SX 950 - Low voltage

grandpaslab

Active Member
I've got a 950 that came in with a blown output, blown main fuse. I've done the following:
  • replaced all outputs with onsemi subs
  • replaced all transistors, diodes and electrolytic caps on the main amp board
  • replaced all transistors, electrolytics on the power supply board
  • replaced filter caps
  • replaced main rectifier diodes with 621-10A04-T
I have NOT replaced the STV-4H.

Unit now powers up but is in protection. Voltages are low across the board, e.g. 28v at the outputs where it should be ~49v.

Can anyone suggest next test(s) to localize the voltage issue?


Transistor subs were as follows:

Main amp
2SC1628 -> KSC3503 (Q7, Q8)
2SA818 -> KSA1381 (Q5, Q6)
2SD381 -> KSC2073 (Q3, Q10)
2SB536 -> KSA940 (Q11, Q12)

Power supply
2SB507 -> KSA940 (Q2)
2SA720 -> KSA1013 (Q4, Q6)
2C1318 -> KSC2383 (Q3, Q5, Q7)
2SD313 -> KSC2073 (Q1, Q8, Q9)
2SC869 -> KAC2073 (Q10)
 
This is what I use in the power supply with great results:
Q1-KSC2073
Q2-KSA940
Q3-KSC2383
Q4-KSA1013
Q5-KSC2690
Q6-KSA1013
Q7-KSC2383
Q8-KSC2073
Q9-KSC2073
Q10-KSC2383
Also replace D1 with 1N5244B,and D2 with 1N5243B

Also check your transistor leg placements. On both boards.
 
Thanks for that. Double-checking my transistor pinouts will be my next step I guess. Forgot to mention, I already replaced D1 and D2 on the power supply board.
 
This is what I use in the power supply with great results:
Q1-KSC2073
Q2-KSA940
Q3-KSC2383
Q4-KSA1013
Q5-KSC2690
Q6-KSA1013
Q7-KSC2383
Q8-KSC2073
Q9-KSC2073
Q10-KSC2383
Also replace D1 with 1N5244B,and D2 with 1N5243B

Also check your transistor leg placements. On both boards.

Hmm, looking over your list it looks like my subs are the same except for Q5 and Q10, which are reversed. I'll have to double check those parts.
 
Unit now powers up but is in protection. Voltages are low across the board, e.g. 28v at the outputs where it should be ~49v.
The voltage at the collectors of the outputs? There's nothing in the PS that will affect that, save for a bad transformer, amazingly low line voltage, or horribly bad filter caps.

Or, say, you have it connected to a DBT. ;)
 
The voltage at the collectors of the outputs? There's nothing in the PS that will affect that, save for a bad transformer, amazingly low line voltage, or horribly bad filter caps.

Or, say, you have it connected to a DBT. ;)

D'oh! You mean it could be that low just because it's on a DBT?

I'm separated from the 950 until Monday, but I'll try it without the DBT and report back.
 
Geez, absolutely, when on DBT you are not on house power to protect the precious output transistors. Depending on the wattage of bulb you used the voltage will vary, a 60 watt bulb will have lower voltages than a 100 watt bulb. How did DBT work out? Got relay click? Bulb dims? Tickle the dragons tail? If so turn down V3 & V4 fully counterclockwise with the unit powered off. Then you can apply full house power of course if you passed the tests I just mentioned. Then you can "tickle the dragons tail" on full house power to see if idle current is adjustable. If so you should have a successful restore.
 
tickling the dragon's tail(R) is a trial idle current set on DBT

without DBT, it's just plain "idle current set".... :D

You are seeing DBT voltage drop at the unit, the AC voltage is so low even the protect circuit thinks it's turned off.
I use 100 to 150 watts.

IF the DBT is NEEDED, higher wattage of the lamp doesn't matter, the power absorbed by the unit will be minimal.

Lower wattage DBT just causes sweats, intestinal distress, panic attacks, nightmares and unpleasant (unneeded) surprises.
(ALL kinds of weird shit...)
 
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Yep, with the DBT out of the loop voltages are normal.

Now I'm trying to zero the outputs following the procedure in the SM, but VR1 and VR2 are having no effect. Left channel holds steady at about 5V, right channel is at -0.6.
 
You gots three regulated voltages coming into the amp board....+/-51V and +36V. These three (along with ALL the other regulated voltages on the power supply) need verification.
 
Current voltages below. A couple seem clearly wrong:
PS pin 4 at 0
PS pins 8-10 (and main amp pins 4/5/19/20) should be ~36v?

Power supply
pin volts
1 0
2 0
3 0
4 0
5 0
6 5.8
7 5.8
8 3.6
9 3.6
10 3.6
11 2.23
12 0
13 -13.2
14 -50.4
15 -18.1

Main amp
pin volts
1 -50.3
2 -50.3
3 0
4 3.67
5 3.67
6
7 5.8
8 5.8
9 0
10 4.8
11 4.8
12 4.8
13 4.8
14 49.9
15 -49.9
16 -50.5
17 -50.5
18 0
19 3.67
20 3.67
21 0
22 5.8
23 5.8
24 0
25 -0.6
26 -0.6
27 -0.6
28 -0.6
29 50
30 -50
 
R9 and R10 on the PS board have failed open. Don't have those values with me, will report back once I've replaced them.
 
Did you change out Q5 on the power supply to KSC2690? Your both board readings are not healthy. Did this unit start up OK off the DBT with relay click?
 
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I did sub a KSC2690 at Q5. I pulled it today to do a basic diode test, it seems fine. Pinout was correct. Lifted one leg of a bunch of resistors in the neighborhood, so far all have tested within spec. Next I think I will check Q1. Q3 and Q7.
 
You zd1 is shorted, shutting down 2,3,4,5 completely, while starving 6,7,8,9,10,11

quite frankly, every transistor bears replacing, although q2, q4 & q6 are behaving right now.

while q1 may have not been overloaded, maybe Q8 blew zd1.

from my notes:
AWR-101: C10: 470uF 80v ACH-038: 647-Upw2A471MHD 470uF 100v
AWR-101: C11: 470uF 80v ACH-038: 647-Upw2A471MHD 470uF 100v

or

AWR-101: C10: 470uF 80v ACH-038: 680µf 80V 667-ECO-S1KP681BA
AWR-101: C11: 470uF 80v ACH-038: 680µf 80V 667-ECO-S1KP681BA

--------------- from my notes:----------------
EchoWars: My own choice to replace the big three-legged caps.
EchoWars: AWR-101: C10: 470uF 80v ACH-038: 680µf 80V P7494-ND (Digikey) goat67: (mouser) 667-ECO-S1KP681BA
EchoWars: AWR-101: C11: 470uF 80v ACH-038: 680µf 80V P7494-ND (Digikey) goat67: (mouser) 667-ECO-S1KP681BA
EchoWars: Mark, use these once to replace the originals,
EchoWars: and the way they fit so solidly will convince
EchoWars: you that when you have a cap with 10mm LS that
EchoWars: needs replacing, look for a proper snap-in.
EchoWars: Those tall radials with the stretched leads
EchoWars: aren't near as stable, and with their size
EchoWars: they need to be.

EchoWars: Also, IIRC, those 1000µf 25V & 35V caps may
EchoWars: have been something else entirely on the board.
EchoWars: I think the last 950 here had a 2200µf 35V cap in that spot.
EchoWars: I also seem to recall that it also was a 10mm LS cap,
EchoWars: and I stuck another snap-in in that spot.

----------------------------------------------------------------------------


AWR-101: C12: 1000uF 35v ACH-039: 1000uf 35v 647-UPW1V102MHD
or
AWR-101: C12: 2200uF 35v ACH-039: 2200uf 35v 667-ECO-S1HA222BA

EchoWars: C12 667-ECO-S1HA222BA 2200uf 50v 10mm lead spacing snapin enlarge to 1/16 hole

EchoWars: C13 667-ECO-S1HA102BA 1000uf 50v 10mm lead spacing snapin enlarge to 1/16 hole

AWR-101: C13: 1000uF 25v CEA: 647-UPW1E102MPD6 1000uF 25v

AWR-101: C14: 220uF 10v CEA: 647-UPW1V221MPD6 220uF 35v
AWR-101: C15: 470uF 63v CEA: 647-UPW1J471MHD6 470uF 63v
AWR-101: C16: 47uF 16v CEA: 647-UPW1V470MED 47uF 35v
AWR-101: C18: 47uF 50v CEA: 647-UPW1H470MED 47uF 50v
AWR-101: C19: 47uF 35v CEA: 647-UPW1V470MED 47uF 35v
AWR-101: C20: 100uF 63v CEA: 647-UPW1J101MPD6 100uF 63v
AWR-101: C21: 47uF 16v CEA: 647-UPW1V470MED 47uF 35v
AWR-101: C23: 100uF 35v CEA: 647-UPW1V101MPD 100uF 35v


AWR-101: Q1, Q8, Q9 2SD313 +51, +13.9 +5.4 series pass
512-KSC2073TU npn to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.66

AWR-101: Q3 2SC1318 pos suppl feedback and drive
512-KSC2383YBU to-92 ecb 160v 1a .9w 50mhz 160-320hfe $0.17

AWR-101: Q5 2SC1318 +36v series pass reg
512-KSC2690AYS to-126 ecb 120/a160 1.2a 20w 155mhz 35-320hfe $0.40

AWR-101: Q7 2SC1318 +28v series pass reg
512-KSC2690AYS to-126 ecb 120/a160 1.2a 20w 155mhz 35-320hfe $0.40


AWR-101: Q2 2SB507 -51v series pass
512-KSA940 pnp to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.62

AWR-101: Q4, 2SA720 -51v feedback & drive
512-KSA1013YBU to-92L ecb 160v 1a .9w 50mhz 160-320hfe $0.34

AWR-101: Q6 2SA720 -19v series reg
512-KSA1220AYS to-126 ecb 120/a160 1.2a 20w 155mhz 35-320hfe $0.39 (R=60-120, O=100/200, Y=160/320)

AWR-101: Q10 2SC869 +5.4 darl driver
512-KSC2383YBU to-92L ecb 160v 1a .9w 50mhz 160-320hfe $0.17

AWR-101: ZD1 / D11 wz-140 14v 1/2 watt zener diode
512-1N5244B Fairchild 14 V, 0.5W Zener

AWR-101: ZD2 / D12 wz-130 13v 1/2 watt zener diode
512-1N5243B Fairchild 13 V, 0.5W Zener
 
Dang, I liked your theory, but ZD1 is not at fault. I'd already replaced it. Pulled just now to test and it's fine.

I've already replaced all the transistors on this board. My subs were the same as yours except for Q6, where I used KSA1013 (you spec'd KSA1220AYS). I've just gone through and double checked the pinouts. Nothing obviously wrong there, unless the silkscreen is bogus.

Could the silkscreen be bogus?

:headscrat
 
I have made the mistake before by mistakenly flip-flopping ZD1 & ZD2, and had similar results with weird power supply readings. Make sure you have the right zeners in the right placement. You also need to check every transistor you replaced, something is not right in that power supply.
 
I have made the mistake before by mistakenly flip-flopping ZD1 & ZD2, and had similar results with weird power supply readings. Make sure you have the right zeners in the right placement. You also need to check every transistor you replaced, something is not right in that power supply.

This is what's killing me. I've checked the transistor pinouts, re-replaced the zeners (they were NTE crap from my LES, so I wanted them out of there anyway) checked or replaced diodes, checked cap polarities. I'm almost certain I've done something bone-stupid, but I'll be damned if I can find it.

Unless somebody has a better idea, I'm going with the "pull/test parts, then replace more carefully until a culprit is found or unit mysteriously works" method.

Here we go...

transistors (diode test)
Q1 OK
Q2 OK
Q3 OK
Q4 OK
Q5 OK
Q7 OK
Q8 OK
Q9 OK
Q10 OK

...
 
Something's got that regulator throttled way down. Check for backwards capacitors C16 maybe, shorted c14 would work through R21
review the below.
IF no progress (all transistors in ok), POST ecb voltages for EVERY transistor.

getting some ground rules/basic assumptions out into the open:

get the data sheet for the replacement transistor from the seller (mouser, download it although my data includes pinout.,

Use the symbol silk screened onto the board.

These are your two guideposts.

every Mouser transistor has a data sheet available for download.... download them and look them up. then install as per the symbol printed on the pc board at that location.
never ever use the original transistor to determine how the replacement will go in.

from an earlier post:



First you need to learn about what the three transistor leads are about, and identifying which is which and where it goes according to the symbol. Then you will see that my parts list include lead arrangements - which assume the transistor lettering (and flat) are facing you and the leads are facing down, then go left to right.

Q13 2sc938 150v 0.05a 0.6w
512-KSC2383YTA to-92L ecb 160v 1a .9w 50mhz 160-320hfe $0.17


attachment.php


The big TO-220's with the metal mounting plate are hard to reverse, but the smaller ones are, but my specified replacements are usually E C B as a rule of thumb BUT we ALWAYS CHECK...

But you really should start here and follow ALL the links...

http://www.audiokarma.org/forums/showthread.php?t=331932&page=5

here's a preview, DO YOU SEE these symbols on the boards you are working on?:


80px-BJT_PNP_symbol.svg.png


80px-BJT_NPN_symbol.svg.png


e is always the arrow on one angled line (direction can be out (npn) or in (pnp) towards the base)
b is always the flat line the other two lines come out if at an angle
c is always the angled line without the arrow

letters can be smudged or illegible, while the symbols are hard to mistake and pretty language independent
pioneer doesn't use letters, if there is a symbol. sometimes in a linear hole arrangement, there is only an 'e'.... with no room for a symbol.



attachment.php



-----------------------------------------------------

now a quick lesson on installing a small transistor in a traditional triangular hole arrangement with a symbol printed in the center of the triangle

1. find the LEFTmost lead on the package and identify it's designation (emitter? base? collector?)
2. look at the symbol on the board, find the corresponding hole
3. insert that lead into that hole
4. find the RIGHTmost lead on the package and identify it's designation (emitter? base? collector?)
5. look at the symbol on the board, find the corresponding hole
6. insert that lead into that hole
7. the center lead will now need to bent forward or back to go into the leftover hole.

DON'T THINK "WHERE IS THE FLAT FACING"
think
"outside leads" and THEIR holes...

this one's ecb....
attachment.php


and two transistor layouts, ebc and ecb with the same triangular target hole arrangement
attachment.php
well, you do need to get the parts, first.... :D

and when ordering the transistors, mouser has links to the transistor's data sheets, DOWNLOAD the data sheets!!! THEY are your BEST guide as to the correct lead connections for THAT particular transistor.

Do you understand the transistor symbol? enough to identify the emitter, base and collector from it? Because most boards (Pioneer) have the symbol printed on it, with holes around it, and it is orientated so there is an emitter hole, a base hole and a collector hole. And obviously, only the transistor's emitter goes into the emitter hole, the base into the base's hole and the collector into the collector's hole. IF you want it to work... :D

oh, and by the way, the symbol usually DOESN'T have the E, C and B letters ON on it... :stupid:
there are two flavors,
pnp: arrow pointing in, 2sa,2sb, ksa, ksb part number prefixes
npn: arrow pointing out, 2sc,2sd,ksc,ksd part number prefixes

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hint: if "rotating" it in your mind is a puzzler, orient it in the hole this way(transistor hole arrangements are usually triangular):

choose the leftmost lead, use the data sheet to identify it... for example it is the emitter
put it in the emitter hole

choose the rightmost lead, use the data sheet to identify it... for example it is the base
find the base hole, rotate the transistor line of leads around the inserted leftmost lead to point at the base hole
put the rightmost (base) lead in the base hole.

the THIRD hole is now either in front of or behind the transistor, in this example the collector is "left over"
bend the center lead forward or back to go into the hole.

easy...

notice that this example had the lead order of emitter, collector, base which is a common lead arrangement

that means that:

looking at the transistor, with the leads pointing DOWN, and the flat part (or lettering in the case of some zetex transistors) FACING YOU
going from left to right has the lead order of emitter, collector, base


attachment.php
 
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