Fender M-80 chorus problém

[warry]

Hello,

Just for tell you news.
I don't found diodes 6A4, but 6A6. I think like we say in french "qui peut le plus peu le moins" (He who can do more can do less). What do you think about?
I found the TIP147 and TIP142.

Thanks

[Jazz P Bass]

6A6 diode

Yes the 6A6 is more is better.
Rated for 600 volts.

[warry]

big deception...

I changed the 4 diodes, the TIP147 & 142.
I controled the C83, its ok.
But I have exactly the same probléme... XF3 burned.

When I take the tension, I have TP1=TP2=34V (for 29.9 in the doc).
I can't give you the others values, because the fuse burne immediatly.
I star to think it's come from transformer....

Ah I controled the CP14 for see if it's at the ground... I had invariables values.

So if you see.

Thank's

[Jazz P Bass]

Amplifier Test

Amplifier power supply voltage check.
Remove the output transistors. (Q8 & Q9)
Check all transistors in the output section for an internal short.
Measure resistance to ground from TP3 & TP9,TP5 & TP6, TP7 & TP8 (greater than 1K ohm is good)

If all is good, turn on power & measure each voltage test point Vdc to ground.
TP 1 & TP 2 verify Vac from transformer.
If all is good than it is time to repair the output section.

[J M Fahey]

Hi/salut warry.
Agree with JPBass and add: build a Bulb current limiter ( limiteur de courant a lampe) which will let you measure some without the fuse blowing (vous pouvez mesurer quelque chose sans brûler le fusible).
Do what he says but plugged into the current limiter (faites ça qu'il dit mais connecté dans le limiteur)
I'll also post how to measure TIP142/147, which are somewhat different because they have a reverse diode and they are Darlingtons (moi je vais poster aussi comment mesurer des TIP142/147 car ils sont Darlingtons e ont des diodes inverses de protection)
Mon mauvais dessin du limiteur:

[Enzo]

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

[warry]

If all is good, turn on power & measure each voltage test point Vdc to ground.
TP 1 & TP 2 verify Vac from transformer.
If all is good than it is time to repair the output section.

I don't understand all... sorry.
But I tested the TP 1 & TP 2 Vac, I found 34V (for 29.9V in the doc)
After, I can't verify the others TP (Vdc) because, the fuse burn

What do you want to say, when you write :"If all is good than it is time to repair the output section"

[Steve Conner]

Bof, baguette, etc.

What do you want to say, when you write :"If all is good than it is time to repair the output section"

C'est a dire: Si les diodes et transistors que vous avez remplaces sont tous bons, aucun n'est monte a l'envers, et si vous n'avez pas oublie les rondelles isolantes entre les transistors et le radiateur, mais le fusible brule toujours...

Ca indique peut-etre une faute plus subtile, qui demande aux transistors de sortie de passer trop de courant. Dans ce cas il faut controler tous les autres petits composants dans l'ampli de puissance (="Output section") vous trouverez peut-etre une resistance brulee, etc.

[warry]

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

Hi Enzo... I'm very interested by what you say.
My TIP142 & 147 are all on a radiator. But there is a screw.
Normaly, I must not have a short between the radiator and the little slabs of TIP 147/142 ?
I will make pictures this after-noon for to be clear.

[Steve Conner]

Hi Enzo... I'm very interested by what you say.
My TIP142 & 147 are all on a radiator. But there is a screw.
Normaly, I must not have a short between the radiator and the little slabs of TIP 147/142 ?

Yes! A short there is bad, the power supply is shorted to ground and the "fumee magique" will come out

[Jazz P Bass]

Power supply test

I don't understand all... sorry.
But I tested the TP 1 & TP 2 Vac, I found 34V (for 29.9V in the doc)
After, I can't verify the others TP (Vdc) because, the fuse burn

What do you want to say, when you write :"If all is good than it is time to repair the output section"

You need to get the power supply operational.
Remove the TIP output transistors.
Measure the resistance of each test point to ground. (above 1K ohms is good)
That is what I meant by "if all is good" (above 1K ohm)
The resistance check to ground will tell if the voltage rails are loaded down or not.
Some low resistance is "burning" the fuse.

[J M Fahey]

And please *do* build and use the bulb current limiter or you will never be able to measure anything. (vous devez construire et *utiliser* le limiter ou mesurer quelque chose deviens impossible)

[warry]

And please *do* build and use the bulb current limiter or you will never be able to measure anything. (vous devez construire et *utiliser* le limiter ou mesurer quelque chose deviens impossible)

I am willing to make the current limiter that you propose. But sorry, I did not understand your plan.

So the last news: I removed all the TIP 147 & 142. And ... the fuse doesn't fuse!!! And when I tested the TIP, I found one TIP142 and one TIP147 shorted.
Maybe, it's come from a short between the TIPs and the radiator. So you confirm. The TIP have to be maintained on the radiator, but without short between them.

[J M Fahey]

OK.
Build the current limiter before doing anything else.
After you do that, we go on.
Meanwhile, get 4 fresh output transistors, new micas, grease, insulating nipples, screws.
Plug *nothing* before you have the limiter.
Construisez/montez le limiteur avant tout.
On ne va suivre sans ça.
Achetez 4 TIPs, nouvelles micas isolants, tuyaux plastiques isolants (nom français?), graisse thermique, vis, une lampe 220V 25W ou 40W, tout en somme.
Ici le plus coûteux n'ést pas le composant mais le temps.
Tranquillise toi, je crois que toi tentes de faire tout très vite.
Comme parlait Napoléon a son assistant: "Habille-moi lentement, car j'ai peu de temps" ou quelque chose comme ça.

[vintagekiki]

Remove the output transistors on both channels Q8/9 and Q12/13 . XF3 burned again or no?
Before starting voltage check with ohm meter that there is no short circuit between the chassis and TP4 (-40VDC) or TP3 (+40 VDC).
TP1 = TP2 is alternating current test point (~30VAC)
CP14 is ground (chassis) point.
With removed output transistors on both channels, and corect C82/ C83 (4700μF/ 50V) fuse XF2 or XF3 should not be burned, and voltage on test point must be correct (+/- 40VDC)
All output transistors must be insulated with mica insulators.
Output transistors Q8/9 and Q12/13 must be matched.
If output transistors are correct, set and put in the work channel by channel (not both simultaneously)
With removed output transistors on both channels Q8/9 and Q12/13 and not burned fuses (XF2/ XF3), voltage on test points TP31 or TP35 must be some mV (... +/- 10-20mV)