Dolby A 361 - Testing, Calibrating?

[jensenmann]

There ware quite some revisions of CAT22 cards. You´d have to tell us which revision your faulty card is. But I doubt that all these layouts are floating around. When I was repairing my 361 I couldn´t find much informations other than the manual.
Maybe it´s easier to trace the signal from the meter back into the card. These cards a full of tantalum caps. It´s quite likely that one of them is defective. C501 is the output cap of the meter driver, start there (see manual).

 

[Dr_J]

Hi Jens,

thanks a lot. I'll see what i can do...
It's a Rev. 6, 1973.

ROCK-ON!

 

[Dr_J]

Hi,

i'm moving slowly forward .
I did some A/B comparisons with my oscilloscope, although checked voltages.
At test point 63 on my dead meter driver i read 18Vdc instead of 10.5 (manual) and 12.1 of the working unit.
Although the component test shows a different  pictures when testing Q581 emitter to base.
(The tantalum cap C581 looks fine)
So, my suspect is Q581!

I've got 2 schematics. On one there is no Spezifikation for Q581, on the other i can't read it. It says something like "2N?J??02... 
(The transistor has an id "ST 62430  7 5 2" on it)
On both schematics is a global comment "All PNP equivalent to BC416LC".

Can anybody please help me what kind of transistor i should get for replacement?

THANXS!!!

P.S.:
Just checked one of my working cards, rev #7.
I'll think on this Q581 is a 2SA970 (GR 2H)...

 

[JohnRoberts]

doesn't look like it needs anything special

Try any general purpose PNP you have laying around.

JR

 

[Dr_J]

Hey John,

THANKS A LOT!!

Luckily i found a BC558B laying around...  ;D
After de-soldering the old one, i tested it with the scope. To me it looked dead...

Then i put the BC558B in (different pinout) and switched the unit ON...
... voltage at the meter amplifier was still 10.8Vdc... shock!! 
... but after a while it dropped down to 7.something...
... then to 0.18 and after another while to 0.06 - which is fine!

I don't know what was going on in this box...???
But currently it looks good, needle is dancing  (hope it will last...)

THANKS AGAIN &
ROCK-ON!

 

[user 37518]

https://www.ebay.com/itm/Used-Dolby-Level-Meter-For-363-And-Other-Models-Complete-Tested-Works-ME/324098413314?hash=item4b75c55302:g:6zwAAOSwOM5eZszU

Thats David Kulka from studio electronics in Burbank CA