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SA-9800 Frys Speakers!

ehc68

ehc68

My SX-1050
Shortly after buying this amp (around 18 years ago) one of the channels (can't remember which one) started to become weak and amp started distorting.....then fried a pretty nice set of Technics speakers. It had been
sitting in storage ever since.

First of all...the protection relay engages as normal (or at least it did until the probe of my multimeter slipped.....read on).

The meter on the front panel of amp lights unevenly and will not light up at all
if the switch is set to "dim".
Right and left channel of the amps fluroscan display peak at 10.

The DC offset was:
Right channel - Bounces between -190.0mv to -210.0mv range.
Left channel - Same thing....-190.0mv and -210.0mv

Pins.....
1) -16.2v
2) -16.2v
3) 6.4v
4) 6.4v
5) 5.2v
6) 5.2v
7) 3.2v
8) 0 (black ground wire)
9) -78.0v
10) This is where it all happened. My meter probe slipped and shorted pins 10 and 11. When this happened, a CHUNK of plastic blew from a transistor (2SK34) located at Q5 and looked like there was smoke coming from some other part of the power supply board....maybe from what looks like to me a resistor (it has an insulation covering it). I didn't get a real good look because I quickly and frantically killed the power. It connects to pin 32.....illustrated in the pic). Before that happend, this would get really hot....too hot to touch.
After that, I wasn't about to turn it back on again to continue collecting the voltages until I checked in here first to see what to do for fear something else was going to fry. Take a look at the pic......
 

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I feel for you, this is what you should never be without and never ever use bare probes in a P/S
 

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Twenty20Man said:
I feel for you, this is what you should never be without and never ever use bare probes in a P/S
Click to expand...

Yeah, and I feel like an idiot for not at LEAST wrapping the probe with electric tape.:tears:
I wonder if Radio Shack carry those covers.:scratch2:
 
Oh boy... :tears:

Turn it on momentarily and check the voltages on pins 13 and 15.

They are the main supply voltages of +68v (13) and -68 (15).

Also check ALL the fuses (with the power off) by removing them and checking them with an ohmmeter.

Looks like mouser is going to get an EXTENSIVE order.

You'll probably be doing a lot of desoldering and testing of transistors out of circuit, but DON'T jump the gun, because we may have popped fuses, or rectifiers.... the presence of voltages at those pins (13,15) will tell the tale...

edit:
The bright side is that the negative regulator side (Q2,Q4,Q6,Q8,Q10,Q12) is a tracking regulator (R7,R6,R9), and the destruction on the positive side deprived the negative side of it's reference voltage and so the negative side is just shut down.. I HOPE !!!!! depends upon where that probe went.... 10 and 11 are at -32, while 12 is a 150 ohm resistor to the RAW + 68 volt POWER... a rather insensitive place.... why Q5 LITERALLY went BALLISTIC however..... <hmmmm....>
 
Well, I went ahead and turned it back on and it's not smoking any longer.
I insulated the meter probe (all but the tip, of course) and re-tested DC voltages at pins 1 through 13. Here's what it reads now.......

1) -6.3
2) -6.3
3) .5
4) .5
5) -.2
6) -.1
7) -.1
8) 0 (ground)
9) -81.3
10) -1.3
11) -1.3
12) 80.0
13) 80.0

DC Offset is:
Right channel - 5.0V (OL reading in mv range)
Left channel - 4.0v (OL reading in mv range)
 
ehc68 said:
Well, I went ahead and turned it back on and it's not smoking any longer.
I insulated the meter probe (all but the tip, of course) and re-tested DC voltages at pins 1 through 13. Here's what it reads now.......

1) -6.3
2) -6.3
3) .5
4) .5
5) -.2
6) -.1
7) -.1
8) 0 (ground)
9) -81.3
10) -1.3
11) -1.3
12) 80.0
13) 80.0

DC Offset is:
Right channel - 5.0V (OL reading in mv range)
Left channel - 4.0v (OL reading in mv range)
Click to expand...

Offset is immaterial until the power supply voltages are correct.

You did test the fuses? and WHAT is PIN 15's VOLTAGE ?? I can INFER and ASSUME from the pin 9 reading... but doing that can make trouble... especially in THIS situation.

markthefixer said:
Turn it on momentarily and check the voltages on pins 13 and 15.

They are the main supply voltages of +68v (13) and -68 (15).

Also check ALL the fuses (with the power off) by removing them and checking them with an ohmmeter.
Click to expand...

edit:
The +80 on 12 & 13 means that the positive supply is NOT drawing any current.
So use EchoWar's transistor test OUT of circuit on Q1, Q3, Q7, Q9 & Q11. WHEN YOU REMOVE THEM, MAKE DRAWINGS OF EACH's ORIENTATION, so later on we can more easily find the E, B & C connections for each...

You DID download the manual??????? That should give you the lead layouts on the transistor's cases...
 
markthefixer said:
use EchoWar's transistor test OUT of circuit on Q1, Q3, Q7, Q9 & Q11. WHEN YOU REMOVE THEM, MAKE DRAWINGS OF EACH's ORIENTATION, so later on we can more easily find the E, B & C connections for each...
Click to expand...

Ok...I'll try to take close up pictures of the transistors on the board as well as drawings just to be sure. Then I'll remove Q1, Q3, Q7, Q9 & Q11.

markthefixer said:
You DID download the manual??????? That should give you the lead layouts on the transistor's cases...
Click to expand...

Yes, I sure did.

I also checked the fuses and they both read 0 Ohms.

I'll start on this tomorrow and I'll let you know the results of the tests on Q1, Q3, Q7, Q9 & Q11.
 
Hello, that power supply board is really the worst part of the SA-9800, I wish you good luck! I wonder if you can find a working replacement for the 2SK34 FET, please let us know.

Helmut
 
Ok, here's what I have.....

With nothing connected to the meter probes, the meter reads 3209mv.

Q1 (2sc1735 - NPN) -

Positive on base, negative on emitter - Nothing (no drop)

Positive on base, negative on collector - 624mv

Negative on base, positive on emitter - Nothing (no drop)

Negative on base, positive on collector - 3202mv (little drop)

Positive on collector, negative on emitter - Nothing (no drop)

Q3 (2sa733 - PNP) -

Negative on base, positive on emitter - 023mv (continuity)

Negative on base, positive on collector - 870mv

Positive on base, negative on emitter - 023mv (continuity)

Positive on base, negative on collector - 1011mv

Negative on collector, positive on emitter - 1007mv

Q7 (2sc1914 - NPN) -

Positive on base, negative on emitter - 081mv (continuity)

Positive on base, negative on collector - 076mv (continuity)

Negative on base, positive on emitter - 082mv (continuity)

Negative on base, positive on collector - 077mv (continuity)

Positive on collector, negative on emitter - 007mv (continuity)

Q9 (2sc945 - NPN)

Positive on base, negative on emitter - 689mv

Positive on base, negative on collector - 684mv

Negative on base, positive on emitter - Nothing (no drop)

Negative on base, positive on collector - Nothing (no drop)

Positive on collector, negative on emitter - Nothing (no drop)

Q11 (2sd712 - NPN)

Positive on base, negative on emitter - 600mv

Positive on base, negative on collector - 595mv

Negative on base, positive on emitter - Nothing (no drop)

Negative on base, positive on collector - Nothing (no drop)

Positive on collector, negative on emitter - Nothing (no drop)
 
Q1, Q3, Q7 look dead, Q9, Q11 look ok, as I somewhat expected.

I'm looking for suitable transistor replacements.


Q1 will probably be ZTX694b and Q3 will probably be ztx795a... the ratings are a bit high, and they are pricey, but they should survive. they are well regarded here... but not in exactly this type of application.

Q5 is problematic since it is a 50v jfet...

Q7 again will probably be ztx 694b

the zetexes are rated at 140 volts, 0.5 amps, 1.5 watts and an Ft of 100 MHz.

Since the raw LOADED dc is 68 volts and unloaded due to fault will be higher.

I am investigating the circuit to see if a 30v fet will suffice.

I am also getting some wacky 2sk34 cross references... including mosfets... and I am considering why not use a mosfet (if mods would be needed.... I need to look VERY close..)
 
I found a place that carry replacements for Q1, Q3, and Q7 at http://www.bdent.com/
They are all REALLY cheap, but there is $15.00 minimum and it
doesn't look like I'll need enough parts to meet that amount.
They, of course, didn't have the 2sk34.
 
OK...Acme Enterprises NO minimum order!!!
They have Q1 at least....I'll have to look and see if they have the others.
I'll be back online a little later.
 
acme huh, and no minimun, (no minimun "penalty" like digikey?) I'll have to check them out.
edit: oh yeah!! that's where I get my sony repair parts!!!

specs for the 2sc1919 :
npn si 90v, 50mA, .2w, 150 MHz Ft, hfe 250 to 1200

data book subs I was investigating include:
2sc1841, 2sc1890, 2sc2240, 2sc2363, 2sc2389, 2sc3495, 2sd756 and 2sd 1011.m
 
Well, whatever happened, my last BRILLIANT post was just LOST!!!!!!

I HATE having to do this over......... here's the bare bones...


the ORIGINAL was npn 90v 0.05a .2w 150 mhz ft 250-1200 hfe

the nte31 is npn 160v 1a .9w 100 MHZ ft 100-200 hfe @ $3.36 each at mouser

the ztx694B npn 120v .5a 1.5w 130 mhz 150-500 hfe @ $1.09 each at mouser

the zetex has more gain and the nte runs the risk of being counterfeit.
The gain may not be as important in a power supply circuit. BUT the increased current of the nte31 ISN'T needed and it costs us gain.

NTE is ALWAYS the LAST resort ....
 
Excellent!! I will order the ztx694B along with the others payday.
I don't have a clue what happened to our posts. I think the AK server
was down for a little bit. I wasn't able to access this page until just a few minutes ago.

As always, thank you very much Mark for your help!!


One other question.....do you think this is going to solve my original issues
with this amp, or is this just going to correct what I messed up when my meter probe slipped and bring me back to the original complaint?
 
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