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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...

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...

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...

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...

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...

I was test-fitting a brand new, out of the bag 20,000uf 100v filter capacitor for the amp project that I am working on. Much to my surprise, it dead shorted with a spark on one of the loose ring terminals, which is in turn connected to the bridge rectifier. It wasn't a large spark, and it...

Thought I'd show off my new PM-94, I have always wanted one and couldn't resist when one popped up on eBay for a reasonable price. One of the wood side panels is missing a chunk and one of the speaker terminals has snapped off, but otherwise it is in good condition. I was able to dial in the...

I have a treasured pair of KEF 103.2 speakers that are starting to sound a little tired lately, I'd like to replace the crossover capacitors to help restore the sound but I am finding that exact replacements are hard to come by. I love the sound of the speakers and am leery of changing the...

A few months ago I bought a Nakamichi PA-7. It was in pretty rough but functional condition. After some maintenance, it sounds much better and works as designed with one small issue... As the power button is pushed, a relatively small transient pop can be heard through the speakers. This is...

I recently bought a Nakamichi PA-7 amplifier and removed the heatsinks do to a little maintenance. To my surprise, I found two Yamaha decals on the inside of one of the heatsinks, I suppose it could also be remnants of shrinkwrap that was never fully removed. Does anyone know if Yamaha built...

I recently picked up a PM660 integrated amp after reading quite a few positive review and being intrigued by the (partial) dual mono, low feedback design. It has a fully discrete phono preamp that supposedly sounds great. While cosmetically very good, this amp is a bit of a basket case...

Hi, I'm tuning up a MCS 3845 for a friend, I'm having a hard time finding a service manual for it, does anyone have one to share? It seems superficially similar to the NEC AUA-7000e, which I did find a SM for, but the NEC has discrete output devices whereas the 3845 has STK power modules. If...

I recently picked up a Sony TA-F707ES integrated amp from the early 90's. It works, but is extremely dirty. I've disassembled it for cleaning and am planning to replace the circuit board electrolytic caps while I have it apart. I'm wondering if it is necessary to replace the large filter...

Just picked up a used Onkyo A-9070, I'm mostly a vintage guy but this was too good of a deal to pass up. There doesn't seem to be much info on these amps online, and they aren't common in the US, so thought I'd post some pictures and impressions. Luckily I was able to find a copy of the service...

I recently picked up a C-85 preamp that is somewhat worse for the wear cosmetically and electrically, but worth saving. The preamp works, but it has some very rough looking capacitors and transistors. I'm putting together a shopping list and having trouble with the 4 4700uf 35v power supply...

The power switch on my AX-700 is acting up, if I turn it on and release the button the connection is flaky and intermittent, the amp powers on and off constantly in quick succession. If I turn it on and hold the button it powers up normally and I get a relay click. I've given the switch a...

Did a tuneup of my workhorse CA-810 amp and decided to use it to practice my oscilloscope technique. I've been reading up on how to use an oscilloscope for audio diagnostics and for my first test decided to measure power output. The scope that I have is an old Goldstar unit that I picked up...

I'm hoping I didn't damage my brand new Project phono preamp, I touched the top of my amplifier and received an almighty static shock, my finger is still smarting from it. My phono preamp immediately powered off, I am guessing this is by design, but a little paranoid that I may have damaged it...

A while back I finally got my hands on a CR-2040, which has been a "holy grail" since I got into hifi 6 or so years ago. Supposedly the CR-2040 sounds great, and in my opinion it is the best looking receiver ever made. The example that I have is in fair shape, the case is beat up but it mostly...

I recently purchased a Denon DP-755 turntable with a Pioneer PA-1000 tonearm. Unfortunately, the tonearm is missing the anti-skate weight. It is a donut shaped weight that clamps on to a graduated rod. Is there anyone who has this tonearm who could weigh this weight for me? This would help in...

A while back I bought a Yamaha YP-D6 DD turntable. Unfortunately it wasn't packed well and the motor mounting cup and spindle were bent during shipping. I bought a replacement cup, motor, and spindle and am finally ready to get this thing spinning vinyl once again. The motor has 15 wires...

I recently picked up a very nice pair of KEF 103.2 speakers, they sound amazing but I'd like to swap out the end tables that they have been sitting on for actual speaker stands. Any recommendations? I'd like to keep the price under $100 if possible, these Monoprice speaker stands seem like a...

I picked up a non-functioning CR-2020, it looked great outside but ended up being somewhat of a basket case inside, likely due to heavy use. The main filter cap board had a number of traces that had been roasted off of the PCB and some not so happy caps, transistors and resistors. I replaced...

I'm considering buying an MC phono cartridge and would like to know if it is possible to update the MC phono stage in my CR-2020 to support 100 ohm loading for modern MC cartridges. Per the service manual, it is 10 ohms from the factory. I've been staring at the schematic and am struggling to...