It's always a good handrule to start with trimmers in center position.
The circuit will have been designed for a point not far from that.

DON'T use the markings on the board for capacitor polarity reference. They are not always correct! Actually, there
are quite a few typos and misprints in the silk-screen.
I normally advice to replace one component at a time, using the old component for polarity reference.
You probably have a good photo, that you can use for reference, that'll be fine too.

Anyway, I think, I would have diagnosed and repaired the bad amplifier module before upgrading and
replacing a lot of components.
If the new components doesn't cure the original fault, and you've inadvertently introduced a
new fault somewhere, it could end up a very difficult situation.
And in case the amplifier module turns out to be a complete write-off, you've lost money and time too.

Martin

StuckE30 wrote:

all I'm waiting on now are the red Wima's.

Those are not electrolytic capacitors (and neither are the rest of the plastic foil caps regardless of external colour). Replacing them will do no harm, but most probably is just a waste of time. They don't age.

Keep the ones you removed, you'll need them somewhere else some day 🙂

tournedos wrote:

Those are not electrolytic capacitors

Well, C1, C2, C5 & C25 (which are referred to) are actually electrolytic caps.

Well its a little late to look at each component and replace them one at a time. I desoldered everything in one pass and then went back in to solder the new stuff in. I guess I will just have to cross my fingers and see what happens regarding the capacitor polarity. I did put them all back in according to the PCB silk screening. I have a few pictures yes, but I don't think any are sufficiently details to determine polarity of each component... but I do have the second working and unmolested amplifier I can look at. It only takes a minute to pull it off the other tower.

I'm pretty confident that replacing the trimmers and resistors is the problem, but that is based largely on experience I've seen with other identical units. Really I cannot *see* anything else bad, and I do not have the tools or experience to make a diagnosis beyond that.

While you have a point on the potential waste of money by throwing money at all new components in hopes it will just fix it... It's only $35 USD or so for the parts, and a little of my time. If it doesn't fix it I have no regrets, I've still had a bunch of fun and its a learning experience.

BO wrote:

Well, C1, C2, C5 & C25 (which are referred to) are actually electrolytic caps.

Oh, they are bipolars! Definitely worth replacing then.

Carry on, I'll get me coat 😁

You should at least check rectifiers, diodes and the transistors, connected to the burnt resistors, I have never worked on pentas, but this kind of resistors are present in other amps, and I never found a bad one

Well checking them would be nice... but I haven't the slightest idea what to check for. If anyone cares to teach and its something I can check with a DMM then I'm all for it. Otherwise I'm a risk taker heh...

During initial power up for setting the trimmer pots would it be "safe" to run the amplifier no-load without the fets snapped onto the heatsink? I suspect they aren't going to get hot and burn up if there is no driven load.... but then what do I know?

It's just a bit of a hassle to stuff all the contents of the heatsink housing back into it, especially if its just going up in smoke again....

StuckE30 wrote:

If it doesn't fix it I have no regrets, I've still had a bunch of fun and its a learning experience.

That's the spirit.

StuckE30 wrote:

During initial power up for setting the trimmer pots would it be "safe" to run the amplifier no-load without the fets snapped onto the heatsink?

Absolutely no!
They MUST have normal operating conditions.
The FETs will not blow but their HFE depends greatly on their temperature and anything you adjust without heatsink
you'll have to do again with heatsink. - If you can get a stabile setting without heatsink at all, it's usually all over the place.

Martin

Pretty disappointed. Package showed up from Mouser a day late with the red Wima's, and the 10uf C25 caps are huge. Don't know how I missed them being 30mm lead spacing instead of 5mm like the others... oh wait its because Mouser didn't have the info filled in so it turned up in the same search criteria...

Sigh. Unfortunate as the cost of shipping the two replacements will be triple the price of the actual capacitors... that and no chance of getting this calibrated and tested this weekend.

Edit... and the ones I need are on back order. Seriously... Sigh.