I have a yamaha amplifier that has problems with the relays engaging. Tested the relays and they are working (engaging with a power supply). Also keep in mind the relay was bypass with a couple of jumpers but this is causing a turn on thump and it is annoying, especially knowing how well the relay delay method works (have another YPA-100 without issues and the relay works perfectly). I already removed the jumpers, want to make the relays engage work properly.
The amplifier is very similar to the YPA-720 so am using those schematics and they are identical. It uses a uPC1237HA IC as the driver for the relays.
These are the voltages I got from 1237HA:
1) 1.97 (should be 0)
2) 0
3) 0
4) 0 (should be 5-6v)
5) 0
6) 22.4 (should be 0.6)
7) 0.045 (should be 2.1)
8) 3.3
TR605
E) 22.4
C) 22.4 (should be 0 as it is tied to pin 1 of 1237HA in series with a 10k resistor)
B) 6.85 (should be 22.4 and is tied to each ch's TR604 transistor's collector pin).
Now while I was testing and measuring several transistors in the circuit of the relay driver, the relay engaged (clicked) and audio was present this was after a good 20 minutes of the amplifier being in idle. However powering the amplifier off then turning back on causes the same "no audio" issue due to the relays not engaging.
Am thinking the problem is in each ch's TR604 transistor as it's in circuit with the "Overload" pin of 1237HA.
The amplifier is very similar to the YPA-720 so am using those schematics and they are identical. It uses a uPC1237HA IC as the driver for the relays.
These are the voltages I got from 1237HA:
1) 1.97 (should be 0)
2) 0
3) 0
4) 0 (should be 5-6v)
5) 0
6) 22.4 (should be 0.6)
7) 0.045 (should be 2.1)
8) 3.3
TR605
E) 22.4
C) 22.4 (should be 0 as it is tied to pin 1 of 1237HA in series with a 10k resistor)
B) 6.85 (should be 22.4 and is tied to each ch's TR604 transistor's collector pin).
Now while I was testing and measuring several transistors in the circuit of the relay driver, the relay engaged (clicked) and audio was present this was after a good 20 minutes of the amplifier being in idle. However powering the amplifier off then turning back on causes the same "no audio" issue due to the relays not engaging.
Am thinking the problem is in each ch's TR604 transistor as it's in circuit with the "Overload" pin of 1237HA.
Also once audio was present I check voltages of the 1237HA and the voltages matched the schematics, what I have in parentheses as "should be".
YES it did work Perry, you are the man. There's about a 2 second delay which is just enough to avoid the turn on thump/pop.
Perry PLEASE tell me how you figure this out, I don't want answers handed to me rather an explanation why it fail or not working as it should. I don't know why I didn't bother to remove it when I spent over an hour just messing in that area around the transistor.
If that transistor failed, I found a replacement for it or is it safe for the amplifier to run without the TR605? No protection?
Perry PLEASE tell me how you figure this out, I don't want answers handed to me rather an explanation why it fail or not working as it should. I don't know why I didn't bother to remove it when I spent over an hour just messing in that area around the transistor.
If that transistor failed, I found a replacement for it or is it safe for the amplifier to run without the TR605? No protection?
Last edited:
I didn't figure anything out. Removing that transistor disconnected the protection circuit transistors from the protection IC.
I agree that having a Vbe of greater than 0.7v is a problem. TR605 may well be defective. It's not a critical component. Virtually any PNP transistor with the correct pin configuration could be used as a (temporary) replacement.
After you get a known-good transistor in that location, if the amp still malfunctions, remove one TR604 at a time to see if one channel is causing the amp to go into protect mode.
If you find one channel that's causing the problem, you'll troubleshoot from there.
It's not safe to operate the amp (for more than testing) without that transistor.
I agree that having a Vbe of greater than 0.7v is a problem. TR605 may well be defective. It's not a critical component. Virtually any PNP transistor with the correct pin configuration could be used as a (temporary) replacement.
After you get a known-good transistor in that location, if the amp still malfunctions, remove one TR604 at a time to see if one channel is causing the amp to go into protect mode.
If you find one channel that's causing the problem, you'll troubleshoot from there.
It's not safe to operate the amp (for more than testing) without that transistor.
Hey Perry I found a 2sc3402 on TR607 (which in the schematic is label as a 2sa1318)...if the schematics are correct then this is most likely the issue, error at the factory.
EDIT: DISREGARD what I wrote on top. Found on the circuit on this amp is a bit different than the 720. This one has a NPN tied to the TR605 (2sc3402) I'll post a picture of the diagram to show where it's located and what pins it's tied to.
I went ahead and purchased the service manual for the 700, was getting a bit confused as this one has an extra component and are not label the same. So to avoid confusion I went ahead and got the correct schematic.
The component dedication numbers (TR###) don't exactly match my board but they are exactly the same lay out. For example on the schematic's TR819, it's actually 607 on the board. But they are the same component. Hope this doesn't cause confusion.
Perry let me know if you want a pdf copy, I'll email it to ya.
The component dedication numbers (TR###) don't exactly match my board but they are exactly the same lay out. For example on the schematic's TR819, it's actually 607 on the board. But they are the same component. Hope this doesn't cause confusion.
Perry let me know if you want a pdf copy, I'll email it to ya.
Attachments
Last edited:
Isn't the troubleshooting procedure the same (removing TR604s to see if one channel is at fault?
The extra transistor seems to be there to discharge a capacitor.
The extra transistor seems to be there to discharge a capacitor.
Yes.... I'll be doing that later tonight.
Question: If the relay was bypassed with jumpers (so signal still goes through, without relay's been engaged) wouldn't this be like bypassing the protection circuit (TR605)?
Question: If the relay was bypassed with jumpers (so signal still goes through, without relay's been engaged) wouldn't this be like bypassing the protection circuit (TR605)?
It would effectively take the protection circuit out of the circuit. You don't want to operate the amp without the protection circuit.
Okay the issue is in ch 1 (prefix a).... Removed 604a and the amplifier's relay engage as normal.
If it appears OK, you can swap it with 604B to confirm that it was that transistor.
If any transistor in 604a causes it to remain in protect, look at the emitter resistor solder connections. If they're OK, remove the resistors and check them out of the circuit.
If any transistor in 604a causes it to remain in protect, look at the emitter resistor solder connections. If they're OK, remove the resistors and check them out of the circuit.
- Status
- Not open for further replies.