Fender HR Deville Issue

[mikeboone]

I am looking at this amp fpr a friend. Initially, when powered up it would make a horrible noise (and very loud) when a cable was inserted in input 1, and a lesser noise but some guitar signal making it through to the output when inserted in input 2.

I started looking at the schem. to see where I could start. When I went back to it this morning, it made a different (pretty loud) buzz. I powered it down and started removing the preamp tubes to see where the buzz would stop. No luck.

When I removed the power tubes the buzz was still there but at a much lower volume level.

The amp has a few other problems to note. 1) I tried inserting a signal into the "power amp in" jack and got no sound at all. 2) The Drive Switch does not have any affect, it is stuck in the "drive" mode.

If there are any new style Fender heroes out there, please throw me a bone.

Thanks,

Mike

[daz]

If no sound with a guitar in the power amp/return jack as you said, i'd check the tube board. These deluxe/deville amps have a tendency to almost always have the solder joints of the tube sockets go bad eventually. Re-flow any suspicious ones and theres a good chance thats it. In fact, with most fender amps theres a huge issue with solder joints going south. True of many amps today, but fenders seem to be the worse.

[52 Bill]

As Daz noted, there are a few problem areas on these amps, including the solder joints on the power tube sockets. But from your description of the problem, the first place I'd check is the low voltage power supply.

There have probably been a hundred posts here about this so here it is in brief. There are two large power resistors in the low voltage power supply that either come unsoldered or otherwise fail due to overheating. Look for R78 and R79, they are 330 ohms @ 5 watts. Check the voltages on both sides of these resisitors, there should be about 35 volts on one side and 16 volts on the other side. One will have positive voltages and the other will have negative voltages. Also check the two zener diodes CR13 and CR14.

If either of the 16 volts supplies is missing, the amp will not channel switch, the reverb will not work, and due to a op amp buffer on the power amp in jack, no signal will pass through the power amp input.

[mikeboone]

OK... I did unearth a few issues but there is still an underlying problem.

1. The filter caps on the low voltage supply had a fractured solder joint.

2. The power amp in, and both input jacks had fractured solder joints as well.

I re-flowed all those joint and now all work normally and the channel switching is working. A guitar can be played though it to a certain volume, then the hum/buzz is too much. So, the majority of the aformentioned issues are corrected.

The big one... There is an unusually loud hum/buzz that is present at all times. The volume and tone stack have affect on it.

As stated earlier the noise is still there even with all tubes removed just at a lower volume. I have systematically re-flowed every single solder joint on the tube board to no avail.

I checked the bias voltage and it is close to the reference voltage on the schem. -58.3v

The power supply voltages are as follows:
B+ - 366 should be 471
Z - 376 should be 468
Y - 359 should be 413
X - 183 should be 364

With the tubes out (no load) - 476 across the board.

They are all low. Do the symptoms point towards failed power supply caps?

Any thoughts???

Oh and by the way... I own a HR Deluxe that I plan to sell very soon. BEFORE IT BREAKS!!!

[Enzo]

You measured the bias voltage, but did you measure the current through the tubes?

I don't see where you say you tried a DIFFERENT set of power tubes, did you?

Set your meter to AC volts and remeasure those B+ nodes. You are now measuring ripple on them. A few volts on the first node is normal, the screen node should have very little, adn the rest are more decouplers than filters and should be clean. Or scope the thing to see if your ripple is 60Hz or 120Hz.

CR14-17 are the B+ rectifiers wired in a bridge. are any of them open? Obviously do this with power off, but also make sure to open the standby switch so the PT winding doesn't interfere.

[mikeboone]

Thanks... Yes I did indeed try a known good tube compliment from my HR Deluxe.

I did not measure current, it was late and I didn't want to bust out the bias rig. I checked as reference only to see if it was way out of spec.

I did check all the rectifier and they are OK. I will check again ensuring the standby switch is open.

I will put the scope on it tonight and look for ripple. I hadn't thought of that.

Thanks again..
Mike

[mikeboone]

Thanks guys...

Enzo, I found that C34&35 had 101 VAC on the B+ node. Problem resolved.