Fender Blues Deluxe troubleshooting? FIXED! How to Dumblize?

[tubenoob]

Good morning,
After my success getting the Vox tremolo working
I've decided to tackle the pile of broken amps I have here.
Can anybody help me figure this out, I have a Blues Deluxe here that lost power while I was playing, it faded out and now it's dead. I'm not really sure where to start.
I measured plate voltage, tested the tubes, looked for anything burnt and haven't found anything obvious.
What kinds of things would cause it to lose power, fade out and go silent?
Thanks

[Reeltarded]

No burn marks anywhere? Check on the tube board real close.

They don't use black resistors at the factory.

Anything?

[tubenoob]

I pulled the board and there are no burn marks or anything that looks suspect...hmmm

[Leo_Gnardo]

There's a pre out/power amp in pair of jacks on the side of the dashboard near the power switches right? FX send/return same thing. Signal often gets lost as the metal slowly corrodes on switch contacts inside the FX return or power amp in jacks. Exercise the contacts by plugging a cable in (power off please) repeat a dozen or so times, that may get the signal going where it should.

Also, there's a jack on the bottom of the amp for an extension speaker? Another set of contacts decides whether you're using the 8 or 4 ohm tap. Years of corrosion here will also stop the signal from your output transformer from getting to the speaker. With amp unplugged from power line, you can poke the jack with a finger, while spraying non-residue contact cleaner on the contacts. I often burnish these contacts with super fine sandpaper, 1000 grit works wonders.

If you do these & still no joy, write back & we'll look at some other suspect areas. For instance input jacks that often come unstuck from the PC board, you have to unass the whole board to resolder or replace, what a hassle.

[Stevem]

What is the negative voltage on pin 5 of either output tube, above -52?

[matt h]

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[tubenoob]

Ok, sorry I had to leave for a bit and miss these replies.

Here are all the details I can think of.
I mean lost power as in faded out while it was working, but let me back up and fill in more details.
My friends says his amp lost power and quit working and also had a broken input jack and I say bring it over let me take a look.
I get the amp plug in and it seems to work fine so I replaced the input jack and notice two ceramic 5w resistors on the board look toasty so I replace them.
I bench test it and it seems fine, I put it back together and discover that at a loud volume it has a crackling distortion that is triggered by the vibration of the combo cab.
Guessing at this point, I replace all the filter cap (this may have been un-needed) put it back together and the crackle is still there with vibration only but now I notice it's more of a crackle/cut-out and I see the distortion channel LED flickering with the noise/effect.
I prod the power supply caps with a chopstick and the power/sound fades away to silent (like the original complaint) and now I have no signal passing.

What do you think?

[matt h]

(deleted)

[tubeswell]

The PC boards on these are total crap and the traces break at the slightest provocation. You probably have a broken trace or two that will take ages to hunt down and repair, and in the process you'll quite possibly break some more traces and board jumpers. Best advice I can think of is gut the chassis and build an eyelet board or turret board-based amp.

[Phil_S]

It is a good excuse to remove the PC boards and build a real amp in there!

[tubenoob]

That would be a better solution. This thing is a total POS.
I would love to turn it into a real amp but it's not my call.
So what's the fix, look for broken trace and bypass with wire?
Is there anything that can be done? What's the deal with the relays?
Are those dropping resistors for the relay power or why do they get so hot?

[Leo_Gnardo]

Are those dropping resistors for the relay power or why do they get so hot?

Those roasty 5W ant coffins are for plus and minus 15V powering the reverb drive & return IC and FX send & return IC, mini DIP relays too. They're dropping a lot of voltage, that's why they get hot. V squared over R = watts dissipated in the R.

Didja have a look at aux speaker jack yet? We'd hate to see you haul that big board in & out then find the problem isn't on the board. (Put slap forehead with palm smiley thing here.)

Also have a well lighted scan of the tube-socket PC board. They like to unsolder themselves too. Then there's the rare possibility of a pre tube that has an open or intermittent filament. Seen that happen too.

[tubeswell]

That would be a better solution. This thing is a total POS.
I would love to turn it into a real amp but it's not my call.

Well you are the tech - make it your call. Tell the guy the scenario. Tell him it may cost him for 3 hours or more labour to find the broken trace/jumpers and that even then you won't be practically able to guarantee the repair. Tell him its far better to rebuild it and make it better and more reliable. Pique his interest in you pimping the circuit for him to have the amp of his dreams. Sell him some options.

I'm not advocating ruthless consumer exploitation here - rather it it were me, I'm not happy fixing mass-produced shite anymore because of the endless comebacks. I'm far happier doing rebuilds which I can guarantee will last for a fixed period (subject to properly implemented periodic tube changes, and not abusing speakers etc).

[Phil_S]

It seems to me the "proper" repair is to replace the suspect PC board. Parts and labor could end up costing about as much as gut and rebuild. I dunno if I'd want to stand behind a repaired trace, particularly if I wasn't sure it was the only one! Don't help the customer kick the can down the road without being sure he understands completely what that means. It means he's spending money now and spending more later.

[tubenoob]

Hmm good advise I'm sure.
I had to take a break but I'm still looking at this thing, I haven't tried everything suggested yet but thanks for all the comments!

I'll be back....I hear y'all thinking greaaaate.... Lol