Technics SA-828 Receiver from 70s- Is it worth trying to save this aging patient?

[73's de Edd]

.


Sir darryl603

Good show ! . . . . . . on the successful burn in time . . . . .

. . . .

Considering that I am not misreading Q706 for Q708 on a blurry small schematic page.
Q708 is the series pass transistor of a 12 supply which later subdivides to a 5V supply and a mere cursory look
seems to reveal they feed the mild demands of a display.
How do the 5 voltage specs given around that area compare to your unit.
If electrolytic caps C719 and C720 have appreciably declined in capacitance both R717 and Q708 will run warmer than normal.

My 8 separate pages of schematics don't include a parts list, so what is the 2S number of that Q708 and I just might assume it might be in a TO-220 casing and might also justify a small heat sink being used with it ?

73's de Edd

 

[dorke]

Welcome back,
Please measure the voltages on Q708 and Q710 relative to GND.

Can you quantify "pretty hot" in degrees ?

 

[darryl603]

Hey guys,
Here are the readings I got from Q707 and Q708:
Incidentally, after about 10 seconds, you really don't want to leave your finger on Q708.

Q707:
D 24.7
G 19.3
S 5.6

Q708:
B 14.3
C 24.7
E 13.7

I have a picture of the parts I replaced to get the receiver working again. I have some time Sunday, so I'll check back to see what you think.Thanks and see you later...

 

[darryl603]

.


Sir darryl603

Good show ! . . . . . . on the successful burn in time . . . . .

. . . .

Considering that I am not misreading Q706 for Q708 on a blurry small schematic page.
Q708 is the series pass transistor of a 12 supply which later subdivides to a 5V supply and a mere cursory look
seems to reveal they feed the mild demands of a display.
How do the 5 voltage specs given around that area compare to your unit.
If electrolytic caps C719 and C720 have appreciably declined in capacitance both R717 and Q708 will run warmer than normal.

My 8 separate pages of schematics don't include a parts list, so what is the 2S number of that Q708 and I just might assume it might be in a TO-220 casing and might also justify a small heat sink being used with it ?

73's de Edd

What's your e mail? I can send you what I have, if you want?

 

[darryl603]

Q 710

B 5.60
C 12.35
E 5.01

 

[dorke]

Voltages are a bit of.
and Q707 is wrong (it has 2 pins tied together)
Could you please re- check all with (volume at minimum) and add Q709 as well.

 

[darryl603]

Q 709

B 14.2
C 14.2
E 5.58

 

[dorke]

Well,
Q709 is also wrong Vb=Vc ?

Take the time to measure the above voltages (Q707 up to Q710) in the same conditions:
1.same GND reference for the (-)probe.
2.Volume at minimum.

 

[Iceman from McMurdo]

For "dorke" and "73s de Edd" - Sorry I've been off the net for so long, but some other priorities popped up and I had to let the hobby repair work slip a bit... Sorry.

Hoping to get back at it right after the holidays, but wanted to let you know I have NOT given up yet, and will still be needing your help to get my SA-828 running again (if you can bear with me a bit longer)!

Biggest problem to date has been identifying the correct replacement parts - primarily the "matching" pairs. Asked DigiKey for some techie help, but OEM parts are no longer avail and many of the substitute parts they recommended either had different specs or were from different manufacturers. Each time I'd contact them for verification I'd seem to get different recommendations, so I'm still not sure what parts to order...

The attachment contains the latest list I'm trying to work from (matching pairs are last 3) ... Happy to hear any suggestions if anyone has any. Thanks!