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Hello-
I've posted this problem before . . . thought I had it fixed, but evidently not. The receiver works perfectly, but intermittently shuts down output to the speakers (ie. a rather loud pop is sent through the speakers concurrently with the protection circuit kicking out, you can then hear the circuit kick back in and the stereo starts playing again in one or two seconds). There is no power loss while this is happening--all the lights stay on. I thought I had the problem solved. There was a very bad/cracked solder on the protection circuit board that I fixed. This fixed the problem for about a month . . . then it started again--the exact same symptoms. I've replaced every transistor and capacitor on the protection circuit board with the exception of two transistors and two capacitors that my electronics store couldn't identify/didn't have in stock.
Questions:
Can the problem be isolated to the protection circuit board from the above information?
What am I missing?PS: I've cleaned all the switches/pots
Thanks a bunch. I have a love/hate relationship with this thing right now!!!!!!!!!!
Follow Ups:
Well, I got home last night and tested my receiver for DC offset . . . no apparent problem there (left and right channels measured @ -5 to -6 mV). I then removed the relay switch between the protection circuit and the speaker switch assembly . . . sanded the contacts . . . then replaced. So far, the receiver has not failed . . . but I won't hold my breath . . . I'll let her run some more tonight . . . the problem has been intermittent, so a long testing period will increase my comfort. Thanks for all the advice from yessir and CULater.
and you must've seen my post on follow-ups...My comments weren't directed at anyone in particular, actually more toward posts I encounter while lurching. I'm pretty much a newb ( hence "yessir" ) and I like to read advice/ideas and I'm interested to know what works and what doesn't, aside from what I can garner through hands-on work.
I'm glad to here the sanding worked (for now..), I hope that was the fix and you get to enjoy problem free listening for a long time!
Incidentally, I'm going to be trying a lot of tweaks on sx750, which I believe is fairly similar to the sx850, and I'd be happy to post my results if you're interested.
Of course I'm interested!!
just need to recover finacially from the holidays...
I have the circuit diagrams for the sx850, for when I go to fix mine! If you want them I can scan them in for you.
I'd love them. Just send them to my email in my profile
Have you checked the DC Voltage levels at the output? If not, then I'd suggest that you read EchoWars' excellent thread at AudioKarma...could be nothing more than output bias needs a little trim adjustment.
Cheers,PBG
Okay, say I test for DC output and it is way too high. What then? I'm not exactly up on all the techno-jargon . . . I'm a novice, but would like to learn and am not afraid of jumping in. Thanks for your help.
Well, yessir is right - you can adjust the trim pots to get the DC levels down to a few mV, but only if you feel like you have a basic confidence in doing a little electrical work. It really isn't hard at all, especially if you have a service manual for the receiver. If this is a keeper, a receiver that you really enjoy, I'd highly recommend getting a copy of a service manual for it - they are available via ebay, www.stereomanuals.com, etc., for about $20 or less. You might even be able to get a copy of the page from the manual showing where the trim pots are from one of the folks here or at AudioKarma. (sorry, but I don't have that service manual myself)Read all the way through the thread on DC offset at AudioKarma - its a great primer on how to get that DC offset under control, and improve the sound to boot. Even if this isn't the source of your current problem, I'd suggest doing it after you get the SX-850 back working again. But that's just me - I am an engineer, and have to tinker with stuff all the time anyways.
Cheers,
Adjust the trim pots. Make SLIGHT turns and see how this adjusts DC. This is really about adjusting DCoffset on the output transistors and you should take a reading off of the 'sistors themselves.My advice; don't mess with that stuff unless you're really confident of what you're doing. Good way to get zapped or fry components. I'll bet it's the relay anyway.
The switch relay is dirty, you need to sand the contacts. Very carefully pop the cover off, and using a very fine sandpaper strip or a fine, thin and small file depress the contacts and GENTLY sand them, then release and sand other side across the contact bridge.
Try and use a lint free cloth or can of air to remove any residue left from sanding.If the relay is anything like the one in the sx750 it's a bit of a bitch to get the cover off. If you're not confident, remove the relay from the board before you proceed; it'll be easier that way anyhow.
If this doesn't work there could be myriad other problems, but the symptoms sound like dirty relay contacts.
I'm revealing my ignorance here. What relay switch are you speaking of? What does it look like? Where exactly do I need to look for it. I've got a schematic . . . does that help? I really appreciatte your help.
A little black-box, about 1" by 1" by 2" cube. It'll probably say "DEC type MS4U/ 24VDC " or something similar, if the model is similar to the SX750.I'd also check to make sure all of the resistors in the area are not out-of-value. Get yourself a resistor color code cheat-sheet.
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