Another MARSHALL Valvestate 2000 AVT150 Blowing fuses......

[blearyeyes]

The tall ones are electrolyte aluminum radial?
The flat square ones are? Film?
And the little orange ones are?

[blearyeyes]

C3&5 47uF 63v 85c
C2&4 10n 63v
C1 22p 50v
C6 10p 50v

This is what I am trying to order but hey! What are they? Picture above.

I'm sorry this is out of my area of expertise. I'm a complete beginner here. There are tons of different kinds of caps on Mauser.

And dude I gotta finish this somehow, didn't mean to be rude dude..

I understand the spec just not the type of capacitor.

[52 Bill]

No. I don't think I should remove all 12 caps on the modules to test them. I read..... and correct me if they were wrong... that using a standard ohm meter, if you get a reading of Mohms, short or open the cap is bad. Normally you should get a reading in the low Kohms range.

I this is a bad way to proceed let me know.

While there are ways to "test" caps with an ohm meter, this is not a reliable test. A cap should never really show a steady resistance value. What happens is the test voltage that your meter uses to read resistance, charges the cap up. The small values charge and discharge very quickly so they will normally always read as open circuit. The larger values charge slower and you can see the resistance rise and fall as the cap charges or discharges through the meter.

If any of the caps reads a steady resistance value retest by reversing the leads and then test out of circuit.

The tall blue cans are electrolytic caps, the blocks are probably mylar film and the little ones are probably ceramic discs.

[blearyeyes]

Thanks Bill.

[The Dude]

C3&5 47uF 63v 85c
C2&4 10n 63v
C1 22p 50v
C6 10p 50v

This is what I am trying to order but hey! What are they? Picture above.

I'm sorry this is out of my area of expertise. I'm a complete beginner here. There are tons of different kinds of caps on Mauser.

And dude I gotta finish this somehow, didn't mean to be rude dude..

I understand the spec just not the type of capacitor.

Not taken as rude. Nor was I trying to be rude. I posted the link to assist you with checking your caps. Since you posted saying you were using an ohm meter rather than a cap tester, I assume you don't have a cap tester available. The article/link I posted will help you know what you are supposed to be getting for readings. You can not accurately test caps in circuit. Much of the time, you will be reading across other components. The fact that you had different readings from module to module can mean several things:

1) You do indeed have a or some bad caps and you need to remove them for a more accurate test.
2) You are reading across other components since the caps were in circuit when you tested them.
3) Some of the caps were holding more or less of a charge than others.
4) etc.

Solid state components make up far more failures than shorted caps in most gear. The most common failure of an electrolytic cap is drying out which causes the cap to have less capacitance. They short far less frequently. I have given you this information, not to be rude, but more so to suggest you look at the more likely failures first. It seems to me, again not trying to be rude, that throughout this thread you first suspect shorted capacitors when that makes up a small percentage of amp failures.

[blearyeyes]

I have a small Extech multi meter with auto ranging.

It does have a setting with capacitance readings.

I'm trying to do as little soldering damage to these boards as possible.

[The Dude]

If you're going to be replacing the IC's anyway, pull out the old ones and then test the caps before you install the new IC's (with no IC installed and the module unplugged). Then, report what you find.

[Enzo]

If you have a shorted IC on the little board, and try to measure the caps, they will seem shorted also, because they are wired to the IC.

As Dude says, remove the bad IC and check caps on the disconnected board.

For the record, I have never had a bad cap on those little boards.

[blearyeyes]

Thank you Guys. I read up online regarding testing caps and it is more than just sticking a meter on them. I'll pull the ICs today and see If any caps seem bad.

[Jazz P Bass]

When testing a TDA IC , without any power applied, a faulty one will have continuity between the power pins (one or both) & the output pins.
Pin 13 & 15 are power & pin 14 is the output pin.
A brand new IC will measure in the megaohm range.
A bad one (worse case) will read a direct short.

[blearyeyes]

All caps acted as they should. Drained them, Replace ICs and found a trace had been pulled up last time. I made a jumper. Drained all caps in power supply re- installed power modules fired up amp and bulb was dim.
I didn't understand caps. Also when and if you run into another newbie like me, tell them to buy a magnifying headband right after building the poor mans lightbulb limiter. Lol.

Going to plug in a speaker and test.

Dan.

[blearyeyes]

Huh...... no sound.

Probably something to do with my work.

These little power modules also have a third layer with a trace running to the output pin. .......... From the output of the ICs.

[blearyeyes]

Hooked up effects loop out to little powered speaker and the preamp is working fine. Which means the tube is ok.

[blearyeyes]

Reversed c189 and c230 into the modules and screwed on the rest of the nuts to the ins and outs on the back for grounding and everything is working!

It is fixed!


You guys have a lot of patients and I appreciate this sooooooo much you have no idea.


Thank you!

[DrGonz78]

Man oh man what an epic thread!! Sorry I could not add much here! Still I was rooting for you all along the way, I remember at one point you said you gave up. Something in me knew you were not gonna give up or we would only have a bout 30 posts on this thread. Just wanna say you did a great job! These types of amps are a bitch to work on!! You were patient in the end by not wanting to remove the caps to test them out of circuit and that was a smart move. Now you know that those caps are not the most likely suspects either.

In this case it seems that some caps were reversed?? Clarify some more on exactly what you think happened here as I am very curious to know the whole story. Either way Good Job DUDE!!!

Edit: You must tell all that there was a bad trace.... Which you did... But then you say that you reversed some caps? Explain a bit more for all to understand>>> ME at least. LoL Good job!