Fender SS amp - heatsink failed - now blowing fuses - I've got details.....

[J M Fahey]

In those stinking (literally) amps I start by blowing a lot of compressed air to get rid of the bulk spiderwebs, insect crusts, whatever, then liberally wash them with kerosene and a brush to pick the oily stuff and then let them in the Sun as long as possible (as in days).
Anything you can smell out of them is something that evaporates and contaminates the air around, so let it happen in the yard, not in the house.
If no Sun available, a careful application of a hot air pistol does the same, but not inside home or shop, do it outside or at least in the garage, doors open.

[Enzo]

Every shop has its gross amp stories.

Mine is the nice Yamaha keyboard a lady brought in. APparently their cat got on the keys and sprayed it - that stinky cat spray smell. She was so afraid her husband would get mad at her for what her cat had done, she wrapped it up in a blanket and stuck it in the closet for a couple months. Cat pee just fermenting inside. Then she brough it in for repair.

Of course cat spray is corrosive, it had eaten into the plastic housing, corroded the keyboard contact board, etc. I managed to get it to work, but the thing reeked. I cleaned it as best I could. I told her, when she came for it, that I got it working, but the smell was going to have to dissipate on its own.

[AllAmpedUp]

Success...Amp is back up again...
I installed the new TIP147 (and a new TIP142)....and I made sure the heat-sink was installed correctly....doooohhh....

I also have archived some of the steps on my Droid for a future you-tube video on this subject.

Next:
- Try out a few resistors across the on/off switch to see if we can eliminate or reduce the loud popping when turning amp off.
- But...if that doesn't work, put the speaker toggle back on....lol
- Install the new 8ohm/100w L-PAD power soaker (mostly for the drive channel as I already replaced the Vol-pot for the main channel with a type-a audio)

[J M Fahey]

Cool. Congratulations.
For the power off pop I suggest a .022 or .047uF cap by (at least) 600V, across the opening switch contacts.

[AllAmpedUp]

Cool. Congratulations.
For the power off pop I suggest a .022 or .047uF cap by (at least) 600V, across the opening switch contacts.

I was advised that a resistor would be sufficient, do I need both a cap and a resistor or just one of them?

[J M Fahey]

You need a capacitor.
Just curious: who suggested a resistor?
And, what value?

[Enzo]

Oh, who else? SGM did.

[J M Fahey]

I should have imagined that.

[Jazz P Bass]

I was advised that a resistor would be sufficient, do I need both a cap and a resistor or just one of them?

A resistor & a capacitor in series is called a 'snubber'.
Mostly they are used on relay & motor circuits.
Link: http://www.redlion.net/Products/Grou...Docs/12027.pdf

[AllAmpedUp]

A resistor & a capacitor in series is called a 'snubber'.
Mostly they are used on relay & motor circuits.
Link: http://www.redlion.net/Products/Grou...Docs/12027.pdf

I saw that but was assuming both were not necessary (per another's comments here) .....
Ok, ok, stop laughing at me......and no, the resistor only didn't work, but the on/off toggle still does
At least the new Tip worked...so, after the failed resistor test (I tried 2 separate resistors), I installed the other add-ons
Including (in order after the speaker-out on the pc board) >> speaker on/off toggle >> 8ohm 50w L-Pad >> 1/4 jack to plug speaker into.
This seemed to work as expected but I didn't push the volume before re-assembly
Once all closed up, I tested again but the amp's main channel, didn't sound right....then the fuse blew...
Yep, stop laughing.....I popped another fuse (after 5-10 min)...I felt underneath and the bottom (under heat-sink) was hot...

So, disassemble an then go back to troubleshoot mode (and forget about that dam popping on/off noise and my speaker attenuator for a while)
Once I get new part, I hope it is just a tip again, I will have to test longer (while disassembled) and without any of my "add-ons"...
This stinks!

[52 Bill]

Including (in order after the speaker-out on the pc board) >> speaker on/off toggle >> 8ohm 50w L-Pad >> 1/4 jack to plug speaker into.
This seemed to work as expected but I didn't push the volume before re-assembly
Once all closed up, I tested again but the amp's main channel, didn't sound right....then the fuse blew...

I don't know how you wired all of this, but remember that the speaker output is not directly grounded to the chassis. Did you isolate the jack and L-pad?

[AllAmpedUp]

Hmmm...new part(s) it looks looks like 3 resistors failed: R66 & R65(both 5W .47ohm) and the R72 (5W .22ohms)

Edit:
Double checked all parts, just those 3 resistors were bad....(they are square concrete block looking ones) It makes sense that since I didn't isolate either the L-PAD or the phone-jack there would be grounding issues and that it would sound crappy and that the lowest -impedance resistor(s) would fail.

[AllAmpedUp]

nope....and it worked ok (and sounded ok...) when it wasn't bolted to the housing...
What is the best way to isolate these?

..edit, I have a couple ideas....

[AllAmpedUp]

Going to the supplier at lunch today to grab the resistors/parts...

To solve the root cause (of this failure) I will also pick up some isolation washers (plastic) and a sleeve for the bolt (maybe wire-shrink??)...or even an isolated 1/4 jack (if available)
I assume this will be sufficient to isolate the parts, if not I guess I'll have to build a mount from wood or plastic...
Anyone have a better idea?

[52 Bill]

Insulation washers or plastic jacks will separate the circuit from the chassis ground.

OK, I'll ask the obvious question here, why do you want to add an L-pad and a speaker jack to the amp?