SX-828 main amp AWH010 question

[Japetus]

Dear Ak'ers,

I'm currently refurbishing my SX828, it has had no issues.

I just want to enhance future reliability (power supply, protection) and do some modding by the usual adding/replacing of those old 'lytic caps with stacked poly film caps for the entire audio signal path (head amp, AF-unit, ....).
All boards except tuner and amp are finished.

Currently I'm about to start with the main amp board. The transistors in question are encircled (see pic). They are:
Q9, Q10: 2SC484 TO-5
Q11, Q12: 2SA484 TO-5
All other transistors will be replaced anyway.

IF, then I'd replace Q9 to Q12 with SC2073TU (SC484) resp. SA940TU (SA484), all TO-220.

The question:
I do not know if the originals are prone to failure or not. Especially since each has this large surfaced heatsinks failure doesn't seem to be likely to me, but I have no expert knowledge and may be wrong here.

Could anybody more knowledgable give a recommendation if a replacement would be reasonable?

Frank

 

[markthefixer]

Yes, I've done a few sx-828's and replacing all the transistors in the amp is both reasonable and yields fantastic results

the new transistors are MUCH better than the originals

use heatsinks on the drivers. 940/2073 to keep them nice and cool!

here's the parts I used:

edit- I'm sorry that I don't have the part numbers for the caps or the trimpots....

input differentials:
2sa572 to-92 bce 50v 0.05a 0.2w 160-960hfe 80MHz Ft
use:
512-KSA992FBU (ln)to-92 ecb 120v .05a .5w 100mhz 150-800hfe $0.05 ea

vas and bias stage:
2sc1124 140v 1a .95w 160hfe 120MHz Ft
use:
512-KSC2690AYS to-126 ecb 120/a160 1.2a 20w 155mhz 35-320hfe $0.40


drivers:
2sa484 to-5 ebc 110v 1.5a 0.8w 30-300hfe 20mhz
2sc484 to-5 ebc 110v 1.5a 0.8w 30-300hfe 20mhz
use:
512-KSA940TU_Q pnp to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.54
512-KSC2073TU npn to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.54


outputs:
2sa680 pnp to-3 120v 12a 100w 40-140hfe 6mhz
2sc1080 npn to-3 120v 12a 100w 40-140hfe 6mhz
use:
534-4662 to-3 mica insulators $0.16 each
863-MJ21193G pnp to-3 250v 16A 250W 4mhz 8-75hfe $3.83
863-MJ21194G npn to-3 250v 16A 250W 4mhz 8-75hfe $3.83

 

[Japetus]

So I'll change them.
No need for saying sorry for not supplying part numbers at all!!

I got all transistors (except outputs) and caps (UKL's, UPW's, ECQ's) already at hand, just need to order suitable heatsinks for the 940's and 2073's (no need to find them for me, I'm fine).

Thanks a lot Mark, again (and as usual I may add :thmbsp!

Frank

 

[Whatever1]

Moved

 

[Japetus]

Finished

Now finally, if and who ever might be planning to do some work on his (or her???) SX828 and is interested in what I did, here it is:

The following list refers to the SX-828 Model FVZW Service Manual here on AK.
All electrolytic caps are Nichicon types if not otherwise noted; almost all parts can be found by mouser via entering parts type, and all Panasonic electrolytics could as well also be Nichicons.

Where I used certain stacked polyester film caps, f. e. ‘MKS’ type, one can as well use any other stacked film cap, f. e. Panasonics ECQ-type or CD (Cornel-Dubiliers) DSF-types.
At certain places I used much higher voltage rated electrolytics ONLY because more suitable values I had not at hand.

I did power supply and protection first and proved that receiver is functional at LEAST soon after any board was finished (otherwise it will KILL YOU if you’re up to search for an error if you did all at once).


Common parts, pg. 20:
original: -> new
designation: type µF/V -> type µF/V of replacement

C5 CEA 220/6 -> Panasonic RAD FC 220/25
C6, C7 ACH 8000/50 -> BCComponents 10000/63 series 050/052 (main filter caps: new ones have less diameter than original, adaptation necessary); each paralleled with an MKS-4 4.7/250 stacked poly film cap
C8 ACH 1000/63 -> UPW 1000/200
C9 CEB 470/16 -> TVX 470/25

D1 SIB01-01 -> 1N4004


Head amp unit W21-002, pg. 35:
C1, C2 CEA 22/10 -> UKL 22/50 + paralleled 1,0/50 stacked poly film cap (preferably Panasonic ECQV (or Cornell-Dubilier DSF))
C3, C4 CEA 4.7/16 -> UKL 4.7/50
C5, C6 CEA 10/25 -> UKL 10/50 + paralleled MKS-2 0.47/63
C15 CEA 220/25 -> UPW 220/50


AF-Unit AWK-012, pg. 37:
C11, C12 CEA 47/6 -> UKL 47/35
C13, C14 CEA 47/50 -> UPW 47/200 (is overkill, but was at hand)
C15, C16 CSSA 1.5/25 -> MKS-4 1.5/50
C25, C26 CSSA 3.3/25 -> UKL 2.2/50 + paralleled 1.0/50 stacked poly film cap
C27, C28 CEA 100/6 -> UPW 100/63 (overkill)
C29, C30 CEA 47/50 -> UPW 47/200
C31, C32 CSSA 2.2/25 -> a bunch of paralleled poly film caps 1.0, 0.68 and 0.56 µF, all rated 100V
C37, C38 CSSA 1.0/25 -> ECQ 1.0/50
C43, C44 CEA 100/25 -> Panasonic RAD FC 100/35
C45, C46 CSSA 3.3/25 -> UKL 2.2/50 + paralleled 1.0/50 stacked poly film cap

Q3, Q4 SA725 -> KSA992FBU
Q5…Q8 SC1312 -> KSC1845UBU (UBU no longer available)


Main amp unit (AWH-010)
C1, C2 CSSA 1/50 -> ECQ 1/50
C5, C6 CEA 22/6 -> UKL 22/50
C9, C10 CEA 220/10 -> UKL 220/50
C11, C12 CEA 100/50 -> UPW 100/63

VR1, VR2 0…4.7 kOhm -> 0…5 kOhm 25-turn var. pot 64Y-5.0K, these are for OFFSET
VR3, VR4 0…100 Ohm -> 0…100 Ohm 25-turn var. pot 64Y-500, these are for BIAS

I measured resistance of desoldered originals and set replacements to these values before soldered them in (kept track of pin orientation).

Q1, Q3 SA572 -> KSA992FBU (two that have a close matching hFe-value, f. e. 740 and 741)
Q2, Q4 SA572 -> KSA992FBU (two that have a close matching hFe-value, may differ slightly from Q1, Q3)
Q5…Q8 SC1121 -> KSC2690AYS
Q9, Q10 SC484 -> KSC2073TU + heatsink V 5801B (heat resistance 27 K/W) + non-conductive thermalcote (nonetheless sink may be electrically alive but does not touch anywhere, enough room in vicinity)
Q11, Q12 SA484 -> KSA940TU + heatsink V 5801B (heat resistance 27 K/W)
Q13, Q14 SC1080 -> MJ15024G OnSemi + TO-3 Mica + non-conductive thermalcote, there MUST NOT BE conductivity to the heatsink
Q15, Q16 SA680 -> MJ15025G OnSemi + TO-3 Mica + non-conductive thermalcote, there MUST NOT BE conductivity to the heatsink


Power Supply AWR-010
C5 CEA 1000/10 -> UPW 1000/35
C6…C9 CEA 100/50 -> UPW 100/63
C10 CEA 220/16 -> Panasonic RAD FC 220/35
C12 CEA 220/35 -> UPW 220/50
C13 CEA 470/16 -> UPW 470/25

R12 MOX 330 Ohm/ 2 W -> metal oxide film 330 Ohm / 2 W

Q1 SD234 -> KSC2073TU
Q2 SC373 -> KSC2383YBU
Q3 SD313 -> KSC2073TU
Q1 and Q3 get a selfmade heatsink (as can easily be noticed...)
D7 WZ130 -> 1N5243


Protection circuit AWM-025-C
(Attention: The manual shows W28-008, but in my SX828 the AWM-025-C can be found. This is the protection board of later production SX838, which is completely different but can be found in the SX838’s manual pg. 48)
C1, C2 CSSA 0.22/10 -> MKS-4 0.22/100
C3, C4 CEA 330/6 -> UPW 330/25
C5 CEA 4.7/25 -> UPW 4.7/50
C6 CEA 100/16 -> UPW 100/25

Q6 SC945 -> KSD1616AGBU
Q7 SC1384 -> KSC2690YSTU

I added the diode ‘D9’ 1N4004 between pin 9 and 10, banded end on pin 10 (to kill shut-off generated voltage hitback on Q7), as always has been recommended by you-know-who


After all work is done:

First run is on DBT for live-of-the-unit-insurance reasons.

Without DBT then bias and offset is addressed:

The bias measuring points for the left channel are pins # 11 (pos lead) and pin # 17 (neg lead).

The bias measuring points for the right channel are pins # 12 (pos lead) and pin # 18 (neg lead).

The BIAS target voltage might be 20 millivolts (0.020 V) as the average guess of some qualified other AK-members here.

Offset voltages can be measured for the left channel on pin 7 to ground and for the right channel on pin 8 to ground.

The OFFSET target voltage is zero volts (0.000 V) with NO SIGNAL.

This is what I did, not necessarily the only or best solution. Errors must be credited to me, almost anything else to EW and/or MTF.

The pics show the finished main amp, the new outputs with the STV4's on the heatsink, the AF-Unit before and after modification.

Frank

 

[SicMan]

Good post Frank .. :thmbsp:

 

[Japetus]

Thanks, John!
This was a lot of work, and I had more troubles with this unit than with others before. But I like the looks of the SX828 very much and wanted to get its innards as good as I can.
Now it's back in our living room and running DVD and TV - improving audio drastically, especially if some sports events take place the atmoshere is delivered real lively.

Frank

 

[djordan]

Now finally, if and who ever might be planning to do some work on his (or her???) SX828 and is interested in what I did, here it is:

* * *
Frank

Frank,

Just reviving this as I might want to pick up an SX-828 locally.
Ballpark, what would you say spent for all these parts?
And how long would you estimate it took you?

I gather this isn't for the in-experienced non-tech...
I probably would ask a qualified tech to do this for me...
(the part about getting KILLED is a bit discouraging)

Thanks for any info you can share about time and expense!

djordan

 

[markthefixer]

As long as it isn't plugged in, and your hands inside, you are ok - worst case you let the smoke out, and we REALLY try to avoid that - questions are welcome - DON'T GUESS - ASK

like we say - there is no such thing as a dumb question - although reading and research of old threads is encouraged. The dumb thing is to guess wrong and damage something.

while I haven't been hand holding repairs lately, there are a lot of held hands on here that can pass the same advice along. Even ADD to it.

 

[Japetus]

Just reviving this as I might want to pick up an SX-828 locally. Ballpark, what would you say spent for all these parts?

Hard to say because there were left-overs, spare sparts and parts for other projects, but (very roughly) could have been 30 to 40 € (spent at mouser in $).

And how long would you estimate it took you?

Also only roughly maybe 20 - 30h. If you're interested in how these things work and you're new, then you'll have fun in finding out, following the traces, soldering components in and so on - this is very time consuming but it's time you gladly spend.
If you just want to have it done and you're experienced enough it takes only a fraction of that.

I gather this isn't for the in-experienced non-tech... I probably would ask a qualified tech to do this for me...
(the part about getting KILLED is a bit discouraging)

That refers only to the length of a possible search for mistakes if you do all at once and it doesn't work. THAT 'd be discouraging...

Mostly all I know about working at these old gems is from Mark or Glen and old threads of them. That's a treasure accessible freely, you only have to make use of it.

But anyway, don't let you be kept away from that SX828. Mine is still working perfectly since.

Frank

 

[riverty]

I thought I'd chime in on this thread and say that I just finished rebuilding the power supply and main amp on a Pioneer SX-828 using information from this, and other threads found here. Many thanks to Mark, Frank, and many others. Cheers!

Attached are before and after pictures of the main amp and a pic of the power supply board.

 

[rcs16]

You left the old pots in there they will probably be okay, if they were cleaned or checked out.

 

[Japetus]

I thought I'd chime in on this thread and say that I just finished rebuilding the power supply and main amp on a Pioneer SX-828 using information from this, and other threads found here. Many thanks to Mark, Frank, and many others. Cheers!

Attached are before and after pictures of the main amp and a pic of the power supply board.

Its nice to read someone found this old thread useful for his purpose. Thanks riverty, for noticing!

All the best,
Frank

 

[riverty]

rcs16, they were cleaned (DeoxIT) and they seemed to work just fine.

And Frank, you bet!

 

[EJR]

Finished

Now finally, if and who ever might be planning to do some work on his (or her???) SX828 and is interested in what I did, here it is:

The following list refers to the SX-828 Model FVZW Service Manual here on AK.
All electrolytic caps are Nichicon types if not otherwise noted; almost all parts can be found by mouser via entering parts type, and all Panasonic electrolytics could as well also be Nichicons.
..........

Incredible work, Frank! I am right now in the middle of upgrading my SX-828. Many folks have and will benefit from all your work. Thanks so much for posting it.