revisiting my sx-850 no sound issue..

Thanks Pete....here they are

Q5 E=7.7 and jumping around between 5 and 9 volts
C= .68
B= 4.98 and jumping all around between 4 and 9 volts

Q6 E= 0
C= 0
B= .68

Q7 E =0
C= 35.7
B= 0
 
check idle biases both channels ..if ok pull one end of d5 on protect board and see if relay clicks. if bias is wrong one or both channels it needs attending to first .
 
sounds good. I was just watching a video on adjusting the bias, I,ll have to pick up a set of long probes for my meter and a couple resistors! I miss the old days when there were Radio Shacks and electronics supply stores all over the place. :)
 
no need to load the outputs .or inputs for that matter .vol down no inputs select aux is standard instructions . check every 5 minutes for 20 mins .
 
Ok... finally got around to the sx 850... Heres how I checked bias ...power on..no load...pulled jumpers and took readings. I took readings before I pulled the jumpers and the readings seemed to jump around,so I pulled the jumpers. As per the procedure,VR1 and VR2 were checked and set to 0v....VR3 and VR4 were set to 20 mv. After setting,I let the receiver warm up for 20 minutes and rechecked. A couple needed slight adjustment but it looks like the bias is set pretty well. I hope I did it right! So, still no relay click. As a note,the receiver has sat for a few days and when I plugged it in and turned it on today,the relay did click on,then off after 10-15 seconds, which is an improvement. Next step? I have a feeling that I,ll be rebuilding both boards,but would like to take it a step at a time just to see what the main problem was. Any thoughts are appreciated! Chuck

ps... it seems that the Q7 on the protection board has been an issue.. I may replace that tomorrow just to have that taken care of.
 
And I changed Q7 on the protection board and still no click......Disconnected one of the legs from D5 on the protection board and I have a click! Is this telling me D5 is the issue,or is it something connected to D5?
 
you cut off the over current sensing circuit . q1 q2 etc .
what are the voltages at
5
6
7
8
protect board ?
are bias and dc offsets ok ?
 
Thanks pete.....voltages at 5,6,7 and 8 are all zero. I set the bias last nite, I think I did it right,look at post # 30 above. VR1 and 2 were set to 0 and VR3 and 4 were set at 20mv. Not sure on how to check DC offset on the 850. Chuck
 
Thanks Pete.... any idea what the replacements for those transistors are? I,ll check dc off set and post. Thanks again.
 
2sc869 are originals looking at schematic .
you should also test the diodes .
the subs for the transistors should be on a list on AK
 
Thanks again Pete....I checked offset and both right channels ( A and B) held at 0. Both left channels were bouncing around a little, from -15 to + 15 mv... Not sure whats acceptable.
 
Thanks to "Suitekids" for the KSC1845 FTAs! Mouser was out and he passed along a few to help me out. I have a few more caps to replace on the protection board,but today finally got around to replacing Q1 and Q2, the diodes and some of the caps. Powered up the unit and I finally have a relay clicking and good sound. I hooked up a set of Infinitys and my old Tascam cassette deck to test it out....so far so good.I,ll finish up the remaining caps tomorrow and then I,ll have to do some serious cleaning on these switches and pots. I,m getting some pretty good crackling from the Bass switch whenever its turned. It appears to have been banged hard at one time and the stem had to be tweeked when I got it to straighten it out. I,m hoping it doesnt need to be replaced, but we,ll find out! Thanks to everyone for the help in getting the 850 back into service, its been a great platform to learn on! Chuck
 
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