sx-780

I have an SX-780 that plays fine... mostly. After around 20 minutes of use, the volume of the right channel will instantly increase (by a lot) with treble-y distortion... for ONE SECOND. Then, back to normal. 1. It has been serviced and had STK-0050s replaced last year. 2. It went back to the...

Recently serviced and tech said all inputs functioned. It works fine on Phono and FM but it’s very quiet when using tape 1 or 2 and AUX. it does not seem to be driving the speakers properly. Sounds like just the tweeters maybe and the meters barely move). I’ve tried multiple input cables and...

I went through this 780 with a restoration kit I got off of eBay. I also installed the stk-0050 replacement power packs. Everything lowers up and sounds amazing. It drives my large ESS speakers very well. Amazing deep bass. It however will randomly go into protection mode. It doesn’t matter if...

After I brought a SX-780 home the relay would not engage at all. I've refreshed solder on Q25 and the relay started to engage and was getting FM working on the right channel and crazy loud whistling sound on the left. The whistling would start immediately after turning it on independent of the...

Hello all, a friend of mine dropped off a SX-780 that was in protection and ask if I could fix it for him. Having repaired/restored I think 3 of these before, I agreed. I powered up with the DBT and sure enough it had all the signs of a blown STK0050 module. I had a good spare and installed it...

I have this situation: Right now I have only one STK-0050 in, the other one is removed because it was bad. When I play some FM station in STEREO the sound is very low volume and intermittent. If I slowly turn the tuning knob the loud noise waves occur and then settle to the previos low volume...

Hello, I have a question about an sx-780 I want to fix up. A little background on me, I've done some tube radios, both AM and one AM/FM. I'm familiar with basic soldering/desoldering, recapping, and limited troubleshooting. Use (in series) an isolation transformer, variac, and dim bulb tester...

I am refurbishing a Pioneer SX-780. Two of the three sockets have one of the two plastic clip legs broken. I am currently holding them in place with 3m Glass Cloth tape but would really like to replace sockets. Has anyone found a socket that will work? I don't mind rewiring if it does not...

First post here so thanks in advance. I am a tube amp tech and have recently started learning some new things with my Pioneer SX-780. So I am have an issue that I so far cannot seem to find the problem. I bought a restore kit and have done all the work so far, still no love. I sure would...

So, I have an SX-780, which sounded terrific until the left side speaker bank developed distortion. Traced it to a failed STK, and decided to replace both STK in the short term with a replacements bought online. I WILL be purchasing, assembling and installing the much-better replacement...

Hi everybody, I am in the process of restoring a Pioneer SX-780 and would need some guidance from the gurus to get it to the finish line. The unit powers on and never blew fuses but had 1, possibly both STK's blown and protection relay would not click. This made sense as the voltages at the STK...

The unit powers up with all lights and movement on the tuner meter, but no movement whatsoever from the VU meters and no audible relay click. I’ve read several threads about how to test the relay not coming out of protection mode but I'm not sure where to go from here. I have diode tested the...

Good morning, fellow AKers. I've got a never-before-seen, unusual problem with about 13vdc in the left channel of the preamp section. This problem started out with a recently as-is purchased Pioneer SX-790 that would trip the protection relay whenever the volume control was moved up (or down)...

Hi Team, I have a Pioneer SX-780 that I've recently repaired. I replaced the Darlington Power Pack on the left channel which was previously shorted. After the R&R all seemed to be working correctly. Everything sounded great. In the process of testing out the unit I've been trying different...

Hello- New to the vintage receiver sx-780 test/repair arena. Acquired an sx-780 with a shorted Darlington STK0050. Was looking at the replacement stk0050 from this thread- and the parts list/ebay item...

Getting Neil Young "Hey,Hey, My,My" type distortion from left channel with volume set anything beyond three. But not getting any distortion through headphones at all. I seek wisdom from the AK masters....

Hello All, I acquired this sx-780, which had been abandoned in an office move in the 90's and put it in my garage as a retirement project, well that is here now. Yesterday I got it out, and powered up without speakers. Lights on, LED's work( tape monitor, Stereo), Tuning meter works. I...

Hi Gang - So I have a Pioneer SX-780. When I first got it a number of years ago it would power on, but no click. Did some research at the time and replaced the STK-0050 Packs (with what I'm sure were not the real thing, but impossible to find the real thing) and it's worked fine since then...

Hi all, I was able to pick up a Pioneer SX-780 for $50 today. It does have some issues. It powers on and all the lights come on. The relay doesn’t click on nor does the FM meter move. All the fuses seem to be intact. Any ideas on what and where to start troubleshooting? Thanks so much!

Hi, I came across a faulty SX-780. When opening it and looking for the problem, I went straight to check the fuses. - Hey... !!! . Where are the fuses ? Surprise ! - No fuses ?! To my surprise ... there is no fuse board in that unit ! (Fuse Assembly Circuit Board AWR-169 or AWR-171)...

Newb here. I’ve had an SX-780 since 1985 that I purchased from the original owner. I had it serviced twice to replace STKs. I believe the right channel was replaced both times because the left channel STK looks original. Regardless, any replacements were done in 1990 or before. It has not been...

THE INCIDENT I was listening to XM Radio over the AUX input when I heard the audio fluctuate. I thought maybe there had been a power spike (despite being plugged into a surge protector). Suddenly the right channel became very weak and garbled. Occasionally it would break back through to full...

Hello all, I have a SX-780 with voltages on the STK-0050 pins that are slightly high. (This based on other posts here) Electrolytics on the amp/power board have been changed Transistors on the amp section all changed per recommendations on other posts here. Transistors in power supply circuit...

I have a pair of Aiwa SX-780's and a pair of MCS 683-8224-20 (2-way) speakers. They have been sitting in the garage for about 2 years or so. I picked them up on CL a while back for cheap. The foam and speakers are good, but I believe the crossovers need some work. I hooked them up when I first...

I have assembled a BOM for the AF board (GWK-118 only) in the SX-780 for vetting if anyone is willing to look it over. It is not intended to include the STK0050s, the protection relay, front panel controls or the Tuner board parts. I have collected these from multiple posts and old lists on...