My fender stage 185 amp won't power up

[DrGonz78]

If the bulb is now dim in comparison that would be a good thing, depending on how bright it is. I would imagine that if the transformer had a dead short that bulb would be lighting up very bright.

[The Dude]

It looks like CR50 and CR51 are shorted. Pull one end of each and check out of circuit. CR52 and CR53 read what I would expect in circuit. If they check ok out of circuit, you may have shorted outputs or something else on the +50V rail.

[DrGonz78]

Also to note CR52 & CR53 are not open they have higher resistance but the meter did give an open reading. The dude is right that you should pull one lead on each those shorted diodes to make sure. If it hard to reach both end of the diodes then you may have measured shorts(Continuity) where the bridge is connected to both sides. That is tough to explain but look at the schematic and you will see how CR50 connects one lead to CR52 and CR51 connects one lead to CR53. It could lead to confusion so taking the board out to remove one leg on each diode will prove it for certain.

[spindarec]

CR50 is shorted, i've pulled it out of circuit and my tester shows in test diode that its open in the two ways. Cr51 is a bit burned to IC side, in diode test I got 1 in one side and 500 to the other side. It's the same for CR54 and CR55. Why I don't have 0 on my meter ?
I will replace CR50 on tuesday but do you think this short doesn't hides something else ?

[DrGonz78]

Well when testing in diode setting and it goes to "I" as infinite resistance I think. As I understand, it is not a number 1 but a letter I. Just replace the part and see if you have your 50v power rail back working again. Do error on the side of caution by connecting it up via light bulb limiter.

[spindarec]

thank you DrGonz78, we're monday and shops are closed in France every mondays. won't wait t'ill tomorrow ;o)

[J M Fahey]

we're monday and shops are closed in France every mondays.

Weird.
*All* shops?
Why?

[spindarec]

When I say all shops, I'm not talking about mails and supermarkets, but yes ,in France, most of the shops are closed every mondays because they're opened on saturdays… Weird you say ? Maybe but we're like that Frenchies

So, i went to my component shop this morning and bought two 6A diodes in replacement of CR50 ( two for spare, I only need one). Then actually, i'm doing a test with the lightbulb limiter and, wouahooo it's not " shining bright like a diamond ". I've recovered the +50V line and the channels/boost leds in front of the amp are shining too !!! Can I connect it to the speaker for a test or i got some checks to do before ?
Can't wait

[g1]

Do not connect any speaker until you verify there is no DC voltage at the output connections.

[spindarec]

There's no DC voltage on the speaker output, so iv'e made a test, playing 2 hours long. At the end of my session, i had to move the jack to the input of the amp to recover a nice output signal. No weird noises, no buzzes, but just like if the output signal was not full. I'll check tomorrow if it's the same with the two jack sockets. If it is, what should I do ? thanks.

[The Dude]

Are you still on a light bulb limiter? If so and since you have no DC out of the amp, go ahead and ditch the limiter and try the amp as it would be run normally.

[spindarec]

i did it "The Dude" but at the end of my session,I had low gain to the output, not enough treble and meds. Could it be a problem on the preamp circuit ?

[The Dude]

......At the end of my session, i had to move the jack to the input of the amp to recover a nice output signal......

Can you elaborate on this part. I'm unclear as to what you mean. Are you saying you bypassed the preamp and went straight into the power amp or something else?

[spindarec]

No, I've bypassed nothing. I mean at the end of my session, at many time the volume became lower with a loss of treble and mids. The solution was to move the jack to the input to recover a full signal to the speaker. I don't think it comes from bad jack wire or jack socket. This amp makes me crazy.:/

[g1]

The solution was to move the jack to the input to recover a full signal to the speaker.

What do you mean by "move the jack"? Do you mean wiggle the cord where it goes into the input jack?
You were using the same input jack for the entire test, weren't you?
Or did you have to move the cord into a different input jack at the end?