SX-980 power supply/protection circuit board problems

[GTS Dean]

I'll start here by stating that despite reading numerous expert warnings - with Service manual in hand, I took a working receiver, gingerly measured some terminals and using what I thought to be very careful technique, I ended up shorting some board terminals and how I have no audio output from either the preamp or the amplifier circuits.

There. I've admitted to being an idiot. I feel like David Niven in Bridge Over the River Kwai - "Oh my God, what have I done?" I still have Tuner and Input functionality.

Below are the voltages I have on the 2 boards:

The Power Supply. The first column is terminal #, second is post-failure value, third is reading pre-failure. (I think I arc'd #19 and #20) and then popped Fuse 6. When 6 popped, the circuit protection relay was cycling about every second or two. When I replaced the fuse, the relay clicks as normal 7 secs after switch-on.

123.4V AC input
1. 92.6
2. 92.5
3. 26.88
4.
5. 39.3 39.3
6. 39.8 39.3
7. 39.8
8. -54.3 16.7
9. 47.8
10. 53.8 53.4
11. 53.8 53.4
12. 20.7 20.54
13. 20.67 20.54
14. 20.67 20.46
15. 0 6.4mv
16. 24.72 59.1
17. 24.75 59.0
18. 24.76 1.73
19. 4.11 xx short
20. 71.5 xx
21. 4.48 xx
22. 0
23.-0.46
24.-0.46
25.-25.35
26.-25.35
27.-13.84
28.-53.7

Circuit Protection - these are post failure.

1. 20.3
2. 53.7
3. 0
4. 24.45
5. 0
6. 0
7. 0
8. 0
9. 24.82
10.71.7

 

[Watthour]

Just for complete clarity, from which board (numbers) are each of the sets of readings? Also, what voltages are AC and DC? This should be fairly easy with a bit more information.

 

[zebulon1]

The voltage at pin 20 is way high for the DC supply. If I'm interpolating your post correctly.
Don't run it any more.
Build a DBT.
Rebuild the power supply. Probably needed it anyway.

Why were you taking readings?

Old list needs checking.
q1 2sd712 100v 4a 30w 55-300hfe 8mhz
512-KSC2073TU npn to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.54
q4 2sb682 100v 4a 30w 55-300hfe 8mhz
512-KSA940TU pnp to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.54
neither side is going to come close to an amp of current, no less 4 amps


q2 2sc1735 100v 0.5a 0.8w 55-300hfe 130mhz
512-KSC2383YTA to-92L ecb 160v 1a .9w 50mhz 160-320hfe $0.17
q3 2sa850 100v 0.5a 0.8w 55-300hfe 130mhz
512-KSA1013YBU to-92L ecb 160v 1a .9w 50mhz 160-320hfe $0.17 (R=60-120, O=100/200, Y=160/320)


Q5 2sd712 512-KSC2073TU
q6 2sc945a eCb 50v .15a .25w 300mhz 40-700hfe
512-KSC2383YTA to-92L ecb 160v 1a .9w 50mhz 160-320hfe $0.17

d8 mz-140 512-1N5244B Fairchild 14 V, 0.5W Zener
d9 mz-130 512-1N5243B Fairchild 13 V, 0.5W Zener


awr-164
c19,c20 4.7uf 50v 647-UPW2A4R7MDD 4.7uf 100v $0.14
c17,c18 47uf 16v 647-UPW1V470MED 47uf 35v $0.16
c24,c25 47uf 25v 647-UPW1V470MED 47uf 35v $0.16
c11,c12,c15,c16 220uf 80v 647-UPM2A221MHD 220uf 100v $1.02 ea
c13 220uf 35v 647-UPW1V221MPD 220uf 35v $0.28
c23 2200uf 35v 647-UPW1H222MHD 2200uf 50v $1.49 ea

 

[GTS Dean]

Thanks for the replies, gentlemen. I'm not close to my hand-written notes for AC/DC comments, but suffice to say that the vast majority are DC. The reason I was pecking around was the semi-frequent protection circuit trips when I first got the receiver last month. I went to the amp boards and adjusted idle current and center L/R right to spec with some improvement noted. I just started at the front end and was noting current readings to compare with the manual as I progressed toward the amp boards.

Zeb - I'm sure those catalog numbers mean the world to you, but I'm only able to decipher about 40% of your list. I'm very competent mechanically, but I have practically zero skill level with pc board component replacement. I'm going to have to take it to San Antonio or Austin to have this put right by a competent professional. Meanwhile, I'll work in my comfort zone recapping my 37 year old Bose 601-1 crossovers and getting them ready for the 980's return. Would anyone care to ballpark what a shop repair ticket is likely to run on this? Is $150-250 in the ballpark?

 

[zebulon1]

Bring a copy of the post with you to the shop. This list will save some time and hopefully some money.
Have the tech rebuild the power supply.
Two hours or so and $20 in components retail.
Do not have him install NTE components. If he says he uses Fairchild and On semi, he's probably got it going on.
The list has what's needed.

 

[GTS Dean]

This is the most awesome Forum on the entire internet!

 

[mattsd]

Here is a list with a Mouser BOM for quick ordering:

Power Supply Assembly (AWR-156)

AWR-156: C11: 220uF 80v CEA: 647-UPW2A221MHD6 220uF 100v
AWR-156: C12: 220uF 80v CEA: 647-UPW2A221MHD6 220uF 100v
AWR-156: C13: 220uF 35v CEA: 647-UPW1H221MPD 220uF 50v
AWR-156: C15: 220uF 80v CEA: 647-UPW2A221MHD6 220uF 100v
AWR-156: C16: 220uF 80v CEA: 647-UPW2A221MHD6 220uF 100v
AWR-156: C17: 47uF 16v CEA: 647-UPW1E470MDD 47uF 25v
AWR-156: C18: 47uF 16v CEA: 647-UPW1E470MDD 47uF 25v
AWR-156: C19: 4.7uF 50v CEA: 647-UPW1H4R7MDD 4.7uF 50v
AWR-156: C20: 4.7uF 50v CEA: 647-UPW1H4R7MDD 4.7uF 50v
AWR-156: C23: 2200uF 35v Snap-In (10mm LS): 661-EKMH500VNN222MP3 2200uF 50v
AWR-156: C24: 47uF 25v CEA: 647-UPW1E470MDD 47uF 25v
AWR-156: C25: 47uF 25v CEA: 647-UPW1E470MDD 47uF 25v

AWR-156: Q1: 2SD712: 863-MJE15032G
AWR-156: Q2: 2SC1735: 512-KSC2383YTA
AWR-156: Q3: 2SA850: 512-KSA1013YBU
AWR-156: Q4: 2SB682: 863-MJE15033G
AWR-156: Q5: 2SD712: 863-MJE15032G
AWR-156: Q6: 2SC945: 512-KSC2383YTA

AWR-156: D8: MZ-140: 512-1N5244B
AWR-156: D9: MZ-130: 512-1N5243B
AWR-156: D10: LZ230: 512-1N4748A
AWR-156: D11: LZ230: 512-1N4748A

BOM List:

647-UPW2A221MHD6 | 4
647-UPW1H221MPD | 1
647-UPW1E470MDD | 4
647-UPW1H4R7MDD | 2
661-EKMH500VNN222MP3 | 1
863-MJE15032G | 2
863-MJE15033G | 1
512-KSC2383YTA | 2
512-KSA1013YBU | 1
512-1N5244B | 1
512-1N5243B | 1
512-1N4748A | 2

 

[GTS Dean]

And, a happy ending! Parts were dirt cheap - and service was ... Worth It!

 

[kevzep]

And, a happy ending! Parts were dirt cheap - and service was ... Worth It!


View attachment 1227925

Rebuild the power supply board, the tech's assessment of that is not correct.
Not saying he did bad work, but, if you wan this unit to be reliable for the foreseeable future, this work needs to be done.

 

[GTS Dean]

He said that the whole chassis appeared to have been freshened up with new components fairly recently. From that, he made the recommendation not to go further. He works for the top AV store in San Antonio and if the PS gives trouble later, I know the owners personally. I'm not here to mediate a professional squabble, but I do value and appreciate your opinions.