70s Ampeg V4B Blows Fuses

[ca7922303]

This one measures 0.5v/311v.

[ca7922303]

R52(587v/9mv), R53(620v/5mv).

[ca7922303]

I'm guessing the resistor that measures 311v/0.5v is the one that popped causing vdc to go to mvdc?

[vintagekiki]

This resistor measures 620v/311v.

What you are showing are 100k / 2W resistors (most likely R56, R57)
The voltages you measured (620v / 311v) are OK because the resistors are connected in series.
Compare the detail that you show with the schematic, and it will be immediately clear what is about.
For R52, R53 (4.7k / 2W) use schematic and find them.

[ca7922303]

Only other resistors off the board are these two. They both measure 4.7k resistance and 570v so I'm wondering how they be an issue?

[vintagekiki]

Only other resistors off the board are these two. They both measure 4.7k resistance and 570v so I'm wondering how they be an issue?

Somewhere you wrong in measuring or interpreting schematic.

[ca7922303]

Not sure what you mean?

[ca7922303]

Yes R52 & R53 is 4.7k 2 watt resistors.
When measuring the voltage, in which position is SW₄

Standby switch is in on position.

[ca7922303]

Somewhere you wrong in measuring or interpreting schematic.

Not sure what you mean? Can you explain further?

[vintagekiki]

Not sure what you mean? Can you explain further?

OK. Let's go step by step.
Checking how the power amp works.
Follow the schematic.
Connect speaker to J6 SPKR
StandBy (SW4) in position ON
Measure and upload the voltage measurement results at points 1, 2, 3, 4
Remove V201 (6K11) to turn off the preamp.
Plug the guitar into jack J4 or J5.
If the output stage is correct you should get a clean guitar sound of the order of 10-15W
Descriptions of how the V4B responds.

[g1]

Do you have the resistors like in the bottom right of this pic?

[vintagekiki]

He only has good will and time to lose.

[ca7922303]

Do you have the resistors like in the bottom right of this pic?

Yes, I will post a photo, but they both meadmea 4.7k redisresis and 570v
Don't see how they could get causing the issue and they seem to be connected to impedance switch. Can you explain how they are connected to R52,53 on board? Thanks for your help.

[vintagekiki]

... ...

Compare the layout of the V4B in front of you with the schematics
Look where all the wires are going from R52, R53

[ca7922303]

Do you have the resistors like in the bottom right of this pic?

Here's the photo