Re: New member with early HP computers

Paul Berger

On 2019-08-25 1:50 p.m., silverray.russia@... wrote:

I'm newby in your group.
First of all excuse me for my English, I'm from Russia and have no practice. Therefore my posts may contain some mistakes so I'm sorry.

 I like vintage computers especially from HP. I have two early models -- HP 9825B and HP 85.
 Unfortunately my 9825 isn't work correctly -- I repaired the power supply module but the computer didn't resurrect :(
 I checked up all voltages and they are OK. If I disconnect KDP interface cable and make power on -- LEDs are light on and the beeper is sound on.
 I checked up the clock frequency -- all OK, approx. 6MHz.

 Could you help me with searching of solvetion?

Best Regards,

Does the PVAL signal from the power supply go high?  If it remains low the processor will be held reset.

What was the fault on the power supply?  Some failure modes can result in higher than normal voltages going to components in the system, for instance I had one that to +5V pass transistor failed short putting about +25V on the +5 line.

Do you have any instruments like an oscilloscope or a logic analyzer you can use to troubleshoot?  If all you have is a meter troubleshooting may be difficult.

I would second what Craig said, I would clean the edge connectors and reseat them a couple time to make sure they are ok.  I had one that would not start up until I cleaned the edge connector even though there was no visible contamination. 


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