Fender M-80 chorus problém

[warry]

It's incredible!
Tonight, I retested all TIP147 TIP 142, and found that Q8 and Q9 were shorted.
So I alternate these two transistors again. I think this just a test I had done before finishing my current limiter. So sorry you have taken to the wrong runway.
After the exchange of Q8 and Q9, I switch on WITH the current limiter, and Ohhhh miracle bulb shines feebly.
So I just take all the values that I put above:

TP1 = 22.23 VAC
TP2 = 22.23 VAC
TP3 = 26.80 VDC
TP4 = -26.76 VDC
= 15.50 VDC TP5
TP6 = -15.74 VDC
TP7 = 7.36 VDC
TP8 = -7.53 VDC

TP28 = 15.26 VDC
TP29 = -17.38 VDC and 6.5 MVAC
TP30 = 7 MVAC
TP31 = -0083 VDC
TP32 = 17.19 VDC
TP33 = -17.23 VDC and 23 MVAC
TP34 = 54 MVAC
TP35 = 0.003 VDC

[vintagekiki]

Enzo says: check R127, R128, CR20, CR21, CR22, CR23, R130, R129.
If any of these component defective, the (quiet) current through the output transistors is high, and fuse (XF2 or XF3) blow.
If a defective one of the output transistor, always check R138, R139

[J M Fahey]

Salut warry, je vais essayer de traduire ça que Enzo et VintageKiki ont écrit.
*OK, then most likely both positive and negative side power transistors are turning on at the same time.
** C'est très possible que les transistors positifs et négatifs conduissent courant au même temps (vous pouvez avoir un problème grave de bias/polarisation)
*There are two powr amps amps in this - only takes one to blow fuses.
**Il y a deux amplificateurs ici. Quelque un d'eux "brûlé" fera sauter les plombs/fusibles
*In the upper half of the drawing, look just to the right of the IC U12.
** Regardez la partie supérieure du dessin, à droite du CI U12
*From top to bottom, there is a string of parts. R127,R128, CR20,CR21,CR22,CR23, R130, R129. Are ANY of those open? DO all four diodes test as diodes?
** De la partie supérieure vers la inférieure vous avez une chaîne de composants.
Cette chaîne est très importante, parce que elle fait deux choses:
1) elle fournit le bias aux TIP142/147;
si "CR20,CR21,CR22,CR23", quelq'un d'eux est ouvert, les TIPs conduisent trop et brûlent; mesurez qu' ils sont toujours des diodes
2) elle va définir la tension de sortie statique, sans signal.
si R127+ R128 = R130 + R129, tension de sortie= 0V (ou un très faible valeur)
si R127 ou R128 sont ouvertes= -40V à la sortie
si R130 ou R129 sont ouvertes= +40V à la sortie
*Now go through the lower power amp checking the corresponding parts.
**Essayez le même dans l'autre amplificateur.
Bonne chance .... ou Merde !! , ça que vous préférez.

[Enzo]

That is what I meant to say, I am sure.

[warry]

Hello,

I'm sorry, I was on holidays (Australia is very nice). But today, I have the same problem with my M-80. Are you OK to help me again?

Thank you

[vintagekiki]

To start ... ...
Read this topic again from the beginning of the problem

[warry]

To start ... ...
Read this topic again from the beginning of the problem

OK I read the topic.
And after... What I have to do?

[vintagekiki]

Enzo says

If CR52 is shorted, please change CR53 at the same time. Even if it tests OK now.

When CR52 shorts, it becomes liike a piece of wire. ANd that leaves CR53 directly across one end of the transformer winding to the other. This can be very stressful on the part. SO for the low price of a new part, replace it - that will improve reliability of the repair.

before you put the TIP142/147 parts back in, make sure they are not shorted. If one of those failed, it could be responsible for the failure of CR52.

Please make sure the flat mounting tab of the TIP142/147 transistors is not shorted to the heat sink. They MUST be insulated.

OK, then most likely both positive and negative side power transistors are turning on at the same time.

There are two powr amps amps in this - only takes one to blow fuses.

In the upper half of the drawing, look just to the right of the IC U12. From top to bottom, there is a string of parts. R127,R128, CR20,CR21,CR22,CR23, R130, R129. Are ANY of those open? DO all four diodes test as diodes?

Now go through the lower power amp checking the corresponding parts.