Hot Rod Deluxe Channel problem

[hlk]

Hello!

I am having a little problem here with my HRDx.
It is working fine on the clean channel, but when I try to play it with the Drive channel,
The LED is showing as if the channel was switched (drive/more drive), but it doesn't
output any sound at all.

I tried it with and without the footswitch connected, and it's the same.

Any help would be appreciated!!

Thanks
wK

[52 Bill]

Well there can be a problem with the relays or with the master volume control. Get a copy of the schematic for your amp and we can help guide you through the process.

Try this, listen to the background noise of the amp and turn up and down the master volume control. Do you hear a change in the sound?

[hlk]

hey there,
thanks for the quick reply.
I have downloaded the schematic from the fender site.

As for the background noise on the drive channel -
there seems to be a 'natural' hum that goes up and down together with me playing
with the master knob - this probably means the pot is ok?

thanks again!
wk

[52 Bill]

Yes that is a good sign that the master changes the hum.

The first thing you need to check is tube V2. The best way is to substitute it with a new one or one from another amp. You could try switching the first 2 preamp tubes to see what happens.

After that, it will require you to get into the guts of the amp. What sort of skills do you have and what sorts of testing equipment do you have available?

[hlk]

unfortunately I don't have a substitute tube
I will try replacing the first two. the light shines on all of the tubes though i dunno what it means.

as for electronics skills - i believe i can replace a component without causing any harm. i have a voltmeter and a solderer.

thanks!

[hlk]

ok, i switched v1 with v2 and the problem remains the same ...
seems like i have to start draining them caps

[hlk]

hey again,

i hate being rude but i am still stuck with this problem as i don't know what to do or check.... can u please guide me on what to do?

thanks again

[52 Bill]

Didn't know you were waiting for advice. When you swapped the two tubes, the distortion channel still didn't work, but did the clean channel still work?

Before we get too deep into this, how old is this amp? Are you the original owner? Fender has a very good 5 year warranty that covers these types of things.

The next tests will require you to work with the amp plugged in and turned on. If this is beyond your pay grade, then find some one to help you, or take the amp in for service.

There have been a lot of problems with the low voltage power supply in these amps, check to be sure that the two large 470 ohm, rectangular power resistors (R78 and R79) are soldered securely and that there is a steady plus and minus 16vdc available from the power supply.

You need to isolate the problem until you find out which circuit is causing the signal to stop. If the clean channel is working normally, then you know that preamp stages 1-3 are working ok. The only part of the preamp that is only used for the distortion channel starts at the relay K2-B and ends at the second half of the same relay K2-A.

When the distortion channel is selected, the preamp signal is fed through K2-B to the input of tube V2B. The output of V2B is sent through the master volume and then is sent to relay K2-A and on to the power amp. You say that you can hear the master volume control reduce the hum level as it is rotated, so it would appear that the master control is ok.

Using your voltmeter lead, touch it to test point TP10. Do you hear a hum? Turn up the master if it has been turned down. If you do hear a hum, then the problem is before the tube. If you don't hear a hum then the tube or one of the related components before the master is the problem.

[hlk]

Dear Mr Bill,

- Yes, after swapping the tubes, the clean worked and distortion didn't.
- Unfortunately, the 5 year warranty has already expired.
- I checked voltage on the R78, R79 resistors, and both showed 32v
- I touched TP10 and there was indeed an 'extra' hum.

(Just out of curiosity, I checked the voltage on R19, R20, R42 and all showed 0,
but when I checked R21 it showed 32v (if i recall correctly))

Where could the problem be?

Thanks for your time,
wk

[doctor]

Dear Mr Bill,

- Yes, after swapping the tubes, the clean worked and distortion didn't.
- Unfortunately, the 5 year warranty has already expired.
- I checked voltage on the R78, R79 resistors, and both showed 32v
- I touched TP10 and there was indeed an 'extra' hum.

(Just out of curiosity, I checked the voltage on R19, R20, R42 and all showed 0,
but when I checked R21 it showed 32v (if i recall correctly))

Where could the problem be?

Thanks for your time,
wk

Once I had a similar problem.

Hot Rod Deluxe schematic has the voltages map named “Footswitch Operation” that must be checked. If at least one measured voltage isn’t correct, try firstly to replace dual opamp U3 (4560, 4565 and 4580 are suitable).

Good luck.

[52 Bill]

- I checked voltage on the R78, R79 resistors, and both showed 32v

One side of each resistor should show + or - 48vdc and the other end should read + or - 16vdc. It's the 16 volt side that you need be sure works correctly.

(Just out of curiosity, I checked the voltage on R19, R20, R42 and all showed 0, but when I checked R21 it showed 32v (if i recall correctly))

R19, R20 and R42 are signal path resistors, so there should not be any dc voltage there. R21 is the cathode resistor for V2-B, there should be about 2 volts there.

If you heard hum when you touched TP10, then you know that the signal will pass through tube V2-B. So it would seem that the problem is either in relay K2 or capacitor C3.

With the amp in the distortion mode, carefully read the voltages on both sides of C2. There should be maybe 200vdc on one side and 0 volts on the other side. When you touch your probe to the caps leads, listen for hum or noise from the amp. Again the master should be turned up during this test.

If you do not hear any hum, the relay K2 is suspect, if you do hear hum then you will need to check to see if cap C3 is shorted.

[hlk]

Hello Bill,

- Regarding the +/- 16v : you are right, I did something wrong while checking them.
I re-checked it and they are both good.

- Since I haven't disassembled the amp yet, I checked voltages of C2 by measuring
them on the respective legs of R16 and R18, and one of them showed 0,
and the other about 200v like you said. Is that ok?

- while probing the upper lower leg of R16 I heard a hum (and even an explosion like sound), which went up and down together with the Master volume.

This leads to the conclusion that the problem is with C3,
and since I don't have access to its leads from the front of the board,
is there a way to check if it is shorted without opening the entire amp?

Thanks
wK

[52 Bill]

Just like C2, each end of C3 connects to a resistor, one end to R8 and the other to R27. Can you find those leads? All you need to see is if C3 is shorted. Turn off the amp and measure its resistance.

[hlk]

I turned off the amp and checked resistance on C3 and the meter showed some value.

[52 Bill]

What was the value?