Help Marshall vs65r

[Dave H]

I'm reading the manual but I'm not sure that's what you need.
400mv
4v
40v
400v
750v

Are those the AC ranges? If it has a 400mV AC range then it should be OK. Really cheap meters (I have one) just have a series diode for AC and will measure DC on the AC range. You can check by measuring a new 9V battery on the AC range. If it measures something like 20V with the red lead on the battery +ve and 0V with the meter leads reversed then the meter can only measure 'true' AC (current reversing every cycle) not 'AC' riding on a DC voltage (current not reversing)

[nickb]

I think ee established his meter won't work here

AL78- I didn't expect you to interpret the meter drawing quite so literally. No cutting of probe leads is required So long as (1) the capacitor ends up in series with the meter - use clips, wire or whatever and (2) you cannot touch the side that will be probing the amp ( high voltage risk ) it will be fine.

[Enzo]

I do as was described above and I use the free cap lead as a small probe. But for the less experience, I would ground my black probe to chassis then clip a wire to the red probe tip and to the cap, then use another clip wire from the other end of the cap. Now I use that second clip wire as my probe. That way I do not have to hold the cap in my fingers while touching potentially dangerous voltages.


My Fluke meters do not need this trick, but I still wind up doing it now and then when some situation arises. A cap is also a good way to block DC if you want to inject a signal from your generator into the signalpath at some point with DC voltage on it.

[Dave H]

I think ee established his meter won't work here

Right, I wasn't sure what a 'drunk' reading was

[AL78]

Ok guys thanks All as soon as I have the cap I'll tell you.Let's hope I don't explode like Etna this week :-D .Good weekend to everybody

[AL78]

Right, I wasn't sure what a 'drunk' reading was

Lol Numbers flying around on the meter without sense 10 than 59 than 332 in the span of seconds

[nickb]

While you wait, there are a couple more areas you check do that I just thought of.

You can do the signal generator / ACV measurement on either side of C43, and either end of VR4. Also take the PCB out and have a really good look at the V1 and clean tone control stack areas for bad joints.

[AL78]

thanks where i can check easily vr4 or i have to check the vr 4 pot?

[nickb]

VR4 is the clean treble pot. Take a look at the schematic to find connected points - go on it'll be fun and educational

[AL78]

c40 and c 41?

[nickb]

c40 and c 41?

[AL78]

c43 I'm giving 362mv I'get 20mv more or less both sides.
c41 16mv and 9mv c40

I have a question it's R19 the output of the tube?I don't know if we checked either ac or dc

I've checked with continuity test and a magnified glasses the board everything looks good

[nickb]

That doesn't make sense. You apparently have a big signal on C43 but not on C40 and/or C41? That's not possible. Recheck where you are probing

IF we take the C43 measurement of 362mV and IC5 pin 2 at 7mV as correct from earlier, then there is an open circuit between C43 and IC5 pin 2. I would expect around 80mV on IC5 pin 2. Measure the DC resistance from IC5 pin 2 to ground and to the C43/R45 junction.

[AL78]

Sorry maybe I didn't write right I giving 362mv to the input on the amplifier and I get 20mv on either side of c43

[AL78]

So since there was some confusion I've redone the test for c43 I connect the pc with a 1000hz 362mv and I get more or less 20mv(as said before)either side
and I get 16mv for c41 and 9mv for c40.To do the second test (c40 c 41) I had to flip the board because those caps have no room to probe.If you think that the c40 c 41 test is not good Please tell a point where I can check again.I have continuity between Ic5 pin 2 and c43 and r 45.Thanks