Hot rod deluxe RevA channel switching

[Oldmactech]

Rev A hot rod deluxe with New caps, Fromel upgrade having channel switching issues.
Symptoms:

On switch turns on yellow drive light in standby mode.
Clean channel functions well. Volume, reverb, tone. Master volume, drive non-functional. Yellow drive light lit.
Drive channel push button non-functional but causes a tiny flicker when depressed.

5w resistors 17.3, -17.13. Zeners the same.
Went over all solder, nothing seems bad.

Previously after the cap swap the yellow Drive light would be on for the first 30 seconds or so then go out and both channels would function as supposed to so I left it alone for a later day. Now it’s a later day.

thanks

[SoulFetish]

Well, in that case lets have a look at the schematic.

[Jon Snell]

Was the fault there before you replace the components?

[Oldmactech]

No, it had oozing capacitors and sounded horrible.

[Oldmactech]

I’m sorry, I don’t know how to post a schematic.

[Enzo]

There are specific test points with voltages on the schematic in the switching circuits, go through those.

[Jon Snell]

Schematic. Check, as Enzo suggests, the known and stated voltage points. Otherwise known as Test Points.

[mozz]

Those higher wattage resistors are known to cause problems on the positive and negative rails. Don't just look , resolder them and check the traces for cracks. I relocate them and run wires.

[Oldmactech]

Thanks. I suspect the resistors also- R78 and R79 those were replaced and I created a standoff to dissipate heat. The traces were damaged but rebuilt in the process. Yesterday when I was trouble shooting I pushed on one of them (R79) and the drive light blinked. I resoldered both but no change-good continuity. Likely is the problem but can quite isolate.

[Pedro Vecino]

The led is also part of the switching circuit.

[Oldmactech]

Thanks, yes. I think I will desolder the LED so I can take a look at it better. I’m baffled by it coming on yelllow even in standby. Maybe the switch needs looked at also? When I depress the drive switch I can see a tiny change in the LED, but never goes out as it should or goes red with “more drive.”

[Enzo]

It won't be a bad LED if it lights up.

Yellow is actually red and green on at once in that dual LED. To make red, they simply turn the geen side off.

PLEESE start with those test point voltages. They tell you what is happening in the circuit. The test point notes are all right nearby there.

[Oldmactech]

I’m back with some TP results. All taken per instruction (reverb off, drive Channel on etc) Skipping normal readings. FYI, I don’t possess a self ranging DVM so sone of these may be odd.

Tp Read Normal Component #

2 o 1.73 R4 pops when touched with probe.
4 -002 13mv R5
7 0 33mv R8 reading wanders but settles on 0
10 0 500mv R20
11 223 13.3 R22
13 -1.0 1.20 R28
14 -1.2 66mv R29
15 3.4 66mv R48
19 0 Switch U2 pin 3
20 0 switch U2 pin 1
22 0 Switch U2 pin 7
31 .72
32 9.9
33 2.05
34 -12.33 U3 switch pin 3
35 -.54 U3 switch pin 2
36 -16.14 U3 switch pin 1

U2 looks problematic..

thanks for any assistance.

[Enzo]

U2 is the reverb, shouldn't affect channel switching.

Note the test points 31 through 36 have multiple voltages. In other words the voltage changes depending on whether the button is pushed. So you need to tell us what voltages are present under each condition listed. And just for those test points.

[Oldmactech]

31-36 readings
First reading switch in, second out

31 .72 1.11
32 9.9 5.01
33 2.05 4.93
34 -12.33 -12.17
35 -.54 -5.01
36 -16.14 - 15.92

thanks.