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A Very Compact Hybrid Amp - Page 115

post #1711 of 2213
Thread Starter 
Well ....

This would say that the relay coil and diode are ok.

I guess you're certain that the relay is not closing? With 11.5V on the coil it should be doing something. It has to be doing something.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #1712 of 2213
yes i am certain. there was a definite click when it was working
post #1713 of 2213
Quote:
Originally Posted by runeight View Post
If any of you experience Q1P failures replace this transistors (BC550C) with one of the BC337-25 transistors as used in the ouput stage.
Good news.

I have had another Q1P failure just recently. I replaced it with another BC55 and tried to move the regulator away from it some. So far it's good but, if it happens again, I'll know what to do differently.
post #1714 of 2213
Thread Starter 
Quote:
Originally Posted by Ged View Post
yes i am certain. there was a definite click when it was working
Ged, this is going to get a bit hairy now because on the surface, everything seems to be working properly.

Soooo

First measure again OG, R18L and R19R with respect to SG. The should be all approximately 12V.

If they are then replace the diode next to the relay.

Check the value of R10E to make sure it is 1k.

Then try to power up again.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #1715 of 2213
Did you mean r18r and r9e?
r18 l ,r18r and OG are all at 12V approx
r9e is 2kohms ( cant find r10e)
post #1716 of 2213
Thread Starter 
Nice typing on my part.

R18R and R18L. All those voltages are good.

R10E is next to R13R. Have a look at the silkscreen diagrams on the website to find it. Just want to be sure that it is 1k.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #1717 of 2213
found r10e its 1K
post #1718 of 2213
Thread Starter 
Thanks.

I am now a bit stuck. Here's what we know.

1. OG, R18R, R18L are all at 12V.
2. The LEDs switch from red to green.
3. The voltage across the relay coil is 11.5V.
4. The diode seems to be ok (but we're not certain).
5. The relay coil resistance is 1k balanced by R10E.
6. Everything above is exactly right and the relay should trip.
7. But it doesn't.

I don't know ...

Have you actually tried the amp to see if anything is coming out? I'm grasping at straws for the moment. While I think.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #1719 of 2213
I cant hook it up as the pot and output inputs are not copleted
Shall I buy aa relay and diode and go from there
if there are any other possible parts required please lt me know
post #1720 of 2213
Thread Starter 
I guess this is a reasonable step but I am not convinced that the relay is bad. It's pretty hard to burn up a relay coil, particularly in this situation. And the relay measures correctly.

Although you may want to buy another relay just in case, other possible problems are the diode and/or Q3E. I'm pretty sure that the diode is good too, but may as well swap it out.

So, if you buy a few more parts include Q3E (MPSA14) on the list.

Do you have the stamina to remove the relay and test it with a separate 12V supply?
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #1721 of 2213
have you got any tips to remove the relay
I have a 12 V /5amp power supply any good?
post #1722 of 2213
Yes, stamina indeed is needed to remove a multi-pin component like a pot or relay from a PCB. I've done it w/a good size "solder blob" moved around the pins w/a small flat blade screwdriver prying edges. But this is not something one has fun doing. Easy to destroy the part & damage the PCB/contacts.

But this is a stumper for sure. The relay has a "must-latch" of 9V. And you are measuring > 11V at its activation pins. And this relay worked before. I've not had relays go bad except perhaps for decades-old ones.

My only ideas:

1) Looking at pg#2 PIN CONFIGURATIONS (bottom view) , we are *sure* you've got > 11VDC across pins #1 & #12 and its of correct polarity (+ / -)?

2) And if so, we are sure the relay is not latching pins 4->5 & 9->8 when powered & have checked that w/an ohmmeter?

If both these are the case then I'd think the relay must be bad. One way to hurt relays is heating their pins for a *very* long time - long enough for the internal wires attached to the pins to come loose. BUT the relay passes the coil ohm test (about 1028R). Although this was in-circuit measurement it appears to counter the loose wire idea.

Guess would then be relay is somehow stuck in open position... I'd be tempted to give it a short, sharp wack

Edit: If ordering, be sure you've a BC337-25 Q1P replacement around too
post #1723 of 2213
Thread Starter 
No. It will just be a matter of sucking the solder out of all the holes, patiently.

However, do you have a spare MPSA14 (Q3E)? If you do try that first. No likely but better than pulling the relay for no good reason.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #1724 of 2213
Thread Starter 
Or try some of cfcubed's suggests before replacing the transistor.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #1725 of 2213
measuring across 4 to 5 and 8 to 9 reveals both are open circuits

Is this a bad relay

Thanks guys for putting such a lot of time into this, its really much appreciated
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