Tek 2215 oscilloscope with A18 preregulator board repair

[Zo-lee]

I recently bought this Tek 2215 on Ebay for AUD120 (including postage). “For parts or repair”. I decided to repair

This is my very first scope. I always wanted one for some faint reason and now I only have to make it working and play with it.

It looked very clean inside and out, far better than I expected.

Of course, I turned it on first and nothing, then checked the fuse with continuity test it was ok.

I opened up the “sucka” and didn’t see or smell anything suspicious for the first sight. As I followed the way I find the A18 preregulator board physically but didn’t find the schematic in the service manual.
It took several days for me to find it in the MANUAL CHANGE INFORMATION at the far end. If it is obvious for you probably you lot smarter than me, good on you.
 
Hopefully you can see too the burn marks around the Q933 transistor’s terminals on the photo . It was quite easy to find.

As I was unscrewing the board I heard something fell to the main board but I needed to disconnect 4 cables first to free the board. I needed some time to find a little white plastic square covered with heat paste (342-0582-00 insulator) down on the main board. On the other side of the A18 I found the Q933 (IRF820) attached to a brown boxy thing (343-1025-00 retainer) and a green something hanging on a wire also cover by the heat paste (still can’t find out what the hell it is, probably the shield)
   
The A18 is upside down now on the photo No2.  I found out the order of the parts: retainer is the closest to A18 board, holding the IRF820 covered by heat paste then the insulator probably glued to the shield (or something?) heat paste again and the whole sandwich screwed to the chassis (red arrow ) This is a pain in the arse design. As I assembled I had to make a long thin hook to hold the shield in position while tighten the screw. Lucky I’m an alien with three hands.

As far as I know they found another solution for the 2215A.

OK, so I de-soldered the transistor and cleaned the board bla-bla and I faced another problem: you (or maybe just me) can’t adjust the transistor in to the holder (brown boxy retainer) after soldered it to the board, you must put these two together first and adjust the transistor’s legs carefully to their holes on the board, keep them in position and start the soldering. Unfortunately I don’t have four hands so I had to find out how. See on photo No3
     
Beautiful.

I also replaced some caps, just for fun and the fuse as well because it blown off on a mysterious way during the process.

I hope there is someone out there who will find this helpful.

Cheers