[SOLVED] Tektronix 2213 preregulator fail

Hello everybody

I`m trying to repair my old Tek2213 preregulator (A18) board. I dont know why but the switch transistor Q933 had all pins in short circuit...
I replaced Q933 and Q931 (due the E&C are short circuit).

The problem is that I didnt find any literature (service manual, forums) where the exact transistor type was depicted, I only find that it could be an 2N2907. I replaced the original one by this but... now when I switch on the ORC, it try to turn on in severals time (like a loop) but it doesn't. I hear a sound like a little bird in the preregulator (severals time).
If I unplug the P804&P803 (circuit load from A18) the preregulator turn on successully and I dont hear the sound

1-Anybody can tell me the exact Q931 type?
2-This sound is due an electrolytic C failure?

Thanks in advance

Hi,
In the Serv Man(REV NOV 1981), page 8-26 is to see (Q915 & 931 are the same type):
A18Q931 151-0164-00 ΧΒ020100 TRANSISTOR :SILICON, PNP 01295 SKB3334.
**broken link removed**
I hope, it helps?
K.

Thanks Karesz

Indeed the SKB3334 is the original part, but its hard to purchase (outside USA)
With the NSN I found in
https://www.sphere.bc.ca/test/tek-parts/tekparts2.html
that the SKB3334 could be an A5T2907, again its not easy to purchase, so seemingly it could be MPS2907/2N2907, but (always be a but) the Fairchild 2N2907 (CBE) has a different pin out from Motorla MPS2907 (EBC), so really with this information I dont know if 2N2907 is a replace for SKB3334

Ill do some test and post the results, if the prergulator wont put on fire...

Hi,
your welcome!
I dont believe, that a mirrored pinout can be a real problem, then you can bend the base pin in the opposit direction...
Other question is with parameter equivalent, but in a pwr supply it can be (hopfely)not so very critical.
These Scope is in public relative bad documented; I downloaded some time ago from somewhere a 14MB ServMan, but i.e. exactly your preregulator schema is missed, it has a PCB population drowing, parts lits at the beginning, than is finished. :-(
Maybe you can have more success in the "yahoo Tek-group"?: **broken link removed**
Good progress!
K.

Finally the preregulator is working fine.

Q931 (SKB3334) can be replaced by 2N2907 from SGSThomson ( TO-18 )
The Q931 pin out match with the depicted at figure 9.2 (CBE) in the Service Manual revNOV82.

The sound like a bird on each turn on, still is there (I belive that is CR909) but ... the law says:
"if everythings work fine, dont touch"

I draw the A18 schematics, when I ll scan it, I ll post it

Hi Generico,
Fine!
I will wait (too) for your scan_& tnx yet...
Best reagards!
K.

Finally, these attachments are the 2213 preregulator schematics
Have fun