2004 Fender HRDlx Volume Loss

[Kryger]

Hi, new member here- was referred here by a couple people from the strat-talk forums.

My problem is this:
I purchased an HRDlx about a month and a half ago off of craigslist. When I played the amp at the man's house, it worked great. It worked at my house for it's first 30 minute session. My second session, however, the clean channel had a HUGE volume loss. I could turn it all the way up to 12 and drums would still drown me out easily. The dirty channel worked fine, except for a couple times there would be absolutely no volume coming from this channel- just static (however, it has worked fine since).

I could care less about the dirty channel, as I never intended on using it.

Summary:
Huge volume loss on clean channel, recently a "buzz" has developed. Hard to be sure, but I feel like the tone of this amp is getting worse.

What I have tried:
Changed all the tubes out - no change.
Used multimeter testing a couple test points- all have read close or spot on to readings provided on schematic.
Plugged guitar into "Power Amp In" input- guitar signal plays through amp normally.

Other possibly helpful info:
The bottom of two of the caps bulge out very slightly, not sure if it is glue or corrosion.
Fuse looks good.


Thanks!

[52 Bill]

Welcome to the place. The first thing that I test on any of these amps is the low voltage power supplies. Make certain that the + and - 16 volts are working and that the two large 5 watt resistors are solidly connected, etc.

As the problem is mainly with the clean channel my first thought would be a problem with the relay contacts. I don't see a lot of relay problems with these amps, but I have replaced a few. If you look at the pc board, there are two small rectangular boxes. These are the relays that switch the signal between the clean and dirty channels. Inside each relay is the equivalent of a double pole double throw switch, just like a stomp box switch. The contacts can become dirty and oxidized and can cause the problems that you are describing.

As a first test, rapidly switch the channels back and forth and see if the clean signal will come back intermittently. Another quick test would be to lightly tap on the relay cases with the handle of a screwdriver. The better test would be to read the resistance of the normally closed contacts with an ohm meter to see if they are in fact connecting as they should. Fortunately the clean channel contacts are the ones that are normally closed, so you can test them without powering the amp on.

Go to the Fender support site and get a copy of the schematic for your amp. On it you will see what circuits are supposed to be connected together by the relay contacts. This way you can test the resistance of the contacts without having to remove the board.

Hope that this helps.

[Kryger]

Welcome to the place. The first thing that I test on any of these amps is the low voltage power supplies. Make certain that the + and - 16 volts are working and that the two large 5 watt resistors are solidly connected, etc.

As the problem is mainly with the clean channel my first thought would be a problem with the relay contacts. I don't see a lot of relay problems with these amps, but I have replaced a few. If you look at the pc board, there are two small rectangular boxes. These are the relays that switch the signal between the clean and dirty channels. Inside each relay is the equivalent of a double pole double throw switch, just like a stomp box switch. The contacts can become dirty and oxidized and can cause the problems that you are describing.

As a first test, rapidly switch the channels back and forth and see if the clean signal will come back intermittently. Another quick test would be to lightly tap on the relay cases with the handle of a screwdriver. The better test would be to read the resistance of the normally closed contacts with an ohm meter to see if they are in fact connecting as they should. Fortunately the clean channel contacts are the ones that are normally closed, so you can test them without powering the amp on.

Go to the Fender support site and get a copy of the schematic for your amp. On it you will see what circuits are supposed to be connected together by the relay contacts. This way you can test the resistance of the contacts without having to remove the board.

Hope that this helps.

Thank you very much! I have not tried this and will attempt it tonight. Its very refreshing to get new advice other than, "Change your tubes" haha.

Best,
Kryger