Blues jr low voltage problem

[pontiacpete]

I tried reversing the cap and I get -25v. What the hell? I’m going to test the Zener today. Also tried reversing the cap and the Zener and there was no voltage

can anyone explain the difference between rev A and rev C. I just don’t understand how this can be

[Helmholtz]

Reversing the zener results in a short.

Connecting an ecap with wrong polarity will damage the cap.
If not clear if the ecap is inserted correctly, use your DCV meter to determine actual voltage polarity at the cap terminals.

[pontiacpete]

Helmholtz what do you think about the differences in these schematics?

[Helmholtz]

Not familiar with the different revisions.

In this schematic: file:///C:/Users/User/Downloads/Fender_blues_junior_rev_a-2.pdf
the polarity of C34 is wrong. Positive must go to ground.
Zener polarity is shown correctly: D7 anode to ground and D8 cathode to ground. You can check using your Ohmmeter.

[pontiacpete]

Wire 1k in series with the zener and connect to a DCV of maybe 20V.
Measure the voltage across the zener. In one direction you should get 0.7V and in the other the zener voltage.

Most likely you got an 8.2V zener (1N4738A).
Any numbers on the glass body?

So this is strange I measure -15v one and the other way +15v

[pontiacpete]

So finally i see +-15v. The latest issue was a broken solder joint at the cathode of the Zener. No big surprise being that i took in and out numerous times.
the real cure here was reversing the cap C34.

thanks to all of you who helped me! Have a Happy New Year

[Jon Snell]

Pleased you found the 'fault'.
Happy New Year to you and all.

[g1]

In case you were unaware, reverse polarity damages the cap so C34 should be replaced with a new one (and board marking should be corrected).