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Pioneer SA-7800 - Help replacing transistors!

Ahhh, I believe there is a lot of controversy whether or not to solder those wire wrappings! Haha

Yes I will be recapping this amp and the entire works. This is mostly just out of curiosity to see how good I can get this thing working. The physical condition is pretty good but I need a new speaker selector switch (broke off while being shipped to me)
 
Meesterstech said:
Ahhh, I believe there is a lot of controversy whether or not to solder those wire wrappings! Haha
Click to expand...

I did solder ALL wire wrappings for a Pioneer SA-708 that was completely dead (it just went bananas all of a sudden, no sound at all...).
Now it works great, no more contact failures anymore :)
BTW: I always like to remove the wrappings & use connectors for the display board(s).

... The physical condition is pretty good but I need a new speaker selector switch (broke off while being shipped to me)
Click to expand...
ASB-102 -> Try e-bay. I see such things there from time to time.
Or: http://parts.pioneerelectronics.com
 
Thanks, I have been searching for a few months now. Still haven't had any luck finding one!

These amps seem to be pretty rare at the moment. Oh, and I think I will try cleaning up all the wire wrappings.
 
Yikes $30 for shipping. I don't think I can justify that! I'll have to think about it, but it looks like they have a replacement.

Thanks
 
pacparts takes orders they can't deliver on, and in a few weeks they refund any money.

That rotary speaker select switch asb-102 will come from a donor unit, unfortunately...

according to:
http://parts.pioneerelectronics.com/part.asp?productNum=ASB-102

sa-7800, sa-8800, sa-9800 only donors.

Unfortunately, being on a corner, that switch takes a beating.

Now, most importantly, BACK to those RCA output transistors:

UNTIL you find the Ft speed spec for those transistors, you DO NOT KNOW!!!!!!!!!!!!!!! grrrrrrrrrrrrrrrrrrrr!!!!!!!!!!!!!

They HAVE to be high speed for the NSA to work, otherwise the distortion figures will be at least 15 times higher if not more.
Just using slower DRIVERS took the distortion a magnitude higher.

And, unless specified, the Ft of a power transistor is usually in the 4 mhz range - woefully inadequate for the NSA design.
 
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ok, I found it, it's 20mhz... still not good enough...

because:
20 to original 60 mhz???
but
20mhz to 30mhz....
hmmm, would have to hang a distortion analyzer on the channels to see how badly they are affected...
 
markthefixer said:
Most of those type relays have transparent cases now.

sa-7800 Power amp GWH-118 GWH118 all repair transistors list - but not necessarily a recommendation for replacement.

q1,q2 2sa979 dual 100v 50ma .2w 250-800hfe
q3 q4 2sc2291 dual 100v 100ma .2w 100mhz 250-1200hfe
leave these dual transistors alone.
individual a992 and c1845's would be used.


q31 2sa733 60v .1a .25w 180mhz 200hfe
q13 q14 q15 q16 2sa750 50v 50ma .25w 130mhz 450hfe
q19 q20 2sa872a 120v 50ma .3w 120mhz 250-800hfe
q27 q28 2sa1914 90v 50ma .2w 150mhz 250-1200hfe
512-KSA992FBU (ln)to-92 ecb 120v .05a .5w 100mhz 150-800hfe $0.05 ea

q5 q6 2sa912 150v 100ma .75w 200mhz
512-KSA1220AYS to-126 ecb 120/a160 1.2a 1.2w/20w 175mhz 35-320hfe $0.39 (R=60-120, O=100/200, Y=160/320)


q29 q30 2sc945 60v .1a .25w 150mhz 90-600hfe
q11 q12 q17 q18 2sc1400 100v 50ma .25w 100mhz 500hfe
q7 q8 q21 q22 2sc1775 90v 50ma .3w 200m 400-1200hfe
512-KSC1845EBU (ln)to-92 ecb 120v .05a .5w 100mhz 150-800hfe $0.05 ea

q9 q10 2sc1885 150v 50ma .75w 200mhz 150hfe
512-KSC2690AYS to-126 ecb 120/a160 1.2a 1.2w/20w 175mhz 35-320hfe $0.40



q25 q26 2sa913 to-220 150v 1.5a 15w 65-330hfe 120mhz
757-2SA1930(Q,M) pnp to-220 bce 180v 2a 20w 200mhz 50-320hfe 200mhz nsa driver


q23 q24 2sc1913 to-220 150v 1.5a 15w 65-330hfe 120mhz
757-2SC5171(Q,M) npn to-220 bce 180v 2a 20w 200mhz 50-320hfe 200mhz nsa driver

q32 2sc945 60v .1a .25w 150mhz 90-600hfe timing capacitor discharge transistor
512-KSC2383YTA to-92L ecb 160v 1a .9w 50mhz 160-320hfe $0.17


q33 2sc1384 50v 1.5a 1w 200mhz relay coil driver.
512-KSC2690AYS to-126 ecb 120/a160 1.2a 1.2w/20w 175mhz 35-320hfe $0.40



d1 - 6, 9-16 1s2076 replace: 512-1N4454 fast 100v .2a
d7 d8 stv2h
d17-20 d23 1s2471 replace: 512-1N4454 75v .2a
d21 d22 d24 (prot) 1s2472 55v replace 512-1n4148

d25 mz-130:
512-1N5243B Fairchild 13 V, 0.5W Zener
or
78-BZX55B13 vishay 13 V, 0.5w 2% zener

relay: asr-052 4pdt 24 volts pcb mount 653-MY4-02-DC24



sa-7800 Power amp GWH118

And maybe now you will start listening to me about that upside down GWF-115 phono amplifier board, and it's high power class A output that overheats the Q5, Q6 2sa912 transistor, which I replaced with 512-KSA1220AYS to-126 ecb 120/a160 1.2a 1.2w/20w 175mhz 35-320hfe $0.39 (R=60-120, O=100/200, Y=160/320)
and stuck a small heat sink on them. I will show pictures where I reversed the high power dissipation resistors to the other side of the board (heat rises, where I expect it to be soaked up by a metal shield plate, and not cook the other components in a lower and cooler zone.
Click to expand...
This is a interesting post!
I've currently started working on a Realistic SA-500 with a static- ridden right channel(after it warms up).
I have a feeling besides solder joints, it has bad drivers. Going to test all of them along with the associated resistors, diodes, and treat both channels to a refresh.
Thanks Mark for your excellent input.
 
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