Harman Kardon hk570i dead channel help

[SpiritCat]

Not sure any difference, but corrected to one pin goind to Right speaker out.

 

[Dave1027]

<deleted>

 

[SpiritCat]

Those green wires off the transformer are not full 120V AC, and at the posts on the rectifier board read 7.28V AC (green/orange post) and 6.48V AC (green post). Thus, are you referring to removing those little ceramic disc capacitors also attached to those green wire posts? Or are you referring to a potential issue with the capacitor on the switch and/or the resistor off the rear recepticle and to ground (red circles on attached)? I do wonder if this reciever should be converted to a 3 way grounded AC main plug supply, although I would have to research how. Could that Resistor on the lead to ground fail and let full AC hot to chassis? The red and white transformer supply wires are buried within the transformer on its top, but I can access them/full voltage under the transformer.

 

[Dave1027]

Disregard my concern about the caps. It looked like in your pic that the green wires were connected to the primary. My mistake. Also adding to the confusion is your wiring diagram shows a different transformer than the diagram I was looking at.

There is no real need to convert to a 3-wire grounded power cord.

 

[SpiritCat]

Thanks for response. I did a little research and concluded the same, that I do not need to convert to 3-prong and that doing so might result in other issues, like noise or ground loops. I have neither of those issues now. Comparing to other schematics and documents I have studied while I am attempting to learn from others troubleshooting, I conclude that the technical information for this unit is shoddy work.

I think the only thing left for me to do to get this unit fully restored is to figure out why/how I lost FM reception/tuning. I did take measurements off the pins on IC 301 and several are not right, do not match the schematic. My plan will be to path trace from those pins and possibly pull some parts to test. Hopefully, my ICs are not the problem because I don't think they are readily available.

 

[SpiritCat]

Troubleshooting AM/FM, all of the connections from the dipole FM antenna are connected together and even to chassis (ground). Is this correct? Could this be why I am no longer recieving reception and LEDs are all lit as though I am?

 

[SpiritCat]

I have spent hours figuring out how AM/FM works, marking up the schematic to label all the component functions and eventually landed on focusing on the FM IF Integrated circuit HA11225 chip which had all wrong (too high) voltage readings except for the 14v rail input pin. Diagnosing this issue, I focused on some parts around the chip and even changed some transistors. Then I discovered the 2 ground pins were only connected to chassis and not the transformer ground post. While tracing the ground, I found a tiny gap in a copper trace (picture attached after I scratched for a jumper fix). Now, all the LED lights have gone off and I get AM static with station strength trying to tune, but I don't expect AM to come in where I am located. The FM is still silent, no static or any change to LED station strength lights. I may change back to original transistors to see if this fixes the problem. I don't understand FM alignment nor think I have the tools to do this, so I am hoping that going back to original parts will get me back to original alignment/ working again.

 

[SpiritCat]

HK 460i is all fixed! I was able to determine the HA11225 chip was no good. I found one on Ebay, new old stock and after installing, all works well again from the tuner board. Attached is a photo of the unit ready to be put back into its case. I may change the old display bulbs to LED since I broke one on the left side and believe its impossible to find another like it. Attached shows my schematic markup that helped me understand what I was looking at. In the end, I probably caused some of the issues I encountered myself. Big lesson I learned, if you see erratic voltages, check all grounding before swapping parts. And connect ground to transformer, not chassis . In the end, I bought a bunch of parts (transistors, resistors, diodes, and capacitors, and more) and barely used any of them. Now, on to refurbishing my 1980s Dual 606 turntable.