5150 hideous death

[The Dude]

There are certainly posts here that you must take with a jar of salt. A grain simply won't do it.

[eschertron]

See, the problem is that the fingers on one hand look a lot like the fingers on the other hand, so the count gets confused.

Anyone who works on amps for a living knows this is a lot of hot air.



Then again, even with my shoes off, I can;t count past 21.

Did you say... :koff: :koff: .. just your shoes off?

[The Dude]

I can't even COUNT...

Maybe should have just quit right there.

[Alan0354]

It would be very surprising to have things burn so bad if the amp is stock. Someone must put a much bigger fuse. I don't believe speaker impedance mismatch will do it unless you use a 32 ohm speaker on an OT for 2 ohm and whale it full tilt.

[Chuck H]

You guys stop picking on SGM! (that's my domain )

Seriously though. It's entirely possible that he's seen a disproportionate number of burned boards in Peavey's and is actually trying to be helpful. And his misinformation about construction and parts availability may be due to his experiences with similar Peavey products and he mistakenly assumed the same problems would cross over to this model. I say this because of my personal experience with those damn black fiber boards in vintage amps. I'm convinced that they are all conductive or will be to a greater or lesser degree. But that's because of my own disproportionate experience with them. The vast majority of techs have seen many more than I have with no incidence. But I'll warn against them every chance I get.

[Enzo]

Conductive black eyelet boards is a problem everyone should be AWARE of. I have found them time to time for years, but MOST eyelet boards are not conductive. I will tell someone to check it, because it is a quick simple test, but I wouldn't rant how all Fender amps have conductive eyelet boards.

SGM has a history here of extrapolating from a sample of one to entire product lines. This is another example of it. Claiming that this happens to a lot of them doesn't further the particular repair, it doesn't suggest something to check, it suggests no diagnostic.


I'll stop picking on him when he stops making shit up.

[tedmich]

every 5150 I've ever owned has had a burnt board EXACTLY like this!

Scientific rigor does not come naturally, and without it I am much more prone to hyperbole and emotional leaps of faith. But it really works best when making and fixing stuff, IME.

I'm currently fighting the nonscientific urge to replace every horrid carbon resistor in this unit with beautiful bulk foil ones (or tantalum!) as I write this.....Urgh! Ack!

[Jazz P Bass]

I had a 100W Carving come in like looking something like that.
They had the board in stock.

[soundguruman]

every 5150 I've ever owned has had a burnt board EXACTLY like this!

Scientific rigor does not come naturally, and without it I am much more prone to hyperbole and emotional leaps of faith. But it really works best when making and fixing stuff, IME.

I'm currently fighting the nonscientific urge to replace every horrid carbon resistor in this unit with beautiful bulk foil ones (or tantalum!) as I write this.....Urgh! Ack!

1. Non- scientific?
2. When the fiberglass turns black, it's becoming carbon.
3. Carbon conducts electricity. Same as a carbon resistor.
4. Follow me so far?

5. The carbon continues to conduct electricity, and the board becomes black-er.
6. It will work for a while, until the carbon shorts it out.

7. The last 2 5150s I worked on were NOT burned. Not every one of these turn black.

8. But sooner or later, the damaged board will become charcoal.

9. The method of using sockets, wiring P to P, is superior. It's the only real dependable permanent repair.

10. Whether or not you accept it, the reality remains. Carbon conducts electricity.

You can use a mega- OHM meter, to verify the leakage between the circuit tracks. It's UN-deniable.
If you choose to ignore what your ohm meter is telling you, than have fun, in your alternate reality.

[Chuck H]

I didn't see where any one was advocating using the charred board. What you're saying is something well known to any half baked tech that's worked on an amp with a arched tube socket, cooked resistor, blackened insulator, etc. I even know of one instance where a fire started because the carbon particles on a fluorescent lamp socket caked up too much and melted the plastic mount, dropping flaming plastic onto the couch beneath it.

[Enzo]

Oh forget him. This is classic SGM bait and switch. He starts by claiming that the 5150s do this ALL the time. Then comes back explaining that charred boards are conductive. But of course that was not the original assertion. Just a form of floor-holding.

[tedmich]

1. Non- scientific?
2. When the fiberglass turns black, it's becoming carbon.
3. Carbon conducts electricity. Same as a carbon resistor.
4. Follow me so far?

5. The carbon continues to conduct electricity, and the board becomes black-er.
6. It will work for a while, until the carbon shorts it out.

7. The last 2 5150s I worked on were NOT burned. Not every one of these turn black.

8. But sooner or later, the damaged board will become charcoal.

9. The method of using sockets, wiring P to P, is superior. It's the only real dependable permanent repair.

10. Whether or not you accept it, the reality remains. Carbon conducts electricity.

You can use a mega- OHM meter, to verify the leakage between the circuit tracks. It's UN-deniable.
If you choose to ignore what your ohm meter is telling you, than have fun, in your alternate reality.

As a chemist I understand that carbon conducts, yes. Thats why I etched a new board. My preference is to avoid mixing PTP with PCB. I originally posted because the burning was extreme; I could find no other posts or pictures with a comparably burned 5150 board. You stated that these were common in your experience. Others did not agree. Thanks for the input!

[Jazz P Bass]

And SGM enjoys proselytizing.

[Chuck H]

Just a form of floor-holding.

Screw that! I am the all knowing, all seeing "Chuck H"!!!...

"Oh wait, Enzo's here?... Never mind"

[Alan0354]

As one that designed pcb for years and used exclusively pcb in my career, I do not think FR4 pcb is inferior to wired boards. PCB do not burn easier than wired boards. It's all about the person that layout the board. I layout high current boards into amps of current, I layout boards for 10KV+. It is all about the layout technique. Don't blame on the pcb for incompetent designers.

Many ignorant pcb designer use too thin a trace, putting high voltage traces too close together. When you have high current trace going from one layer to the other, you need double or triple vias. Some people use heavy trace but only one via to go to different layer, you burn at the via!!!! This is no different from using too small wire for high current signal!!!

As for conductive fiber boards, I have no experience. But I have a lot of experience of conduction of materials with high voltage. In high voltage design, there are two distinct issue of conduction. One is insulation and the other is creepage.

1) Insulating resistance is very easy, most non conductive dielectric is in the ball park of 400V per mil. A piece of paper can insulate hundreds of volts easily. In real life, this is really not an issue as long as you design for say 100V per mil.

2) Creepage, which is current travel along the surface of an insulator due to humidity and contamination. This IS the big issue with leakage and arc through. The number depends on the material, humidity, flux and all sort of contaminants. I have to get the book to know the general number. This is spec in CE test manual. I personally do not believe the fiber material have conductive issue, more because of the flux on the surface, the moisture it attracted on the surface that cause the problem. I can tell, Fender do not clean out the flux on the fiber boards, if people start monkeying with mods, they add more flux on the surface every time they solder stuff on. I think that's what's happening. Scrape the flux off the surface when the flux solidified and see whether you can fix the leakage.

I don't know the circuit of the burn board, it's hard to comment. Does that part have high voltage or current? If it is high voltage, then look for creepage path. I route channel between two pads with high voltage differential to eliminate creepage. If it is current, look for bottle neck along the signal trace. Don't generalize and make assumption.