Pioneer SA-7800 - Help replacing transistors!

[groenhen]

I'm in no rush, really-really.
I will go with Mark & wait for his instructions.
Uncle Nick (Nicholas) lives in another city in fact. Rarely comes to visit us (now I think he was "motivated" by SA7800). So, I can only ask his advice by phone... Internet is something he doesn't like much... close to zero (he's so stubborn like a mule).
Regards,
Stanley

 

[jheu02]

If he's not too far away, why not arrange to take the amp and parts when they come in and do it as a project together...you doing the physical work and he talking to you about how best to go about it or at least double checking you're getting things in correctly.

 

[larryderouin]

Good idea. It sounds like he's very interested in it and possibly enough that he'd kibbutz on it. Sound him out on it.

Larry

 

[groenhen]

He's very weak (heart problems). Few weeks ago he had a crisis, we called the ambulance and they took him to hospital.
Now he's ok (sort of) but doctor said he must rest and we don't want to stress him...
That's why I need your help and I count on Mark. I also have two guys at HW/service department, who can do soldering, drilling, mounting, cleaning, lubing, etc.
I will "stress" uncle Nick only if I get stuck, only if necessary.
Anyway, I'll tell him... he would be impressed people saying nice words about him on AK
Thank you!

 

[groenhen]

I noticed two transistors in the power supply 2SD712 and 2SB682 (if I'm not mistaken), they HAVE heat-sinks, at least for this model I have ... (In SA708 for example they dont have heatsinks ).
Yet, 2SA913 and 2SC1913 in the power amp section, they don't have heatsinks. Why, they do not run hot?... so Pioneer considered it's not necessary to cool them?

Some people use heatsinks even if it;s not really required... others simply skip this aspect and bake transistors (eventually killing them).

 

[markthefixer]

I have said it time after time, it depends upon the circuit and how it is being used.

THEN it depends upon bad engineering. The presence of an unneeded heat sink is RARELY a bad thing.

I'm slightly surprised that they, the drivers for the outputs, DON'T have them.

 

[groenhen]

...The presence of an unneeded heat sink is RARELY a bad thing. I'm slightly surprised that they, the drivers for the outputs, DON'T have them.

I've been ill for some days, a terrible flu (or something), I'm still dizzy, but now I am much better.
Back on rails/topic now: Uncle Nick said "old transistors are not necessarily bad-transistors, but as a retirement gift, you can give them a heat-sink!".
So, they'll be reused as some "active retired transistors"... I guess?!
IMHO new components/parts are by far better than 35yo ones.
BTW, Mark, Larry : Uncle N seems more & more interested about AK forum! :thmbsp:

 

[larryderouin]

Good to hear about Uncle Nick. I too have Heart problems from age 30 (now 59) 2 bypass surgeries, 35+ angioplasties, 18 stents over the years. Hobbies are good physical and occupational therapy as long as you don't overdo it. Psychologically he'll feel better doing something that interests him. Which leads to him improving physically.

Don't push him, but let him find his limits. He'll find out what he's capable of and can improve in some areas. The worst thing is to tell him he can't do something. Independence is a strong feeling among us "older" guys who are physically disabled to an extent. We want to be able to do things we did 10-20-30 years ago, but we can't do them the same way, so we improvise, adapt, overcome!

Like one of the guys said earlier, take the amp and the parts over and ask him what he thinks about this, that, or the other. If you're not comfortable with how a part goes in ask him about it and why one way and not another (there's 6 ways for a transistor to go in the holes, but only one is RIGHT!).

The big bonus here is you spending time with him and learning the in's and out's of this stuff. And he is passing on to another generation what he learned. Getting the amp fixed is a side bonus. Go at his pace.

 

[groenhen]

Ok, starting with 9 or 10 of August I'll be on holiday, so I'll have plenty of time to spend on SA-7800 restoration.
I'll try to go to my uncle Nick, so he can supervise the process closely.
But it's Mark who will guide me and decide what and how to do all things...

BTW, I can't keep myself from sharing this:
- I showed uncle Nick some solder(ing) I did and he said: "Wow, I start getting headaches!... Son, you surely have two left hands!"...
So I'm a miracle, right?
Now, honestly, I wasn't doing such a bad job, but he is so picky, always so censorious... And he has a terrible sense of humor!

Best regards,
Stanley.

 

[larryderouin]

Stanley;

Remember that Left Handed people are in their Right Minds. (I know, bad joke, but true.) And according to Uncle Nick, you got a double dose.

Practice. Soldering is a skill set that has to be used consistently to get and stay proficient. Don't let Uncle discourage you. There's the fact that he's most likely ACTUALLY PROUD OF YOU, Like's your work, but has a hard time with telling you that. Keep it up tho, give him something to look forward to. Good therapy, for both of you.

Larry

 

[Kahoona]

Best I can do for advice is this. I have been in your situation. Listen to Markthefixer. Focus on where and what he tells you. Understand that there are other causes that made this happen and if not found you will be starting over. Dependable parts come from Mouser. I also found that when MTF gives a parts list he puts a lot of time into it so I just get everything on the list. When he says test I often simply replace after all it those parts are soo cheap really. Don't forget the mica insulators and conductive paste for any transistors you change or test.
You will learn a lot doing this and get a sense of satisfaction that you could not have gotten if it worked when you got it. You will also get better sound and reliability. Have fun!

 

[groenhen]

You will learn a lot doing this and get a sense of satisfaction that you could not have gotten if it worked when you got it. You will also get better sound and reliability. Have fun!

To be honest, that's why I bought this amplifier in the first place.
I knew it had issues with one channel...

Anyway, thank you for your kind advices!
Wow, AK forum is full of wonderful people... I only had this feeling on avrfreaks dot net, where I am/was a senior member. Now I moved (forward) to ARM STM32, yet my hearth still beats for those 8 bit AVRs

Another personal "satisfaction" is the fact that I managed to get a closer/better relation with my uncle Nick... We are sharing the same passion for electronics, yet I think we have lost so many many years not realizing that! What a pity, I can't turn back time! Sigh...

One question about (mica) insulators: Are they absolutely necessary? I mean, should I use insulator even if the heat-sink comes in contact <only> with that particular transistor? (please excuse my poor English).

 

[markthefixer]

If there were insulators originally, yes.

NOT having insulators is a cheap-out move. A big waving short circuit waiting to happen.

 

[markthefixer]

I have not forgotten you, I worked on the transistors and the amp board parts all weekend (instead of posting in other threads).

I got the relay and the trim pots as well as the diodes, and was rechecking the transistors after the sun came up this morning when I found a fault, thus I need sleep before I continue proofing my post-able list.

which resistors are burned up and not yet replaced? plus capacitors just occurred to me... sigh....

 

[groenhen]

...which resistors are burned up and not yet replaced? ...

Sorry for the late reply...
Our company has been taken over (I think this is the term/expression) by an Austrian company/holding. So, it has been a terrible mess at the office in the last week. Not sure how good or bad this change will be for me :scratch2:.

Well, about the resistor(s): only R33 (560 ohm) is scorched and not yet replaced.
In fact, in this amp I replaced only two resistors (burned up): 150 ohm/0,5Watt for R57 and R59 (took 'em from uncle Nick, but if you think I should buy from mouser... better quality?).
When you said "wait, don't mess with the board", I stopped "drilling" on the board and just doing some "cosmetic" work on the amp.

Many thanks for all the help (time, effort). I will do my best not to disappoint you

 

[groenhen]

I got the relay and the trim pots as well as the diodes,

Ooops... relay too?!? Even if it works fine?
Uncle N. shares your opinion about the relay, saying that after 35 yrs the relay internal contacts must be worn out... Is this the reason for replacing it?
As replacement he suggested something with transparent case... Why? Is it so important to see the "guts&bowels" of that relay? :scratch2:

 

[cirtcele]

Hey Markthefixer did you compile the transistor replacement list? I have been watching to see what you recommend as replacements for the 2sa913 and the 2sc1913, but this thread has not had any activity for awhile.

 

[markthefixer]

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.

 

[groenhen]

Hi Mark, hi everybody!

Thanks for the list.
At first view: I see no replacement for 2SA1075 and 2SC2525...

Idea is I will make only one order to Mouser as shipment to EU is quite expensive.
If possible, of course... sigh.

I have here somewhere a list for capacitors.
Probably I will manage to find it (on my office PC or on my PC at home).

What about R33 (560 ohm) ...?
R57 and R59 I've already replaced them. Bad idea?

Best regards
I will resume my work on SA7800 during the next days...

 

[groenhen]

E-CAPACITORS LIST (managed to find it)
Feel free to comment, any idea is welcome !!!

– on Power Amplifier Assembly (GWH-118)

CEANL R22M 50  0,22uF / 50V
Low Leakage C21, C22
Mouser: 667-ECQ-V1H224JL3

CEA 331P 6  330uF / 6V C25
Mouser: 647-UKL1A331KPDANA

CEA 101P 50  100uF / 50V C26
Mouser: 647-UKL1H101KPD

– on Power Supply (GWR-12)

CEA 2R2P 50  2,2uF / 50V C28
Mouser: 647-UPW1H2R2MDD

CEA 221P 80  220uF / 80V C29, C30
Mouser: 647-UPW2A221MHD

CEA 101P 10  100uF / 10V C33
Mouser: 647-UPW1A101MDD

CEANL 4R7M 50  4,7uF / 50V
Low Leakage C34, C35
Mouser: 647-UKL1H4R7MDD1AA

CEA 470P 63  47uF / 63V C36, C37
Mouser: 647-UPW1J470MPD

ACH-082  8000uF / 50V C39 – C42
Mouser: 647-LGY1H822MELB40

>>>.