Hey folks, I've come here because it looks like this group has helped a lot of people get Harmon Kardon AVR's back up and running.
My AVR3700 had it's standby power supply blow out a few weeks ago. I have been trying to get it back up and running, but am pretty much striking out on everything I have tried. My background is just hobby level stuff, mostly dealing with analog electronics. I do a lot of work on car audio amps, but this is my first mains powered receiver that I have attempted to fix. The SMPS's in this receiver are quite a bit more complex compared to what I am used to.
Below is a list of failed components that have been replaced:
1) IC91- this is the standby supply SMPS driver, OB2358L, the original had the top of the case blown clean off.
2) D914- MM1Z18, 18V zener on the supply side of the SMPS driver, looks to be there to clamp input voltage during a fault.
3) D928- 20V zener, again, appears to be protection during fault condition.
4) R928,967,972,970,971- These are current sense resistors for the driver. All were toasted, reading 1+ Meg, supposed to be 10 ohms
5)D901/902- supply primary side of TF91, the standby transformer.
I have checked every other cap, resistor, diode, transistor, opto-coupler, and the voltage regulators in the standby supply. They all test fine. The new OB2358L tries to start, but it never manages to take off, it resets and tries to start again and again.
I'm close to my wits end with this thing. I am pretty stubborn when it comes to troubleshooting and repair, but I simply cannot figure out what is keeping this supply from working. Yesterday I decided to lift the cathode on D943 and D921 to see if there was a short somewhere downstream of the xformer. The supply still won't start. I did not really expect it to as D921 breaks the feedback loop, but I started with just D943 lifted and still no pulses. As a last ditch effort I pulled the standby transformer. I couldn't come up with a great way to test it, so I tried to use stepped down mains voltage to drive it. Transformer and leads got very hot and then blew a 2 amp fuse. No AC on the secondary side while I could test. The problem is, this transformer is probably designed for 50+ kHz and 60 Hz may have just saturated the core. By process of elimination I am thinking it is the xformer that is bad, but I don't know if parts are available, and I am also not 100% sure that I did not miss something else while troubleshooting.
If anyone has any thoughts, please LMK. I'll try to attach the PDF of the SMPS in question, I have the full service manual hosted here, on my website.
I apologize for the long post, but I wanted to try to be thorough explaining what I have checked so we would not have to reinvent the wheel...
Thanks,
Jason
My AVR3700 had it's standby power supply blow out a few weeks ago. I have been trying to get it back up and running, but am pretty much striking out on everything I have tried. My background is just hobby level stuff, mostly dealing with analog electronics. I do a lot of work on car audio amps, but this is my first mains powered receiver that I have attempted to fix. The SMPS's in this receiver are quite a bit more complex compared to what I am used to.
Below is a list of failed components that have been replaced:
1) IC91- this is the standby supply SMPS driver, OB2358L, the original had the top of the case blown clean off.
2) D914- MM1Z18, 18V zener on the supply side of the SMPS driver, looks to be there to clamp input voltage during a fault.
3) D928- 20V zener, again, appears to be protection during fault condition.
4) R928,967,972,970,971- These are current sense resistors for the driver. All were toasted, reading 1+ Meg, supposed to be 10 ohms
5)D901/902- supply primary side of TF91, the standby transformer.
I have checked every other cap, resistor, diode, transistor, opto-coupler, and the voltage regulators in the standby supply. They all test fine. The new OB2358L tries to start, but it never manages to take off, it resets and tries to start again and again.
I'm close to my wits end with this thing. I am pretty stubborn when it comes to troubleshooting and repair, but I simply cannot figure out what is keeping this supply from working. Yesterday I decided to lift the cathode on D943 and D921 to see if there was a short somewhere downstream of the xformer. The supply still won't start. I did not really expect it to as D921 breaks the feedback loop, but I started with just D943 lifted and still no pulses. As a last ditch effort I pulled the standby transformer. I couldn't come up with a great way to test it, so I tried to use stepped down mains voltage to drive it. Transformer and leads got very hot and then blew a 2 amp fuse. No AC on the secondary side while I could test. The problem is, this transformer is probably designed for 50+ kHz and 60 Hz may have just saturated the core. By process of elimination I am thinking it is the xformer that is bad, but I don't know if parts are available, and I am also not 100% sure that I did not miss something else while troubleshooting.
If anyone has any thoughts, please LMK. I'll try to attach the PDF of the SMPS in question, I have the full service manual hosted here, on my website.
I apologize for the long post, but I wanted to try to be thorough explaining what I have checked so we would not have to reinvent the wheel...
Thanks,
Jason
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