What you see on both pictures is the component side. The other side is the solder side and as I said, you will have a though time to take that PCB out. Try the tapping trick, (gently) and measure some more DC values.
If you feel uncomfortable taking the amp apart, consider a service center.
/Hugo
If you feel uncomfortable taking the amp apart, consider a service center.
/Hugo
For some reason I still think the amp is working and somewhere along the line something very simple is wrong, like a jack input or so.
If you proceed, you will need to measure the VAC voltages.
On the schematic, you can find the conditions to measure them under Notes-> point 7
You will need a sinewave generator.
The resistive load can be a speaker but better is to use a 8 ohm power resistor.
/Hugo
If you proceed, you will need to measure the VAC voltages.
On the schematic, you can find the conditions to measure them under Notes-> point 7
You will need a sinewave generator.
The resistive load can be a speaker but better is to use a 8 ohm power resistor.
/Hugo
What I haven't heard here yet is us isolating the problem. have we connected the amp to a different speaker? Have we verified the speaker cord is OK? Is the speaker connected to the right jack?
I doubt the tube is involved. I think the amp works without the tube even in there. As far as I can tell, all the tube is used for is clipping.
If that is all OK, then divide and conquer. Plug the guitar into the effects return. Does it come out strong now? If not, the power amp and back half of the circuit is suspect. If sound is OK, then the power amp is good.
Connect the effects send to another amp so you can monitor what the preamp is sending out. If it is weak, then the power amp output will be weak too. If it is strong, then the preamp is OK.
Turn the reverb up and rock the amp a time or two to get reverb crash sounds. if that is lound, that also verifies the power amp as OK, suggesting the preamp is bad. If it is not loud, then the power amp is suspect.
If neither half of the amp works right, you want to look to power supplies or stages between the effects return and the power amp, like U4, U5.
This thing is a sea of op amps. Put a fingertip on each one. ANy getting hot? Bad sign if so. All those dual op amps have outputs on pins 1 and 7. Check them for signa.
Got a scope? Apply a signal to the amp input and see where ti disappears. No scope? Apply a relatively hot signal to the input - plug a CD [player into there if you have no signal generator. Use your meter set to AC to follow signal through the amp.
While there certainly are many times a problem is due to solder and other stuff, it makes sense to isolate the problem to a part of the amp. that makes it a lot easier to finish the repair.
Here is one quick thing to check though. Near the end of the heat sink is a large 10 watt resistor. 0.22 ohms R116. See if it is open, broken off at the leads, or unsoldered. it is the speaker return to ground electrically, and if it opens, you get little output.
I doubt the tube is involved. I think the amp works without the tube even in there. As far as I can tell, all the tube is used for is clipping.
If that is all OK, then divide and conquer. Plug the guitar into the effects return. Does it come out strong now? If not, the power amp and back half of the circuit is suspect. If sound is OK, then the power amp is good.
Connect the effects send to another amp so you can monitor what the preamp is sending out. If it is weak, then the power amp output will be weak too. If it is strong, then the preamp is OK.
Turn the reverb up and rock the amp a time or two to get reverb crash sounds. if that is lound, that also verifies the power amp as OK, suggesting the preamp is bad. If it is not loud, then the power amp is suspect.
If neither half of the amp works right, you want to look to power supplies or stages between the effects return and the power amp, like U4, U5.
This thing is a sea of op amps. Put a fingertip on each one. ANy getting hot? Bad sign if so. All those dual op amps have outputs on pins 1 and 7. Check them for signa.
Got a scope? Apply a signal to the amp input and see where ti disappears. No scope? Apply a relatively hot signal to the input - plug a CD [player into there if you have no signal generator. Use your meter set to AC to follow signal through the amp.
While there certainly are many times a problem is due to solder and other stuff, it makes sense to isolate the problem to a part of the amp. that makes it a lot easier to finish the repair.
Here is one quick thing to check though. Near the end of the heat sink is a large 10 watt resistor. 0.22 ohms R116. See if it is open, broken off at the leads, or unsoldered. it is the speaker return to ground electrically, and if it opens, you get little output.
roc pro
I would like to know if you solved your problem as I've encountered a similar situation. I eventually traced it to the nine pin jack socket contacts, replacing the jack solved it and the amp now sounds sweet.
Does anyone have the test points voltages etc. as these would come in very usefull.
I would like to know if you solved your problem as I've encountered a similar situation. I eventually traced it to the nine pin jack socket contacts, replacing the jack solved it and the amp now sounds sweet.
Does anyone have the test points voltages etc. as these would come in very usefull.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.