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Left channel has gone silent. Have tried everything I can think of to resurrect it, short of sending it off to a tech. De-Oxit on all controls improved nothing. Was working fine for years then just one day, no sound. Can anybody give me some insight in where to start looking for a fix?
Thanks
-k-
Follow Ups:
I'll follow up on Airtime's suggestion. That receiver is chock full of wire wrap connections. Try soldering all the wire wraps to the post. use a hot iron and solder just the top turn to the post. That has cured several Pioneer's for me. The wraps don't get loose, they do corrode, however. Do a search, I've posted several times on this with the correct procedure.
Jerry
Audio
there are some good suggestions in these posts and the first thing is you want to see if you have voltage on the output transistors.The 737 uses complementry pairs of outputs as I remember so your going to have a plus and minus B+ rail and thats obviously working because you have one channel.
Let us know how well versed you are at using a voltmeter and we can walk you thru some troubleshooting.Usually outputs short out and they take out a B+ fuse or a fuse type resistor for the defective channel.
I just looked at the service manual, you can try reversing the pre out main in jacks, just put left to right and right to left channel, then you can tell if the problem is in the preamp section or the output amp seftions.
A common problem I've encountered with every Pioneer of this vintage that has passed through my hands, including two SX-727s, is that the contacts on the protection relay corrode and the signal is lost in at least one channel or at least crackles horribly. I can't explain why, but it's always been the left channel.
With the unit unplugged, pull off the top cover and the perforated metal cage around the finals. The relay will be just about in the center of the chassis. Carefully pull the cover off, watching for the two tabs on each of the long slides. Take a small strip of crocus cloth (abrasive fabric like a high hundreds sand paper), slide it between the contacts and go back and forth until they look shiny again. Try the receiver out to see if that fixed the problem.
Now, lots of other things could be wrong including blown components, broken switches and such, but this is the most common problem I've found after dirty switches.
Good luck,
- JP
I recently aquired an SX-727 also and the left channel is quiter than the right and sometimes cuts out. I would like to clean this relay. What does it look like? I take off the top, remove the black perforated cage and then what am I to look for?
Thanks,
ed
Ed, if you've already cleaned the switches, and the sound sometimes returns or the crackle diminishes when the volume is turned up, then I'd say a dirty relay is a strong possibility. When you remove the four screws holding the black perforated sheet metal cage from the top of the output transistors, near dead center in the chassis will be the relay. It should be a box-shaped component roughly an inch square and an inch and a half tall. The cover will be transparent and facing front to back, it'll look like it contains a small black drum with four thin metal strips on the right and the contacts at the bottom. It's the only largish component on the top of the chassis in the middle just to the front right of the most forward large black filter cap. The set of contacts that are important to clean are those on the inside, not the outside.
Good luck,
- JP
Correct, I have cleaned the switches. Thanks for the description. I will try cleaning the relay hopefully sometime this week.
Ed
Didn't those units use those wire wrapped posts that crapped out a lot?
Try seeing if one of the wire wraps inside are loose by pushing gently with a pencil.
charles
Hello,My old SX-550 has fuses in the power amp output, one per channel. I don't know if yours is the same, but it might be worth looking into.
Mario
First try a different input. Other than that it would be best if you had an oscilloscope to see where the signal ends? But if you can use a volt meter you may be able to at least see if "voltage" is getting to the amp stage.
I would have to assume there is no seperate preamp/amp jacks on the rear?
I've found that many times it is a bad contact somewhere in the control section. It is unusual for a channel to just go silent without a little pre-death noise.
charles
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