Re: PG506 Repair - I had a Great Day today/


Michael W. Lynch
 

On Sun, May 2, 2021 at 07:44 AM, tek_547 wrote:


If you have the possibility pls check the 5V1 at the collector from Q70, mine
is 4,75V. For TTL logic (U670, 671, 673 & 675) this is the absolute minimum.
Maybe this is the reason of the problem so I am interested in the value from
your PG506.

And also look that if inside your PG506 T130 in the power supply is about
70°C when the STD AMP switch is activated. So almost not possible to you put
your finger on the windings of it. Is this on yours the same?
Thanks so far and hopefully you have some suggestions, Rene
Rene,

I will take another look at mine tomorrow. I will give you as much as I can as far has how mine acts. I will pay special attention to T130, including some temperature measurements. Your U400 measurements that you are describing do not sound correct.

Glad you included your control settings as we always need to standardize our panel settings when making measurements and observations, so that we can be on the same page. I believe that you can check the opto-couplers using a diode test. I had one bad 4N27 on my unit, one side checked as an NPN and the other side checked open, it should have checked as a diode.

One thing that you may find helpful and what helped me diagnose the issue with mine was actually diagramming the inputs, outputs and cross connections on U400. It is an SN74LS00N Quad 2 input Positive NAND gate, so sorting out what goes in and what comes out is important and helpful. This is how I finally isolated and found my problems, since U400 is sort of the "doorkeeper" to the rest of the circuit. .

--
Michael Lynch
Dardanelle, AR

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