Help Needed: need replacements for 2SA912, 2SC1914, 2SC1885 on a Pioneer

[Cosmic_S]

Hello, like the title says i am trying to fix a intermittently unstable Pioneer SA-3000 amp for good, it has one of the following issues at one time or all together: random popping and crackling from speakers even with volume closed and no signal being fed (like a very very dirty record), erratic relay behavior, has burned drivers and its resistors several times, took out one output one time.

currently i am debating whether to replace both 2SA798 with two matched KSA992s in an adapter pcb i am designing currently, or just glue one next to the other side y side and heatshrinked together. or even use a single SMD part (tho the ones ive found as per datasheet are labeled as "general purpose" while the 992s are labeled as audio parts)

anyway i need replacements for:

(Q9) 2SC1914
(Q11) 2SC1885 (tall type)
(Q13) 2SA912 (tall type)

(i belive its called TO-92L ?) and i am afraid using regular 92s because i dont know if they will run hotter than designed

i dont know exactly if they are bad or not, ive already replaced all outputs and all drivers and it worked fine the day i fixed it, the next day after being left alone the crackling popping came back along with erratic relay behavior (bias was fine tho for some reason)

this amp has been repaired by another tech 6-7 times in the last 4-5 years always the same failure mode and symptoms.
so id like to fix this amp once and for all (this will be my 2nd attempt) by shotgunning all remaining transistors in the amp pcb on both channels

As always any help is greatly appreciated

(ive attached part of the schematic with the transistors to be replaced pointed out)

 

[ivandezande]

A “tech” repaired it 6-7 times? You really brought it back after time number 3 and thought “oh yeah, he’ll fix it this time”???

KSC1845
KSC2383
KSA1013

I’d be replacing the 798 with two KSA992’s as well, they don’t need to be glued/heatshrunk, whatever. Just solder the emitter legs together and put it in.

 

[Cosmic_S]

A “tech” repaired it 6-7 times? You really brought it back after time number 3 and thought “oh yeah, he’ll fix it this time”???

KSC1845
KSC2383
KSA1013

I’d be replacing the 798 with two KSA992’s as well, they don’t need to be glued/heatshrunk, whatever. Just solder the emitter legs together and put it in.

this amp is my father's so ive no choice on who he choose and brought it to fix it in the past, and afaik he bought the amp broken already so who knows how many times more has it been worked on.

anyway yeah, the 798s are gonna be gone even if the other transistors are fine, i just thought of shotgunning the rest just in case just because of the constant instability, might work today, may or may not tomorrow, may work for a few weeks or months until it doesnt

about the 1013, i still dont know much about choosing parts myself (ive sucessfully repaired 2 other amps in the past by reading and asking around for modern replacements to use), so the 1013 looking at the datasheet it says for color tvs and its only 50mhz ? ive already replaced the drivers with TTA004B and TTC004B which are 100mhz and outputs with 15032 and 15033 on both channels, and these being the ones before them wouldnt they cause instability by being slower than the originals ? (some sources say 75mhz others 150mhz)

 

[ivandezande]

this amp is my father's so ive no choice on who he choose and brought it to fix it in the past, and afaik he bought the amp broken already so who knows how many times more has it been worked on.

anyway yeah, the 798s are gonna be gone even if the other transistors are fine, i just thought of shotgunning the rest just in case just because of the constant instability, might work today, may or may not tomorrow, may work for a few weeks or months until it doesnt

about the 1013, i still dont know much about choosing parts myself (ive sucessfully repaired 2 other amps in the past by reading and asking around for modern replacements to use), so the 1013 looking at the datasheet it says for color tvs and its only 50mhz ? ive already replaced the drivers with TTA004B and TTC004B which are 100mhz and outputs with 15032 and 15033 on both channels, and these being the ones before them wouldnt they cause instability by being slower than the originals ? (some sources say 75mhz others 150mhz)

It will be fine, and that’s the correct replacement.