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I could use some additional help with the amp, unfortunately after a few days of listening, I noticed a problem with the right channel, it still worked, but there was a fairly loud DC related pop when the amp was powered off and on. After further investigation, it turns out that the right...

After examining as many pictures of the HK6900 as I could find online, I noticed that most all of them have the same modification to the protection circuit, so it must have been an undocumented production change to the amp. It consists of a 680Kohm resistor between the power rail of the driver...

Thanks Ray, based on my amateur detective work I'm going to err on the side of trusting the service manual. It's been 100% accurate so far except for that group of fusible resistors and I can tell that they have been replaced at some point since the leads are not bent over the solder pads as...

Thanks, I appreciate the encouragement and good luck with the PM650!

I recently purchased a non-functional Harman Kardon HK6900 integrated amp. After some initial troubleshooting, I found that it has extremely high DC offset in the right channel and highish DC offset in the left. Strangely, the amp came out of protection without issue. I continued digging...

Thanks to everyone for responding, very informative.

Thanks to everyone for the advice. Any idea why Sony would choose to put a 330 ohm resistor (R202) in series with the 330pF (C201) cap? I've not seen this in other phono pre schematics, typically it's just the loading capacitor and loading resistor in parallel to the input. To...

I have a Sony TA-F707ES integrated amp and am considering purchasing a new Audio Technica MM cartridge for my turntable. Although it is not listed in the specs for the amp, by looking at the schematic it looks like there are 330pf polystyrene caps in parallel with the phono stage inputs. Am...

Sure, here is the link.

Thanks, I appreciate your efforts too, hopefully this will help keep these wonderful turntables out of the landfill. I made some progress today but am still dialing in the gain and offset. The trouble that I am having is that the PS-X50 manual states that the gain should be set to 1.9V AC...

Ok thanks, when I got the table it was wildly out of spec, with almost no gain on one of the elements and the gain adjustment pot pegged at max for the other and wonky speed issues. After about an hour of fiddling, the voltages are relatively close to balanced as far as I can tell on my scope...

No offense taken, I am always willing to learn and appreciate advice and guidance. As far as trigger level, yes, I have attempted to adjust but it makes no difference at with current horizontal timebase of .2 seconds (video can be found here). If I move the horizontal timebase to .5-1 ms I get...

Thanks for getting back to me, I'm measuring the Hall Device Gain and Motor Amp Offset (SM pictures attached), using an analog scope for both since I don't have a VTVM. I have a regulated DC power supply hooked up and providing 1.5V and am attempting to measure 1.9V peak to peak for the gain...

I have a Sony PS-X50, I'm working through the gain and offset procedures. I have an analog scope (and a DMM that doesn't seem to be of much use) but am finding that the sweep speed is so slow that I'm not getting persistent waveform to measure. Instead, the waveform looks like a fast bouncing...

After more parts replacement and adjustment the TT71 is working great, the quartz lock is working and the motor running silently after a thorough cleaning and lubrication. I used my iPhone RPM app and it's measuring .06% wrms wow, so pretty close to the factory spec of .045%, not bad for a 45...

Making progress, for some reason the previous owner replaced nearly every transistor, diode, ceramic cap and oddly put in an opamp socket for IC801, the replacement transistors were wildly incorrect as were some of the other parts. Since exact replacements for the original transistors aren't...

I recently bought a JVC QL-7, after getting it home, it turns out that the speed is inconsistent and the quartz lock doesn't seem to be engaging. I downloaded the service manual thinking I would go through the alignment/adjustment procedures but to my unpleasant surprise found some poorly...

Thanks, I ended up buying some for a 1" tweeter from an eBay seller who specializes in speaker repair, seems to work great so far!

I'm replacing a badly dented tweeter on my B&W CDM 1NT speakers. The replacement tweeter is brand new, but the tweeter in the other speaker is 20+ years old and could use some new ferrofluid. It seems like there are a lot of options out there for ferrofluid, can anyone recommend the correct...

I recently picked up a Proton 930 receiver at the thrift store with the intention of using it in my workshop. In disassembling it for cleaning, I was surprised at just how well designed this thing is. In addition to a serious tuner it has a very nice, fully discrete phono preamp that takes up...

A little bit stripped, right? To Johnstigator's observation I don't think that there is any white heatsink compound, just an irregularity in the mica. I plan to clean and regrease the transistors and can confirm though. Given the potential mismatch, is there anything to be gained by replacing...

I have a Marantz 2245 that I've owned for about 10 years and have used off and on. I brought it out for checkup recently and upon inspection, it seems that one of the PNP output transistors is different from the others. I've never seen one quite like it, it almost looks like the original...

The kit provided by speaker-terminal.com is a direct replacement. If you have basic soldering skills it should be very easy to do as it is as simple as de-soldering the speaker wires, unscrewing the old terminals, replacing with the new terminals, and soldering the speaker wires to the new...

Well that's all I have, it's been fun project and I hope that my notes can help anyone else who has a PM-94. This amp (along with my PA-7) is the pride of my collection and I hope to have it for a very long time. While I'm happy with how the amp turned out I'm on the fence as to whether I...

A few final pics, I'm far from an expert woodworker but I was able to knock together a pair of replacement side panels with maple planks and shellac. It gives the amp a clean, modern look and they are certainly better than the original panels which look like they lost a fight with a grizzly...