Technics SA-828 - Static with audio, then stopped working

[73's de Edd]

.


Sires . . . . . . .

Those mighty-mites look just fine to me . . . . just disregard the voluminous shadows that the pins are casting.

That VERY SPECIFIC, very small case profile defines that item directly to the Matsushita product line.

I don't possibly think that I have ever seen them replicated with that distinctive notch out at the top of the case.
Usually you just bring solder up to the original 3 . . . time onset oxidized . . . . solder connections to get a melding of the old and new solders and reflow of the two solders.
And then rapidly walk the soldering iron tip between the three melted joints and the transistor will fall right down to a hand held underneath the board.
I have only seen slightly smaller cases in the Sony family of small signal "digital" transistors, that additionally contain deposited resistor pairs internally.

My only variant, would have been to mark all of my pulled right channel transistors with a dot of Red fingernail polish . . .RED for Right . . . .in case they get shuffled around later on.



73's de Edd


.

 

[darryl603]

.


Sires . . . . . . .

Those mighty-mites look just fine to me . . . . just disregard the voluminous shadows that the pins are casting.

That VERY SPECIFIC, very small case profile defines that item directly to the Matsushita product line.

I don't possibly think that I have ever seen them replicated with that distinctive notch out at the top of the case.
Usually you just bring solder up to the original 3 . . . time onset oxidized . . . . solder connections to get a melding of the old and new solders and reflow of the two solders.
And then rapidly walk the soldering iron tip between the three melted joints and the transistor will fall right down to a hand held underneath the board.
I have only seen slightly smaller cases in the Sony family of small signal "digital" transistors, that additionally contain deposited resistor pairs internally.

My only variant, would have been to mark all of my pulled right channel transistors with a dot of Red fingernail polish . . .RED for Right . . . .in case they get shuffled around later on.



73's de Edd


.

Hi, 73s best regards.
Have you had a chance to look at the voltages I listed above? If so, are they out of whack or what would be the next step to home in on why I have no output?

 

[Alexandre Freddi]

Hi, did you yank those out with a pry bar?

Sorry but I didn't follow you.May I help you with some information I got during the repair of my 828? Best regards

 

[darryl603]

Okay, sounds good...
.
.

 

[darryl603]

Please measure the DC voltages relative to chaises GND on IC1002 (TA7317 ) it is a SIP 9 pin device.
And both sides of D1001 relative to chaises GND .

D1001 + 38.1 v - 39.4 v
IC1002

1. .648 v
2. -.737 v
3. 0
4. 0
5. -347 mv
6. 37.8 v
7. 0
8. -27.7 mv
9. 2.84 v

 

[dorke]

The reading of -39.4v @D1001 is strange can you verify it ?

The conditions show your AMP is in protection mode(pin6=37.8V.)
Is the protection LED on the front panel(top left side) "on"?

Please measure the DC voltage on the center pins of Z601 and Z602.

Pin 8 voltage is not fine, please re-measure it .
Take a good look at C109 and R1049 for visible problems, measure them(without power to the unit).

 

[darryl603]

Hi,
I measured d1001 and got anode 38.43 and cathode 39.75
Pin 8 on IC1002 was -26.8 mV
Z601 0 V
Z602 -63.8 V
R1049 148.7
C1009 37uf

The amp is definitely in protection mode and yes, the red light is lit for safety. The display appears to be working fine.

 

[dorke]

Z601 voltage is fine.
Z602 voltage at fault , and the reason the amp is in protection.
That means the right channel is faulty.

With volume at minimum.
Please measure DC voltages relative to chassis GND on:
anode of D608 and Cathode of D610 .
anode and cathode of D616 .
anode and cathode of D622 .

With the amp powered down.
Please measure on IC1002 resistance( ohm not diode):
1. between pins 8 and 9.
2. between pins 8 and 7.

 

[darryl603]

Okay, here goes:
IC1002
pins 8, 9 147.6 ohms
pins 7, 8 OL

D608 -.393
D610 -65.6V
D616 an -63.3 V ca -65.1 V
D622 an -64.9 V ca -65.2 V

 

[dorke]

1. Resistance between pins 8,9 of IC1002 is too low, should be about 150K.

2. Q628 and D616 may be bad

3. Please check DC voltages relative to chassis GND on both sides of:
R664,R672.

4. Please check DC voltages relative to chassis GND on Q622.

5. After that please check with power-down, in-circuit(don't pull out of PCB) in diode test mode:
Q628 and D616.

 

[darryl603]

I'm sorry. I re checked 8,9 and read 148k and 7,8 was about 15 M ohms

Q622 was -B -63.6, C -63.2 E -63.6
D616 1.135 .259

Q628
BE .638
BC ..612
EB 1.3
CB .612
CE 1.4

 

[dorke]

D608 Anode = -0.393 (from #248) and Q622(C)= -63.2(from #250),are in miss-agreement.
Being the same point,they should be the same voltage.
Which voltage is it?

Please re-measure voltages relative to chassis GND on Q622.
Please re-measure voltages relative to chassis GND on both sides of:
D608,D610,D618,D622.

and add both sides of
D606,D612,D614,D616,D616

 

[darryl603]

while I was probing around there with the stereo on, it suddenly came out of protection mode. But it wasn't good out of the speaker terminals. Basically, it squealed and cut back into protect again. When I cut the speaker output off at the front panel, it came out of protect mode again. The volume is down all the way. I tested q622 after that happened and base and emitter were almost even at - 65.3 but collector read -64.5 V Prior to that, they were still where I had reported in the previous post. I'm keeping the speaker output off and it seems to pass the relay every time I turn it on. I don't want to hurt anything though. After I shut it off, I felt around on the bottom of the board and nothig felt too hot so, that's good... The meter was connected to the base of Q622

 

[dorke]

Well,
Are you saying that if you disable the speakers from the front panel,the amp isn't in protection mode?

Could you please complete the tests of #251.
Please test voltages( relative to GND )on both sides of R634,R644 and R664,R672.

 

[darryl603]

Yes, that's correct.
R 634 64.3 64.1

 

[dorke]

Do you have speakers connected to the unit?
What is the voltage at center pin of Z602 when you enable/disable the speakers from the panel and the amp goes in/out of protection?

 

[darryl603]

The right side had - 62 v dc and the left side had + 62 v dc
Enabling or disabling the speakers had no effect at all.
What do you make of that???

 

[dorke]

Confusing.
So now the enabling/disabling of the speakers has no effect on protection or not?

 

[darryl603]

Yeah, very weird. At first, when the relay first came on, I went to plug in a speaker on the left side and I saw a spark. So, obviously I didn't do that again lol

 

[dorke]

That spark could mean your speaker is blown.
Check it's resistance.


But to carry on with the amp we need the measurements of #251 and #253.
All tests should be done with no speakers connected and volume at minimum.