HP85A Power Issues

[Paul Dale]

I'm looking at an HP85A which has some unknown "power issues".
Can anyone enlighten me on what these might typically involve?

I'm up to soldering and replacing passive components. But finding replacement ICs will be tricky.


- Pauli

[Paul Berger (Canada)]

That is a very broad question, "power issues" could range from something simple like a blown fuse or the incorrect AC voltage selected, to some obscure component failure that is pulling down one of the voltages. Has the seller tried to plug it in and turn it on? Any description of the behaviour when that is attempted? The good news is there are schematics available for the 85A and 85B, but you would need at least a meter to trouble shoot a power issue. If you are up to the challenge, we can help.

Paul.

[cruff]

(03-08-2017 09:02 AM)Paul Dale Wrote:  I'm looking at an HP85A which has some unknown "power issues".

Can you provide details of the problem? Lack of +5V, etc?

[Paul Dale]

I don't know the issues, if any, yet.

I'll try to find out more.

I've got a meter, no CRO though.


Pauli

[cruff]

If power supply board fuse F1 blows (located between the collector of Q2 and R3), possibly due to either a short or being powered on with no connection of the ribbon cables to the logic board, it results in bad voltages.