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NivagSwedna · 02-17-2023, 05:33 PM

I bought a non-working HP11C and I am trying to gradually work through its problems. It seems to have some strange damage to its traces anyway...

Whilst repairing it I noticed that two of the PCB traces were shorted which seems wrong since HP made the effort to route them across the PCB... anyway they track back to a small blue component, which appears to currently be low resistance.

The small blue component is marked 181J (see attached)

I would expect this to not be low resistance? Is this a 180pF capacitor (maybe Mica)?

Thanks in advance

teenix · (This post was last modified: 02-18-2023 05:16 AM by teenix.)

180pF sounds right, J is +/- 5%

cheers

Tony

NivagSwedna · 02-18-2023, 05:06 PM

On reflection I realised that this was unlikely to be my problem! The processor oscillator comprises this small capacitor and the neighbouring inductor.

I was measuring low resistance due to the parallel inductor.

Traced my real problem to a destroyed trace all the way across the PCB under the processor!

Repaired two oscillator traces with bodge wires and repaired a few traces near the battery compartment on both sides of the board... and hey presto! It's repaired!