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Found these inside a non-working 71B
03-14-2018, 05:17 PM
Post: #87
RE: Found these inside a non-working 71B
(03-14-2018 04:20 PM)Paul Berger (Canada) Wrote:  I will have to try that 64K mod I have a 128K module in pieces right now because the SRAM was bad on one of the boards, that is fixed now, at least I ran diags for about 18 hours and it did not find a problem. I was not so lucky my bad SRAM was was on the base board in the middle of the stack and had more than one bad chip, it is now a single 32K SRAM. I should look and see if the later modules that used a single 32K SRAM instead of 4 8K have a similar arrangement, if not I can always lift the pin and ground it.

Is that your document? I can fill in more of the pinout of the 1L?4 chip if you wish.
Yes, this document is mine.
Of course I will be interested with the identification of more pins. Especially pins that may define the ROM/RAM type, capacity and organisation (1 x 32K, 4 x 8K, ...).
The pin defining the last-chip-in-chain was easy to find since it is connected to a pad.

Actually, the pictures were taken when I fixed a bad SRAM too !
Does it mean RAM failures in HHP modules are common ? I may suspect a excessive supply voltage, the HP71 power supply may go up to 6.5V, and standard chips have a max operating voltage of 5.5V and sometimes an AMR of 6V !
I didn't see any special circuitry to reduce the supply voltage in the HHP or CMT modules. A simple diode may help.

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Messages In This Thread
RE: Found these inside a non-working 71B - J-F Garnier - 03-14-2018 05:17 PM
What's U10? - Dave Frederickson - 03-15-2018, 03:43 PM

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