Low distorted output, no channel switching on Blues Deluxe

[5thumbs]

Hi,
This amp is not playing properly and the drive light LED doesn't light up.

Things I’ve done from reading other threads on this forum:
1. I have replaced the 330 ohm 5 watt resisters (R85, R86) with 500 ohm 5 watt resisters.
2. I have replaced the 2 IN5353B diodes (CR22, CR23).
3. I have replaced the 10k resister (R71) with a 100k resister
4. Replaced RY1 and RY2 with new relays.

Readings:
@CP16 = -.11
@CP17 = 41.21 VAC
@C38 = .013VDC
@C39 = .000
@CR22 = .012VDC
@ CR23 = .008VDC

[Jazz P Bass]

The repairs that you did where to fix something else or was it for preventive maintenance?
Or where you trying to fix the posted issue. "This amp is not playing properly and the drive light LED doesn't light up."
Ah. It is a Fender Blues Deluxe.
Attached is a readable schematic.

[5thumbs]

Hi Jazz P,
I am trying to get the channel switching circuit to work. It seems to have erratic readings. I think what is happening is the normal and drive channels are both playing and canceling out signal, but I hope someone can educate me!

Tim

[52 Bill]

The two signals can't cancel each other out. The switching changes the gain levels of the preamp, there aren't two separate signal paths.

I can't understand your voltage readings. What DC voltage do you get at each side of the new 500 ohm 5 watt resistors (R85 and R86)? There should be approximately plus and minus 45 and 16 at each end.

[5thumbs]

Hi 52 Bill,
I get -54.46 on both sides of the R86 resistor. I get .02 on both sides of the R85 resistor.

[52 Bill]

Well then there's a good place to start repairs.

Check the positive voltage at the positive end of diode CR20. Is there 50 volts there? If yes, check the pc traces around R85. If no voltage, then check diode CR20 and cap C38.

Check the voltage at both ends of Zener diode CR23. If there is no voltage there, check the traces from R86 to the diode.

You need both 16 volt supplies to be working before you can move forward with the repairs.

[5thumbs]

I get 54 volts on one leg of the transformer winding and 0 on the other. Is that correct? or should one side be +54 and the other -54?

[52 Bill]

If you are reading the AC voltage directly from the transformer then there will be no DC voltage there at all. There will be 50 volts AC on the ungrounded side of the winding and there will be 0 volts on the grounded side of the winding, this of course is measured referenced to ground.

If you are reading the DC voltages coming from the rectifiers there should be both plus and minus 50 volts DC at each of the two filter caps.

[pecorporation]

Reflow foot switch jack & all tube sockets.