Re: do have I have to change my guitar amp's zener diodes?


"Tim Schwartz" <timhhk@xxxxxxxxxxx> wrote in message
news:TQtXf.491$v9.61@xxxxxxxxxxx
thefender@xxxxxxxxxxxxx wrote:
HI all,

I've no experience in repairing or in electronics but I opened my amp
to change an input jack and noticed this:

http://img360.imageshack.us/img360/8841/scanimage0012tf.png

http://img451.imageshack.us/img451/6885/scanimage0047pi.png

http://img84.imageshack.us/img84/7444/scanimage0024my.png

It looks like zener diodes have burned the board under them.

The amp works great, the sound is ok, should I change them?

here is some schematics I found:
http://img84.imageshack.us/img84/4839/schemaparz6bm.png

here's the zeners' pdf:
http://www.ortodoxism.ro/datasheets/eic/1N5368A.pdf

thanks for your help

PS: sorry for my english...

Hello,

First, don't panic. I'd measure the voltage(s) and see if it(they)
is(are) correct. They are certainly running warm, as they have baked the
board a bit, and they are near some high wattage resistors. If the
voltage is correct, you could leave them alone.

If you want to replace them as a precaution, I'd solder the new one is
spaced up off the board a bit so that they get more cooling air around
them, maybe .25 in or so. Be very careful, as when they bake the board
like this the solder foils can get fragile.

Regards,
Tim Schwartz
Bristol Electronics


All agreed with Tim. What you have there is what typically happens when this
simple power resistor / 5 watt zener arrangement is used to derive the + / -
15v ( or whatever ) supplies for the front end opamps, from the + / - 50v
( or whatever ) rails for the power amp. I see it all the time.

If you really want to do something about it, just check the state of the
joints on the other side of the board. You will probably find that they are
quite crystalline, so may benefit from being reflowed with some new solder,
before they start to go intermittent ( which of course, they will, at the
most inopportune time, right in the middle of a gig !! ). But as Tim says,
be a liitle careful of the track foils, as they will probably no longer be
bonded to the board very well.

Arfa


.

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