Blown part in Fender Blues Deluxe Reissue

[R.G.]

The low voltage supply for +/-15V in the Blues Deluxe and also the Hot Rod Deluxe is a disaster waiting to happen. It is extremely common for these amps to fail in either the zeners, the resistors feeding the zeners, the filter caps before/after the zeners, and/or the rectifiers feeding the whole mess.

Perhaps the most common failure is that the resistors feeding the zeners get so hot that they either melt the solder off their leads and unsolder themselves on the spot. This can happen because of an overheated and shorted zener, or any overload on the circuits they feed. This is probably also the worst failure, because the resistors can also char the PCB material under them so that the PCB is permanently damaged in that spot.

The best thing to do is to substitute a pair of three-terminal regulators for the resistor/zener combination. This permanently fixes the problems by converting it into a current- and thermally-limited regulated supply. This is, unfortunately, a job for the professional repair tech.

I can only guess that the Fender designer or, more likely, the MBA in charge of making money on that design, went with saving $0.20 on parts by going to a less-reliable design. The reasoning goes like this "if we put in the cheaper parts, we save the parts cost on every amp. Out of that money, we have to pay for the few amps that fail within the warranty period. If the number that fail in the warranty period is lower than the parts savings, then I get my next performance bonus. And I'll probably be moved to some other area before the amps start to faily in the field and give us a bad name ... kewl..."

[merlot]

Wow! If I'm calculating correctly, they pushed it to the limit with those resistors. At 48 volts and 470 ohms, that's a power rating of 4.9 watts--way too close for comfort on a 5w 10% resistor. I can see one mod I'll be doing very soon. I imagine it's that close with the zeners, too.

[jrfrond]

Wow! If I'm calculating correctly, they pushed it to the limit with those resistors.

Pushing to the limit is not exactly a new concept in guitar amps!

[newsong]

I have a '96 Blues Deluxe and boy have had problems with those 470ohm resistors. I've resoldered them twice and now the board is charred with no sound. I tossed the sandblock 470's and decided to try mounting some aluminum housed 500 ohm Dale resistors off the pcb and mounted to the steel chassis behind the board, wired in with 20 ga teflon silver wire, but did not replace the zeners.
When I fired it up there was a real bad hum, although I now have sound.
do you think if I replace the zeners, It will take care of this?

[melvin]

Sorry. I was using an original BD schematic.

I agree that this can be a tedious job for someone who is not familiar with how to squeeze the pot shafts past the chassis lip on new Fender amps.

Is there a better way than taking the tube pcb out to make room for the squeezing bit? I really hate that whole process... Ampeg had it right when they had a removable window on the other side...

[darrellcheng]

Yea, I've managed to squeeze the board out by unscrewing the control panel stuff, and then managing to flex the ribbon cables so that i can get the board out without undoing all the wires.

[Enzo]

The ribbons are not what hangs me up, I always have to clip some tie wraps to free the wires to the transformer.

[Gtr_tech]

Take some voltage readings and find out. If one/both of the 15v rails are off then you have other problems.

[michael peck]

my hot rod deville had same prob, 10 pin wire straps rattled loose next to solder, after about 5 yrs of use, i over heated board fixing it and amp works great now but has nasty hum, ok for loud gigs but not in rec studio

[newsong]

Just an update: I changed the Zeners, which I don't think were bad. What was causing the hum was an open in my #1 input jack. Once that was retouched, everything seems to work fine and those outboard dropping resistors should remedy the cold solderjoints on the board. Thanks for all the help.