Pioneer SX-780 no sound from one channel

zebulon1 said:
2SC1775: 512-KSC1845FTA
2sa912: 512-KSA1220AYS
Click to expand...

zeb, transistor recommendations??? :no:


gwk-118 q11 2sc1775 vas darl dvr 512-KSC1845FTA
gwk-118 q12 2sc1775 vas darl dvr 512-KSC1845FTA
gwk-118 q13 2sc1885 vas darl pass 3ma 38v 0.11W 512-KSC2383YTA
gwk-118 q14 2sc1885 vas darl pass 3ma 38v 0.11W 512-KSC2383YTA
gwk-118 q15 2sa912 current source 3mA 38v 0.11W 512-KSA1013YBU
gwk-118 q16 2sa912 current source 3mA 38v 0.11W 512-KSA1013YBU

how'd I get it?

39.5 - 39.2 / 100 (R261) = 3mA
3mA x 38 volts = 0.114W

vas = voltage amplifier stage, using a darlington pair (driver and pass)
darlington driver needs gain
darlington pass transistor handles power

current source is base biased to give a base voltage 0.6v higher than the emitter voltage.
it is set up for (39.5 - 38.6) = 0.9v at the base, giving (39.5 - 39.2) = 0.3v at the emitter, and since a 100 ohm resistor was used, that's 3mA.
dropping 38v to get 3mA dissipates 0.114 watts of power - well within the capability of a TO-92L package.
double it for worst case output voltage swing.
still OK.
 
Last edited:
Thank you very much !

Thank you very much. Appreciate all the help. I think I will order (10) of each. Hate it when I have to wait a week for parts.
Anything while I'm in there and placing and order that I should get to have on hand?

Was also wondering If those .220 emitter resistors are anything special ( the rectangle ceramic looking ones?
I may want to stock a couple of those critters.
I cant seem to be able to convert Transistors at Mouser, even when I take off the 2S in front of Numbers. was wanting to get the Q19, Q20, and Q25 ordered also.
I think they are
2SD325R =Q19
2SB536L = Q20
2SD712? = Q25 not sure on this one?
 
Last edited:
I like to hit e'm with the big guns. Inexperience at work> :D
Thanks for explaining part of the dirty secret.
 
2SD325R =Q19 NPN power
2SD712? = Q25 NPN power

2SB536L = Q20 PNP power



PNP power: 512-KSA940TU pnp to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.62
NPN power: 512-KSC2073TU npn to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.66

or for complete overkill (they handle high temperatures better - which means bigger eat sinks instead):

PNP power: 863-MJE15033G pnp to-220 bce 250v 8a 50w 30mhz 70hfe
NPN power: 863-MJE15032G npn to-220 bce 250v 8a 50w 30mhz 70hfe

q26 2sc1384 : 512-KSC2690AYS to-126 ecb 120/a160 1.2a 1.2w/20w 175mhz 35-320hfe $0.40

Q7, Q8 2sa726: 512-KSA992FBU (ln)to-92 ecb 120v .05a .5w 100mhz 300-600hfe $0.17 ea

The resistors are slightly more problematic, the best source for the flat square type is eBay - there are a few American sellers, and a lot of Pacific rim sellers.
0.22 ohms 2 watts although 5 watts is fine. In fact the dual resistors line up with holes in the pc board. Your choice.
don't want wire wound - I am suspicious of inductance concerns. WHY did they use the more expensive non-inductive plate type resistors if they didn't have to?

here's a "backup" metal Oxide resistor 0.22 ohms 2 watts 5% mouser number: 660-MOSX2CT52RR22J about $0.13 ea...
 
Last edited:
thank you

Thanks a bunch.

are those .220 ohm emitter rectangular resistors different from regular resistors? Don't know that wattage?
I have some .220 emitter resistors that are not rectangular in shape and are new. Wondered if they were usable.
 
you can try them - old ones were 2 watt and non inductive "plate" resistors.

but don't know if freqs on this type of amp can go high enough to matter.

on other (NSA) amps they can - the drivers are 100-200 mhz and outputs 60mhz and that is prime inductive territory.
 
Dual resistors?

markthefixer said:
2SD325R =Q19 NPN power
2SD712? = Q25 NPN power

2SB536L = Q20 PNP power



PNP power: 512-KSA940TU pnp to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.62
NPN power: 512-KSC2073TU npn to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.66

or for complete overkill (they handle high temperatures better - which means bigger eat sinks instead):

PNP power: 863-MJE15033G pnp to-220 bce 250v 8a 50w 30mhz 70hfe
NPN power: 863-MJE15032G npn to-220 bce 250v 8a 50w 30mhz 70hfe

q26 2sc1384 : 512-KSC2690AYS to-126 ecb 120/a160 1.2a 1.2w/20w 175mhz 35-320hfe $0.40

Q7, Q8 2sa726: 512-KSA992FBU (ln)to-92 ecb 120v .05a .5w 100mhz 300-600hfe $0.17 ea

The resistors are slightly more problematic, the best source for the flat square type is eBay - there are a few American sellers, and a lot of Pacific rim sellers.
0.22 ohms 2 watts although 5 watts is fine. In fact the dual resistors line up with holes in the pc board. Your choice.
don't want wire wound - I am suspicious of inductance concerns. WHY did they use the more expensive non-inductive plate type resistors if they didn't have to?

here's a "backup" metal Oxide resistor 0.22 ohms 2 watts 5% mouser number: 660-MOSX2CT52RR22J about $0.13 ea...
Click to expand...

Is Dual resistors the brand for the ones that line up with the holes nicely?
 
don't see any rectangle or square style resistors out there that are not wire wound and cast ceramic, guessing I may have purchased wire wound ones. 5 watt and .22 ohm.
I do see that they are non-inductive.
 
Should have the new Diodes and transistors in from mouser this afternoon and hopefully get them installed by Monday.
 
damn, there's a huge post of mine MISSING from this thread, about those transistors and resistors... what the heck HAPPENED to it???


Which ones did you get?
a979, c2291 DO NOT get replaced - they are unavailable .period. they are dual pnp and dual npn transistors. c1384 has 2 different functions, which one are you talking about? because thne two differnt functions dictate two different replacements.

not k3496 just plain k34 also unavailable (they don't MAKE 50v jfets anymore!!) and has different replacements for the muting ones or the power supply constant current hum rejectors.
 
let me see what I got

let me see what came from Mouser and E-bay. Been bust on wife's kitchen and haven't got back to SX-780 yet. maybe be working on it on Wednesday
 
strader61 said:
I'm not sure that the R258 is right. What I mean is I'm testing the one that's in schematic and that was suggested, but I don't think it is the one we are really wanting to test? here's what I have. Maybe you can show me in the photos that I've attached? appears I've been testing the ones with the white cloth wrap covering them.

R261=100

R259=151.25

R262=100.00

R258=2.223 and appears to be red, red, red, gold in color
Click to expand...
R-259 and r-260 in my SX-780 are 150 ohm resistors schematic calls for 200 ohms so Pioneer made some changes somewhere along the line.R-259 was fried and the relay doesn't latch.Replaced r-259 and no luck replaced Q11,Q13,Q15 R259 still gets real hot so its drawing to much current from somewhere?
 
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