Houston, I've got a problem....

[twofish]

Hi folks,

Well, it seems that I have just gotten my introduction posting done and I already need some advice/help.

I recently purchased an SX-850 receiver. Everything was working great until last night. After listening to my turntable for a short time on "Phono 1" the right channel started to malfunction. The output for that channel seemed to fade quickly to a stop and then a crackling almost violent popping began to occur.

I switched the turntable to "Phono 2" input to see if that made any difference.....same thing was happening.

I then disconnected the turntable altogether thinking it was the turntable itself and the problem was still occuring. The tape outputs, aux. output, FM and AM are all clean and fine with no malfunction at all.

I shut the unit down and let it cool off completely. After repowering it was okay at first but then the problem started again after only a minute or so.

Again, I am new here so I am not sure that I have used the search function to its fullest but so far from what I have read it seems to possibly point to the phono preamp transistors for the right channel or perhaps the phono preamp itself. I really have no idea since I have no technical electronics experience or capabilities.

I would be grateful for any advice/help/guidance that anyone has.

Thanks,

PS: Please forgive the long post and description of the problem if it is lacking.

 

[avguytx]

Have you cleaned and lubed the switches and pots with Deoxit per chance? First thing I'd try myself. Nothing like a good description of the problem. So many write so little....

 

[markthefixer]

sx850 sx-50 recap and retransistor parts list awf011

This is a very well known problem, there are transistor problems, so they need to be replaced.... while you're in there, re-capping will just add a few bucks onto the parts costs, and the results will please your ears...

The parts are on the phono amp board, labeled awf011. Download the sx850 AND the sx950 manuals, the 850 and 950 are close enough alike that the 950 manual will help make up for the poor 850 manual.

For parts in The USA:
www.mouser.com , mouser.com parts numbers:
during checkout, first class mail shipping becomes available for about 4 bucks
this place has no minimum order, or surcharge.

2x 512-KSA992FBU @ $0.06 ea PNP low noise high gain af amp ecb lead-layout fairchild for Q1 & Q2
4x 512-KSC1845EBU @ $0.06 ea NPN low noise high gain af amp ecb lead-layout fairchild for Q3, Q4, Q5 & Q6

2x 647-UPW1H010MDD @ $0.23 ea for C1, C2 1uF 50V input coupling, signal path
2x 647-UPW1H3R3MDD @ $0.23 ea for C11, C12 3.3uF 50V output coupling, signal path
1x 647-UPW1V101MPD @ $0.15 ea for C17 100uF 25V(35v) + power filter
1x 647-UPW1V221MPD @ $0.56 ea for C18 220uF 16V(35v) - power filter
2x 647-UPW0J331MED @ $0.39 ea for C7, C8 330uF 6V internal filter

All have been checked and are currently in stock.

BE CAREFUL INSTALLING THESE TRANSISTORS, the lead layout is different!!
the original parts are BCE and the fairchilds are ECB...
thus in both the center lead IS the collector (c) but the two on the outside are REVERSED!!!!!
That means the flat on the transistor will face in the other direction.

The capacitors have the minus terminal marked with a minus, the longer lead is plus.

Change each part one at a time. Lead arrangements on EVERY part mentioned are critical and non-negotiable.

Good luck, watch out for the heat sensitive capacitors, the ones with the clear plastic ends...

Of course, holler if you need more detailed help. Although even if new to this, open the bonnet (their words, not mine) and bottom and study it with the manual (at least LOOK at every manual page, later on you can say "oh yeah, I saw something like that") so it isn't alien territory.

Do you have desoldering / soldering equipment ?

 

[m4rz]

Markthefixer I wish you were local! Always a fountain of knowledge and assistance.

 

[twofish]

Thanks guys for the responses.

Markthefixer, unfortunately or perhaps fortunately for the unit, I do not have any soldering or desoldering equipment or really any electronic repair/testing tools.

I plan to print the manuals and take off the bonnet and bottom tonight to atleast take a look at what I am dealing with as you have suggested. Although at this point I am not feeling particularly confident about trying to make the repair. I guess I am a little concerned about creating more problems than I might eliminate.

Thanks again for such a timely and thorough response and I may well need some more detailed advice and/or professional help.

twofish