Mark Bass Little Mark III Blowing Fuse

[x-pro]

Not enough measurements. There are 4 diodes in the bridge, not 2

[x-pro]

Assuming the diode bridge is OK, if we unsolder at least T22 and apply 25V again, what will be the voltage at bridge pins 1-2 ?

[misterc57]

I removed T22 T23, now seeing about 50% VDC at the plus and minus pins of BR1 of the VAC.

Example 20 VAC at BR1 AC and 10 VDC (plus and minus) BR1 DC outputs.

[misterc57]

But I am not convinced that T22 T23 are bad.

What is the recommended bench test for these?

Thank you

[misterc57]

R78 reads about 650K in circuit.

[x-pro]

Example 20 VAC at BR1 AC and 10 VDC (plus and minus) BR1 DC outputs.

That's without C39, C40 ?

[x-pro]

What is the recommended bench test for these?

Thank you

Why would you do that? If they are defective, just replace them.

R78 - Should be 270k

[misterc57]

That's without C39, C40 ?

C39 C40 are still installed

[x-pro]

Did you unsolder C39, C40? Did you check it?

[x-pro]

Example 20 VAC at BR1 AC and 10 VDC (plus and minus) BR1 DC outputs.

If there is a jumper in the CN9 connector, when 20V AC voltage with 60Hz frequency is applied to the bridge input, the bridge output (plus C39-minus C40) should be 2 times the voltage.

[misterc57]

Did you unsolder C39, C40? Did you check it?

Still soldered. Tested ok in circuit.

[misterc57]

If there is a jumper in the CN9 connector, when 20V AC voltage with 60Hz frequency is applied to the bridge input, the bridge output (plus C39-minus C40) should be 2 times the voltage.

CN9 is jumped. Are you saying I should be seeing double DC of AC, example 20 VAC becomes 40 VDC?

[x-pro]

yes

[misterc57]

I should have mentioned that after removing T22 T23 there is no more excess current draw.

[misterc57]

Assuming the diode bridge is OK, if we unsolder at least T22 and apply 25V again, what will be the voltage at bridge pins 1-2 ?

My bad. I was not paying attention to the BR1 pins.

So with 60 VAC coming into BR1 I see about 166 VDC at pins 1 and 2. Meter set to DC, red probe on pin 1, black probe on pin 2.

No excess current draw.