Nice video, thanks for posting it. Once you've redone soldering on the tone board and the issue was still there my guess was that perhaps it's with wiring connections. But apparently it was something different. Good you were able to spot it out and have it fixed!
At 18:00 the phase difference tells me the loudness switch isn't fully disengaged on one channel. This is confirmed shortly after when you demonstrate the effect goes away at higher volume. With a square wave input you could see the difference instantly, and see the problem go away when you fiddle with the Loudness switch. So far as the original problem, I haven't got to the end of the video as I write, but the pre-main jacks have built in switches which are notorious for causing your level imbalance. Just hose down an RCA plug with De-Oxit and insert into the pre-main jacks and rotate several times, or your can just jumper with RCA cables. The loudness and other switches CAN be cleaned without dis-assembly.
That's great insight re: the loudness switch. If you watched to the end, you already know that I found the need to clean the loudness switch. I didn't know what to make of the phase difference or the disappearance of the problem with increasing volume, but your assessment makes perfect sense. There is some remaining imbalance that increases with volume. Could the pre-main jacks and switches cause that? I don't expect I've opened that case for the last time ... To clean the front panel switches, does it work to squirt DeoxIT into the front? The fit is pretty tight, but I can imagine that enough might get in, especially if you tilted the front up. Gravity assist.
@@Lancaster_Hi-Fi It's certainly worth a try cleaning the pre-main pin-switches (I call them) or as I say jumper them with RCA cables. To clean the loudness, tape monitor etc switches it's a little hard to explain but here goes: The knobs and front panel must be removed. Have De-Oxit or other cleaner with extender straw ready. Arrange to pull the receiver upright with the front panel pointing up to the ceiling. This is to get gravity working in your favor. I use parts boxes or towels to protect the rear panel . You'll need to be careful not to let the receiver tip over. Spray De-Oxit down each side of the switch shaft so it runs down inside the switch, and work the switch many times. It's a good idea to repeat this, an even better idea to repeat after 24 hours. All the switches that affect signal should get this treatment. Some other brands have small holes in similar switches you can use to spray in. By the way some other models this technique doesn't work, like the Harman Kardon 330, 630 etc. The silver content makes them tarnish badly inside. The switches must be replaced or dis-assembled for service. You'll notice there was no tarnish inside yours.
@@Lancaster_Hi-Fi I've only worked on maybe one HK 670, don't recall their switches being a particular problem. The FM would just need troubleshooting, but I always start with power supplies.
I want to thank you again for your careful instructions on how to treat these switches. I have now used the technique on other units to good effect. Specifically, I had a Nikko TRM-750 that was driving me mad with intermittent noise that I couldn't track down. I finally solved the problem completely with your DeoxIT-with-the-unit-on-its-back method.
Nice video, thanks for posting it. Once you've redone soldering on the tone board and the issue was still there my guess was that perhaps it's with wiring connections. But apparently it was something different. Good you were able to spot it out and have it fixed!
At 18:00 the phase difference tells me the loudness switch isn't fully disengaged on one channel. This is confirmed shortly after when you demonstrate the effect goes away at higher volume. With a square wave input you could see the difference instantly, and see the problem go away when you fiddle with the Loudness switch.
So far as the original problem, I haven't got to the end of the video as I write, but the pre-main jacks have built in switches which are notorious for causing your level imbalance. Just hose down an RCA plug with De-Oxit and insert into the pre-main jacks and rotate several times, or your can just jumper with RCA cables. The loudness and other switches CAN be cleaned without dis-assembly.
That's great insight re: the loudness switch. If you watched to the end, you already know that I found the need to clean the loudness switch. I didn't know what to make of the phase difference or the disappearance of the problem with increasing volume, but your assessment makes perfect sense. There is some remaining imbalance that increases with volume. Could the pre-main jacks and switches cause that? I don't expect I've opened that case for the last time ...
To clean the front panel switches, does it work to squirt DeoxIT into the front? The fit is pretty tight, but I can imagine that enough might get in, especially if you tilted the front up. Gravity assist.
@@Lancaster_Hi-Fi It's certainly worth a try cleaning the pre-main pin-switches (I call them) or as I say jumper them with RCA cables.
To clean the loudness, tape monitor etc switches it's a little hard to explain but here goes:
The knobs and front panel must be removed. Have De-Oxit or other cleaner with extender straw ready. Arrange to pull the receiver upright with the front panel pointing up to the ceiling.
This is to get gravity working in your favor. I use parts boxes or towels to protect the rear panel .
You'll need to be careful not to let the receiver tip over. Spray De-Oxit down each side of the switch shaft so it runs down inside the switch, and work the switch many times.
It's a good idea to repeat this, an even better idea to repeat after 24 hours. All the switches that affect signal should get this treatment. Some other brands have small holes in similar switches you can use to spray in. By the way some other models this technique doesn't work, like the Harman Kardon 330, 630 etc. The silver content makes them tarnish badly inside. The switches must be replaced or dis-assembled for service. You'll notice there was no tarnish inside yours.
Thanks! That's really helpful. And about the HKs, what about the later models, like the 670? I have one of those with an FM problem.
@@Lancaster_Hi-Fi I've only worked on maybe one HK 670, don't recall their switches being a particular problem. The FM would just need troubleshooting, but I always start with power supplies.
I want to thank you again for your careful instructions on how to treat these switches. I have now used the technique on other units to good effect. Specifically, I had a Nikko TRM-750 that was driving me mad with intermittent noise that I couldn't track down. I finally solved the problem completely with your DeoxIT-with-the-unit-on-its-back method.
Where did you learn your trade sir?
I took an electronics class in college, but that was a long time ago, so I've just learned what I needed to know.