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Fender HR Deluxe Channel switching problems

5/21/2000 8:10 AM
Paul Birch
Fender HR Deluxe Channel switching problems
Hi Folks!  
I am having a terrible time with this HR Deluxe... After the amp has been on for a couple of minutes and is played at club volume, the channels start freaking out. The amp will not stay in any particular just kinda buzzes and switches on its own. Thus making it a heavy, useless piece of stage gear. It does it with and without the footswitch plugged in. I did some research on my own using the schematics posted on Steve Ahola's site (Thanks a million Steve!!!)  
Here are the vitals as listed on the schematic...  
TP31(ref pin ch select) +1.052v  
Fender shows -1.37v  
TP32(input pin ch select) +.551v ch off +2.62 ch on  
Fender -.527v ch off -2.53v ch on  
TP33(output pin ch select)  
+16.9v nml -12.8 drive(yellow) -13.2v more(red)  
Fender -15v nml -13.5v drive -13.9v more  
TP34 (ref pin drive/more drive)  
-11.5v nml -5.14v drive(yellow) -4.8v more(red)  
Fender -13.3v nml -5.46v drive -4.36 more  
TP35 (input pin drive/more drive)(with footswitch)  
-3.37v drive(yellow) -6.57v more(red)  
Fender -3.33v drive -6.54v more  
TP36 (output pin drive/more drive)  
-15.1v nml -15.1 drive(yellow) +16.9v more(red)  
Fender -16v nml -16v drive -16v more  
If anyone could help me locate the problem I would be most appreciative. Thanks so much for your consideration.  
5/21/2000 1:23 PM
Randy Jamz

I don't have the schematic in front of me, but usually those damn plastic 1/4" jacks aren't worth anything. They seem to get a mind of their own, and they do the switching on these inbred Fenders. Change every jack that can't outrun you, and you should be better off. I can't recall what else I've done. If the jacks alone don't do it, let me know, and I'll go over my notes.
5/21/2000 6:07 PM

Common problem. In that line of fender amps the + or - 16 volts drops out alot causing all kind of switching problem. The 2 power resistors and zener doides that are used to drop the voltage get hot and with time and vibration the solder joints go intermitant causing the problem you have the voltage is used in the SS switching. This is almost always the problem
5/22/2000 1:32 AM
Paul Birch

That sounds like what I'm experiencing Gus. I'll go over those areas and check them out. Perhaps changing out and/or moving the power resistors away from the board might do the trick. Doing the same with the zenors as well? The puzzling thing is that my voltages are not what they are supposed to be @ tp31,32,and tp33. I'll check for a bad joint at the get go. I dont believe the footswitch is causing the problems because I've got the same thing happining when it isn't pluged in. I'll keep you al posted and thanks Guys!
5/24/2000 5:11 AM
Paul Birch

Hey folks,  
Just wanted to follow up on this HR Deluxe.  
I removed the 470 ohm power resistors from the circuit board and used some kwik-set JB weld to glue them to the metal chassis, and wired them back to their origional terminations. (I figured this way they would be able to dissipate all that heat) I then replaced the two 1/2 watt 16v zenor diodes with a set of 5 watters. I soldered them in about 3/16" off of the board for better heat dissipation. I figured that 5 watters wouldn't generate as much heat as the 1/2 watters did because they are only working at 1/10 of ther rated capacity.  
Channel switching is rock solid now!!! And I thank all of you who keep this bbs running...could not have done it without you.  
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