Hot Rod deluxe signal when clean volume off

[Granth]

I've got a Hot Rod Deluxe that has recently started playing up. When the clean channel is all the way off, the guitar can still be heard, albeit at low volume, and is fairly distorted. On the drive/distortion channels all seems well and turning the master down on those channels does not lead to any output.

Any suggestions would be great

Cheers

Grant

[Amp Kat]

I would go down the test point guide and check all the test points in this schematic. Footswitch jack could be problem but check the voltage to energize the solonoids on the relays and the switching transistors is it Q4 maybe ?

http://www.blueguitar.org/new/schem/...rod_deluxe.pdf

[Granth]

screwy numbers

Thanks for your reply, I've got some really strnge numbers (to a lay person anyway!)
Test points: Amp on 'clean' channel
1 0mV
2 235V
3 1.75V
4 0
5 228V
6 1.84V
7 0
8 232V
9 1.784V
10 0.9mV(?)
11 0.232V
12 1.822V
13 0
14 0
15 3.3mV
16 0
17 -1.2mV
18 -0.9mV
19 0
20 4mV
21 0
22 -1.5mV
23 to 30 not accessible (too tired to pull out that particular board at this hour!)
31 1.363V
32 0.513V
33 16.63V
34 -12.3V
35 -0.5V
36 -15.5V

So looks like the footswitch jack is pretty much ok. I'll admit to being lost at this point.

Thanks for your help!

Cheers

Grant

[Amp Kat]

Look to the bottom left corner of the schematic and it says footswitch operation which are TP 31 to 36. These are the ones you want to perform and notice it says to the right with footswitch on and with footswitch off. Give us a on/off reading of those.

[Granth]

on/off readings

Thaks for you continued help on this topic by the way!

here are the test point results (no footswitch)
clean drive more drive
31 1.363 1.069 1.069
32 0.513 9.70 9.70
33 16.63 -13.48 -13.9
34 -12.3 -5.1 -4.76
35 -0.5 -0.51 -9.69
36 -15.5 -15.6 16.33

I have gone to the missed test points as well

23 0
24 263
25 244
26 35.2
27 430
28 430

Hope it helps

Cheers

Grant

[Amp Kat]

Hmm all of those voltages checked pretty good and actually spot on to be quite honest. At this point you almost need a scope to watch the signal and see where it's not stopping at. IME bleeding over is usually caused by a transistor problem and the only ones I see that would cause that are J1 and J2 so you may try those test points maybe 16,17,18. Another thing which it could also be is a faulty volume pot so you might want to ohm out that pot and make sure it is going up to full range attenuation. I really doubt a relay is bad as they rarely do go bad but I guess it's possible that one is hanging up or the solonoid isn't working pulling the contacts in & out. May be an Enzo one as he's much better than I at this type so maybe he'll chime in with more expertise.

[Ronsonic]

Forest and Trees time. Don't get too buried in the pine needles.

Most often a control that doesn't go to zero is the result of a poor ground. The HRDs, especially the early one with the input jacks that look like the FX jacks have known problems with both poor solders and an ill-designed ground buss on the preamp section. There's even a bulletin on this.

Before getting in deep, drop the board and reflow all those crappy joints you see in the preamp / control section. Especially the jacks,the pots and the mounting bracket wings on those pots. Those brackets are part of the ground buss and being both large and on the edge of the board the wave soldering did a poor job on them. In fact, you should reflow everything larger than a 1/2W resistor on that board. Just do it. It is faster than trying to figure out which joint is bad or going through a bunch of diagnostics to get there. Even if the problem turns out to be something else, this is necessary and valid.

[Granth]

Thanks for the info, I'll get onto the board asap. It is a bit wierd (the signal that I'm getting with the pots all down) almost like I'm picking up a very low signal from the 'drive' stage, it's not a clean signal at all. Althought this is odd because when I activate the drive stage there is no output at all with the master all the way down.

If you could clear up a question for a newbie as well, why do the readings at some of the test points come out so high compared with those indicated on the diagrams? Probably a fairly elementary answer but I've got to learn somehow!

thanks again for everyone's help.

Cheers
Grant

[Amp Kat]

Thanks for the info, I'll get onto the board asap. It is a bit wierd (the signal that I'm getting with the pots all down) almost like I'm picking up a very low signal from the 'drive' stage, it's not a clean signal at all. Althought this is odd because when I activate the drive stage there is no output at all with the master all the way down.

If you could clear up a question for a newbie as well, why do the readings at some of the test points come out so high compared with those indicated on the diagrams? Probably a fairly elementary answer but I've got to learn somehow!

thanks again for everyone's help.

Cheers
Grant

Those are AC readings Grant and if you read below it will say use a true RMS meter for them. You are probably reading them as VDC. I do agree with Ronsonic on poor solder joints and that is always a reason for concern with these type amps as you will see when you turn it over. Let us know how it turns out. I think the distortion you are hearing is the drive channel bleeding through to the clean channel. Try turning the gain pot on the drive channel and see if the gain changes or if it's just a steady gain no matter what.

[Mars Amp Repair]

hello
this sounds like classic decoupling filter cap being leaky or open. You won't ususally hear any hum as the cap (ususally a 22uf @ 450V) isn't really needed for power supply filtering at the preamp stages.
Instead, it's there to keep the signal from one high gain stage from sneaking through the b+ line to the next stage.

My money's on the very last filter cap in the preamp line. You can just jump it with a known good one before you pull the board out...glen

[Granth]

thanks again to everyone for the tips, I've been hunting for the cap mentioned above but having trouble identifying it, can anyone point it out for me as there doesn't seem to be a 22uf on the schematic, only 0.022uf 400V that looks like it is acting in the manner described above

cheers

grant

[Dave Curtis, dB AudioTech]

C36

[Granth]

thanks for that!

[Dave Curtis, dB AudioTech]

But I don't think that's it, since that node (X) feeds both the clean and the distortion tubes... It would be a consideration if those sections were fed by different nodes of the power supply. You could try jumping a 20uf cap across C36 as Glen said, but I think you'll have the same symptom.

[rf7]

If you're just putting a good cap across a leaky cap, won't the leaky cap still be leaking signal into the circuit?