I grabbed one of these from someone on Facebook because it would be perfect for hooking a turntable up to some speakers. I got it home and noticed the right channel didn't work with headphones or speakers and you would get occasional static sound in the right when turning the volume knob. I took the cover off and could tell someone's been in here, likely replaced the driver transistors as the heatsink is inverted from its original position and the solder doesn't look OE, I see flux in some of those joints. Before I give this back to the guy, do you think it's worth trying to track down the cause? I am cool if I have to invest some time and money within reason but the fact that there was prior work gives me pause. What do you think?
I read this post first...
I read this post first...
I was able to get the manual linked in that other thread. I can read the schematic well enough but I am not skilled in testing the components. I have a voltmeter but not sure where to even start. Again, I think either someone attempted to fix it previously or did fix another issue but now this issue is happening. The owner claims he never had it repaired.
Ok, now I've had time to dive into this thing a bit more and I really think someone was in here even though the previous (original) owner says he never had it serviced. The circled heatsink compound almost looks like someone had it out and accidentally laid it back in upside down and the transistors put some of their compound in that area. Also it looks like c353 was replaced as it's different from all of the other 10u50v caps around it. I'd really like to diagnose this if anyone is willing to help guide me a bit. The symptom is the right channel only plays heavily distorted audio whether on speaker a, b or headphones.
small update, I looked over the back of the mainboard and saw what I thought were sub-optimal solder joints and re-did them (about 10) and suddenly everything started working. I put it all back together and put it in my system and then noticed that every once in a while the right channel would "pop" and fade out to silence then after a few seconds would come back.
If it suddenly started working it does sound like poor joints could be an issue.
Check around all parts that run hot and all parts fixed to heatsink. Look for cracking around joints.
Poor joints often look like this:
Although your issue doesn't sound quite like this... check the speaker relay (you can often tap them) to make sure there is no poor contact internal. That is a very common issue across all makes and models.
Check around all parts that run hot and all parts fixed to heatsink. Look for cracking around joints.
Poor joints often look like this:
Although your issue doesn't sound quite like this... check the speaker relay (you can often tap them) to make sure there is no poor contact internal. That is a very common issue across all makes and models.
Thanks, I've gone and closely inspected all of the joints and re-heated each one that looked suspect and now I just get a random set of pops every so often so that's better? But now harder to reproduce. What do you mean by speaker relays? I only see one relay and it's the one that trips when the output voltage goes to high and puts the unit into speaker protect mode.
A speaker relay is just a set of contacts in series with the speaker that provides a delay on switch on and trips out under fault conditions.
Your description of how yours operates sounds like a 'speaker relay' but also be aware some units use a relay to turn the power off when the unit is put into standby from a remote control for example (if this one has such a feature).
Your description of how yours operates sounds like a 'speaker relay' but also be aware some units use a relay to turn the power off when the unit is put into standby from a remote control for example (if this one has such a feature).
I see three total relays, one for enabling the tape output monitor, the safety shutdown relay and the main power relay. Would a good diagnostic step be to monitor voltage with a voltmeter on the right channel and wait for the popping and see if there's a fluctuation and then just work backwards through the circuit until I no longer see the fluctuation?
You can try but you may not see much with a meter although an oscilloscope would certainly show it.
Wait maybe I was misunderstanding how the speaker relay functions. Is that the relay your hear click a few seconds after power on and it's energized in order to let the signal flow to the speakers and on overload, it's de-energized? I really wasn't looking at it in the schematic realizing the signal had to flow through it to get to the speakers and instead when it's closed, the signal got re-routed or dumped to a cap or something.
That's the one. You will get no audio at all from the speakers until that relay clicks on. When its open the amp just runs 'no load' which is fine for solid state amps.
thanks, I guess I had it confused with something else I had read about some amp that a similar relay would dump to a cap for some reason. I'm not too suspicious of this relay causing the pops but I suppose anything is possible. Right now it's been playing for over 5 hours without a pop but I don't feel like I've fixed anything 🤣🤣🤣
if I wanted to replace it, how does one choose an appropriate replacement when the sony part number doesn't seem to have a cross reference when googling? It's a dh2su 12vdc 2a 120vac relay.
Its likely a common size. You have to look at dimensions and pin out configuration. Also coil resistance as well as voltage is important. Higher R is OK but don't go to low. Then search suppliers products. The 120 vac will be the contact rating.
It comes up in a search:
It comes up in a search:
Oh ok so it's not too specific, anything that meets the criteria and fits the spot is ok? thanks. It started acting up again after playing for several hours. I had the cap off of the relay and poking it didn't seem to affect anything so I am suspecting either still a bad solder joint or transistor or maybe something else getting too hot for it's liking. I've ordered an oscilloscope as I plan to keep doing this and I can't thank you enough for continuing to respond to this thread.
If poking the relay has no effect its probably not going to be that. As you can access it you can clean the contacts anyway, just soak some paper in iso or similar and pull it through the contacts.
Yeah I had already cleaned it up. I'm thinking transistor at this point but will need the oscope to trace the signal more easily. I got a dual channel one so I am hoping I can put one on the output of say the volume control circuit and one at the speaker output and that will help me isolate it more quickly by working them closer to eachother. In the mean time I am taking the wiring diagram and clearly highlighting the right channel signal path to make it easier to find places to probe.