Help Marshall vs65r

[AL78]

Hi first time here.So a friend of mine give me this amplifier with this problem.No sound noise the volume and any other thing doesn't change the noise.So I noticed that the 2 big resistor(white) on preamp board go really hot.I checked them and the values are ok.So looking on internet someone tells is a problem with the power transistors.I pull them out I checked with my digital multimeter and they both give values under .6v just one pin of the t64a is .623. All the value are different are those transistor gone?Do make sense to make the transistors the wrong components?Thanks

[Jazz P Bass]

0.6V is a good reading if it reads only one way.
When using the 'diode check' function of a volt meter to check a BJT transistor the meter leads should be set as follows.
For NPN type: Red (+) lead on Base to (Black) Emitter. (Red) Base to (Black) Collector.

For PNP type: Black (-) lead on Base to (Red) Emitter. (Black) Base to (Red) Collector.

All other lead/pin configurations should read open circuit.

Large resistors are meant to get hot.
That is why there is a maximum wattage rating on them.
Measure the voltage drop to see how hot they should be getting. (P=VxV/ R)

[AL78]

thanks.Do you have any idea what this amp must need to work?it powers up there is hum and if you move volume nob in both channel nothing happens

[nickb]

It could be a bad switch on the FX return jack. Try plugging a jack intio it a dozen time to try to clean the contact, or connect the send to the receive with a lead. Google "Dreaded switching jack problem"

If that doesn't work you can test the power amp on it's own by plugging your guitar into to the FX return.
Still nothing? Listen up close the the speaker, there should be a faint hum.
Still nada? Test the speaker.

[AL78]

no the amp went down while playing(not me it's a friend amp).It's not the speakers nor the send fx etc.There's hum on the speakers and sometimes noise

[nickb]

no the amp went down while playing(not me it's a friend amp)

So? They always work and then stop. You have to do the diagnostics to narrow down the fault. You may well be right in that it's the power amp but you need to be certain otherwise you are putting your effort in the wrong place.

[AL78]

nothing changed

[nickb]

Hum and noise on the speaker is a good indication that the power amp is OK.

Have you tried plugging into the FX return yet?

What about taking the line out to different amp?

Schematic http://bmamps.com/Schematics/marshal..._vs65r_65w.pdf

[AL78]

Of course nothing comes out

[nickb]

Of course nothing comes out

Seriously AL78. You need to up your game - I can't play guessing games with you. Nothing comes out of what under which test?

[AL78]

No sound comes out from the speaker only hum I've done all the test you told me to do again ALL the test.

[nickb]

No sound comes out from the speaker only hum I've done all the test you told me to do again ALL the test.

What about the line out to a different amp test?

[AL78]

As stated before done the test from line out and no sound come out from the othre amplifier

[nickb]

OK. Gotcha. Let's measure some DC voltages to ground. I like to use the sleeve of the input jack as a handy ground.

1) Collector of T9
2) Collector of T11
3) TIP of speaker jack
4) GATE of J111 T16
5) Pin 4 of IC7
6) Pin 8 of IC7

[AL78]

Thank for your patience.Listen Here in italy is kinda late so I'll do it tomorrow.I kinda new at this for "to ground" do you mean that iI have to touch with my red lead the point you said me and with the black lead the chassis of the amp? I have no idea what's the gate of j111 t 16.Last there is no speaker jack the are faston on the speaker side and the red and black are soldedered on the amp board.