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Pioneer SA-7800 - Help replacing transistors!

Nice neat work on the transistor wiring. :thmbsp:

re: 3,4,5 on indicator board - do the specialized status indicators in the tube indicate tape, phono tuner, aux?

pin 3 is supposedly involved in that. but the switch seems to be tied to ground, not that 15v.

Pioneer does have manual errors. we've caught plenty.
 
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markthefixer said:
Nice neat work on the transistor wiring. :thmbsp:
Click to expand...
I'm glad you like it!
Nobody noticed I did a trick with the STV diode?! :)

re: 3,4,5 on indicator board - do the specialized status indicators in the tube indicate tape, phono tuner, aux?

pin 3 is supposedly involved in that. but the switch seems to be tied to ground, not that 15v.
Click to expand...
Well, as far as I can see things, the pin allocation seems to be like that:
- pin 3 = supplies 15V to GWF-115 board (phono/tuner/aux selector & tape sw)
- pin 4 = +45V power supply
- pin 5 = GND.
I'm not 100% sure, I will check that on Monday, using a multimeter...
Now i'm at home with a terrible flu, while the amp is at the office... waiting for the compressed air blower.

================================================================
Hey Mark, what do you think about the values of the (measured) DC offset:
- 14 mV on LEFT channel
- 24 mV on RIGHT
Are those figures ok?
Can/should I get them closer to ZERO?... If yes, how?
TIA, Stanley.
 
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Good enough. risk versus reward... There IS NO offset adjustment on it...

to do so, you gotta build a circuit like found on the sa-9800.

A "base current stealer"...

STV diode trick? You mean the force spreader washer on the stv diodes' mount?

My standard practice...

There's a bajillion things I do to any particular unit.... all different depending upon circumstances....
 
markthefixer said:
Good enough. risk versus reward... There IS NO offset adjustment on it...

to do so, you gotta build a circuit like found on the sa-9800.

A "base current stealer"...
Click to expand...

Yeah, I've already seen the service manual of big(gest) brother (SA-9800)...
Well, if you say those values are good enough, then it's ok :)
So, just to have a reference:
What is the maximum acceptable value for the DC offset?

I will not modify the existing design/schematics...
The only thing I modified was the pilot lamp circuit, i.e. I did a LED conversion.
Oh, and I removed a capacitor that was kinda weird put there instead of a jumper! (on the PS board - as seen on one of my previous posts)
 
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groenhen said:
Well, as far as I can see things, the pin allocation seems to be like that:
- pin 3 = supplies 15V to GWF-115 board (phono/tuner/aux selector & tape sw)
- pin 4 = +45V power supply
- pin 5 = GND.
I'm not 100% sure, I will check that on Monday, using a multimeter...
Click to expand...

Sorry for the late reply... I was very ill, still recovering :(
I did the above measurements and now I can confirm:
- pin 3 = +15.1 V
- pin 4 = +41.2 V
- pin 5 = GND.

So, the idea is: follow the schematic diagram in the service manual (page 19), NOT the connection diagram (from page 20).
I will come back with some pictures when I'll feel better...
BR,
Stanley.

EDIT:
Ok, only one pic... camera ran out of battery.
 

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Off topic: Never got a flu like this before... :( More than a week and I'm still sick...

Anyway, I finally managed to put all the pieces together, i.e. I re-assembled the unit (see pic).
I'm not 100% happy, because the top right corner of the front panel is a bit nicked :(
That's life... Bad luck, I didn't have the chance to have it all ok because the previous owner was too stupid to wrap & pack the amp as it should.
He just put the amp in a carton box and added some rags. The carrier did the rest!

Well, bad luck strikes again... my CD player doesn't play anymore :(
It is a Vieta VH-CD030, by chance anyone know this brand?
I searched the AK forums but didn't find anything relevant about it.
I would surely like to fix this CD player instead of buying a new one...

Finally I want to express my gratitude to all the people on this forum who helped me, especially to: Mark, Lee, rcs16 (Rick?), Larry.
My wish came true: I got this amp working before Christmas! Unfortunately the CD player went bananas...

[EDIT]
I forgot to mention:
- all pots and switches were cleaned and lubed;
- that orange power-lamp light looks just great! :) ( BTW: The LED related resistors are cold as ice ! )
 

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Hi,
Reviving this old thread...

Uncle Nick came to visit us... He brought me some Wima film capacitors for the FL-display board that is not recapped yet :)
- two pcs. 1uF/50V
- three pcs. 2.2uF/50V.
I hope they'll fit... (Mouser -> MKS0B041000F00KSSD)

I've just had a conversation with uncle Nick about my amp restoration...
He said he usually avoids Nichicons(!?) and he rather prefers Panasonic capacitors (both e-caps and film)!

So, as I already used Nichicons in my amps, I would like to ask you:
-> Are Panasonic capacitors better than Nichicons ?

BR, Stanley.
 
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Personal choice / prejudice. Maybe decades ago there was a difference, but that's all sorted out now.

EchoWars has always mentioned Nichicon PW and HE caps in the same sentence as the Panasonic FC and FM.

They are ALL high quality, long life, general purpose electrolytic caps.

When you see "low esr" caps - those are more for switching power supplies where significant heat is developed by the cap's internal resistance. Their lives are much shorter, at temperature.
 
Mark, one question...
I'm planning to recap the FL-display board (AWV-001), with uncle Nick's help, i.e. he is willing to provide all e-caps...
Only one problem : for C9 -> CEA 470P 10 , Nick has (in stock) only 47uF/25V Panasonic FC-series (his favorite)...
Should I use that as replacement or I should find an e-cap rated at EXACTLY 10Volts ?
TIA, Stanley.
 
I agree with mark, there are so many different models from each mfg. Both are quality mfg's as well.
Pan FC are probably better quality than original, which were one of a number of Japanese mfg's.
You are fine with 10-16-25V, but you have to check for fit, can diameter, lead pitch, lead diam, there is a bit of variation, but it comes down to, form, fit, function.
 
rcs16 said:
...
Pan FC are probably better quality than original, which were one of a number of Japanese mfg's.
You are fine with 10-16-25V, but you have to check for fit, can diameter, lead pitch, lead diam, there is a bit of variation, but it comes down to, form, fit, function.
Click to expand...

Well, even if the service manual says "C9 -> CEA 470P 10", what I see on board seems to be 47uF/16V made by ... Nichicon JAPAN :)

Obsolete manual?
Pioneer factory didn't have the 10v flavor at hand?
Or maybe Pioneer considered 16v is somehow safer (10v e-cap being too LOW for that position) ?

Off topic:
Uncle Nick just fixed my CD player, so now I can use my SA-7800 amp to listen to some good music (Spanish guitar).
 
So my outputs (2SA1075 & 2SC2525) were replaced with RCA's. Would the ON SEMI you used be better quality? I'm changing everything I can, if the ON Semi's are better I will swap them out.
 
863-MJL1302AG pnp TO-264 bce 250V 15/30A 200W 30mhz 45-150hfe $3.57 ea
863-MJL3281AG npn TO-264 bce 250V 15/30A 200W 30mhz 45-150hfe $3.57 ea


check the spec's on the RCA's they used, or post the numbers and we'll find them.
The 2sa1075 etc was a unique - ring emitter transistor...


the originals were:
120v 12a 120w 60-200hfe (min 45mhz, typ 60mhz) Ft and needed the speed.
 
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I used On-Semi because that's what I had at hand at that moment...
I wish I could have been able to use Sankens but it wasn't that easy... long story...

Ok, from the data-sheet you posted it seems your output transistors are just fine.
So, are you having problems with the sound quality your amp currently delivers or what?

BR, Stanley.

BTW: I still have those Sankens (2 x 2SA1216G + 2 x 2SC2922G ) new & originals, if anyone is interested (PM me).
 
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Oh no these outputs are working fine. Since I'm replacing almost all the transistors I wondered if it would be a good idea to put new outputs in. Looks like I'll just leave them alone
 
Meesterstech said:
Oh no these outputs are working fine. Since I'm replacing almost all the transistors I wondered if it would be a good idea to put new outputs in. Looks like I'll just leave them alone
Click to expand...

Yup, leave those outputs in place...

Don't know what exactly your amp condition is, yet I suggest recapping would be a good idea, if e-caps are too old.
Also try to clean and lube all the pots and switches.
If you notice oxidation around wrappings, try to clean those wrappings and moreover, solder them to ensure proper contact.
 
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