the contents of memory when you turn it off.
In all cases, pin 1 (notched end) of the IC points towards the display (this applies to the 40 pin CPU chip also).


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