HP 3325B A26 Assembly: low byte SRAM, and an incorrect signature

A quick comment on the 3325B service manual – Thanks to a kind contributor.

3325b kernel sa test u27 pin10

The kernel SA test is a bit flaky on A26U27 PIN 10. This is an inverter output, and can’t be same as the input… correct signature is A70F. Appears to be a misprint in the HP service manual!

3325b a26u27 74as04

In the present case – the culprit was one of the SRAMs, the lower byte. Fortunately, not really a rare part, and easily sourced and replaced, once you know that this is the circuit at fault. You might want to check this very carefully, because there are multiple versions of the 3325A/3325B control boards.

3325b srams

One thought on “HP 3325B A26 Assembly: low byte SRAM, and an incorrect signature”

  1. The HP manuals are far from perfect – I found several SA documentation errors in the 3325A main CPU board (A6) section (mostly TTL logic) which led me to replace a couple of IC’s needlessly.

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