Fender BJr repair

Amp Mad Scientist said:
I want you to test the voltage on pin 2 of the power tubes socket.
Output tubes removed.
Set meter for DC volts, 600. See where the V --- has a flat line?
Connect black probe to metal chassis.
Connect red probe to pin 2 of the output tube socket (or hold the probe so that the tip sticks down in the hole).
You can do this from the outside of the chassis (from the tube side). You don't need to do this from the inside.
Turn the power on just for a few moments.
Now we should see - 10 volts DC on pin 2 of the socket. Check both output tube sockets.
Turn power off.
Click to expand...
Hi @Amp Mad Scientist
Plugged the red on multimeter's DC V 600.
Plugged the black on COM (Max 600v)
Removed all tubes and followed your instructions.
Yes, all tubes removed, shows 10V on both power tubes'sockets.
 
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STRefugee said:
Hi @Amp Mad Scientist
Plugged the red on multimeter's DC V 600.
Plugged the black on COM (Max 600v)
Removed the 2 power tubes and followed your instructions. Multimeter shows 0.
Just for the hell of it I tested pin 3 and that showed around 355V on the multimeter.
Click to expand...
You tested pin 3 on both tubes?
You tested pin 2 on both tubes?

Can you test both legs of R31 and R32? (red probe on one leg at a time)
See if you are getting negative voltage at those 2 resistors?
bias test R31 R32.png
 
Sorry for confusing matters.
I just edited my message.
I had first done the test with the 3 smaller tubes still plugged in their sockets. Once all tubes removed, testing the 2 power tubes sockets on pin 2, both show 10V as expected.
 
STRefugee said:
Sorry for confusing matters.
I just edited my message.
I had first done the test with the 3 smaller tubes still plugged in their sockets. Once all tubes removed, testing the 2 power tubes sockets on pin 2, both show 10V as expected.
Click to expand...
OK that's what we wanted to see.
Pin 2 has the negative voltage and pin 3 has the high voltage, on both sockets.
So it's up to you if you want to change the board but so far haven't found anything wrong with it.
If the pads are actually lifting off the board you might want to change it, but discoloration from heat is normal and it will still work OK.
 
Amp Mad Scientist said:
OK that's what we wanted to see.
Pin 2 has the negative voltage and pin 3 has the high voltage, on both sockets.
So it's up to you if you want to change the board but so far haven't found anything wrong with it.
If the pads are actually lifting off the board you might want to change it, but discoloration from heat is normal and it will still work OK.
Click to expand...
I think you're right. The board seems fine.
 
Had a go and got a reading of 364v on pin 3 for both output tubes sockets.
Oh! Just realised i forgot to set it on AC.
Ok, just done that now but a reading of zero on pin 4 or 5 for both output sockets.
 
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STRefugee said:
Had a go and got a reading of 364v on pin 3 for both output tubes sockets.
Oh! Just realised i forgot to set it on AC.
Ok, just done that now but a reading of zero on pin 4 or 5 for both output sockets.
Click to expand...
Does the pilot light turn on when the power is on?

What happens when you put black probe on pin 4 and red probe on pin 5 at the same time?
Should see 6 volts AC there.

Black probe plugged into COM on the meter
Switch set to V "S" you see the sideways "S" on the meter switch? That's AC.
Set the switch to "200."

meter.png

Fender BLJR filament.png
The diagram specifies 120Volt wiring but the filament voltage remains the same for 230V power sorry didn't have a UK schematic.
Did you install the 5 amp fuse back into the amplifier?
 
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Amp Mad Scientist said:
Does the pilot light turn on when the power is on?

What happens when you put black probe on pin 4 and red probe on pin 5 at the same time?
Should see 6 volts AC there.

Black probe plugged into COM on the meter
Switch set to V "S" you see the sideways "S" on the meter switch? That's AC.
Set the switch to "200."

View attachment 105344
Click to expand...
Hi @Amp Mad Scientist,
Many thanks for taking the time to reply with added instructions, much appreciated!

Yes pilot red light is on.
Yes, i have done exactly as you instruct. I get no reading.
Even repeating the tests done yesterday i get nothing.
Only when testing pin3 do I get some voltage readings now.
 
STRefugee said:
Hi @Amp Mad Scientist,
Many thanks for taking the time to reply with added instructions, much appreciated!

Yes pilot red light is on.
Yes, i have done exactly as you instruct. I get no reading.
Even repeating the tests done yesterday i get nothing.
Only when testing pin3 do I get some voltage readings now.
Click to expand...
Did you put the 5A fuse back in?
Read post 109 again I added some things to it.
 
Amp Mad Scientist said:
Did you put the 5A fuse back in?
Read post 109 again I added some things to it.
Click to expand...
Yes it's been back in, still is.
I'll have another go tomorrow, in case I wasn't properly awake today.
Had next to no sleep over the last 48hrs so that might have affected me in some weird way.
But I can't think of what I may have done wrong.
 
STRefugee said:
Yes it's been back in, still is.
I'll have another go tomorrow, in case I wasn't properly awake today.
Had next to no sleep over the last 48hrs so that might have affected me in some weird way.
But I can't think of what I may have done wrong.
Click to expand...
You didn't do anything wrong probably.
The probes are not making good contact on the solder joints / the joints are oxidized.
Try rubbing an eraser on the solder joints to clean the metal, clean the end of your probes with the eraser.
The eraser works good to clean the oxide off of the metal.
1741378739239.png
 
Amp Mad Scientist said:
You didn't do anything wrong probably.
The probes are not making good contact on the solder joints / the joints are oxidized.
Try rubbing an eraser on the solder joints to clean the metal, clean the end of your probes with the eraser.
The eraser works good to clean the oxide off of the metal.
View attachment 105351
Click to expand...
Many thanks again!
Will try that and let you know how I get on.
 
STRefugee said:
Hi @Amp Mad Scientist
Today repeated the AC test on pin 4 & 5 on both output tube sockets.
Got a reading of 3.3 on both pin 4 & 5 on both tube sockets.
Thank you
Click to expand...
OK now test with power disconnected from amp.
set meter for ohms, 200.
connect black probe to metal chassis, connect red probe to pin 3 of output tube socket.
should read zero ohms for both sockets, or close to zero.
 
Amp Mad Scientist said:
OK now test with power disconnected from amp.
set meter for ohms, 200.
connect black probe to metal chassis, connect red probe to pin 3 of output tube socket.
should read zero ohms for both sockets, or close to zero.
Click to expand...
Hi @Amp Mad Scientist
Haven't got around doing it yet. To much going on atmo. But will find a moment to do it and get back to you btw today and tomorrow.

Thank you!
 
Amp Mad Scientist said:
I think that's the last test before you order parts. Everything was OK.
Click to expand...
Hi @Amp Mad Scientist
Have done the test
set meter for ohms, 200.
black probe to metal chassis, red probe to pin 3 of output tube socket.
got no reading. digital display showing: OL. that is what the multimeter shows when turned on as well.

turned the amp on a few secs.
tested voltage and that showed the reading as expected.
Then repeated the ohms test and still no reading. I assume that means Zero?
 
STRefugee said:
Hi @Amp Mad Scientist
Have done the test
set meter for ohms, 200.
black probe to metal chassis, red probe to pin 3 of output tube socket.
got no reading. digital display showing: OL. that is what the multimeter shows when turned on as well.

turned the amp on a few secs.
tested voltage and that showed the reading as expected.
Then repeated the ohms test and still no reading. I assume that means Zero?
Click to expand...
Turn the meter to ohms 200.
Touch the red and black probes together.
Should read zero or close to it.
Does it still read OL?
OL means open load, the ohms isn't working maybe.
 
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