2215A repair and restoration

satbeginner
 

Hi all,

I recently got a (very?) sick 2215A from the well known ePay site.
It came to me perfectly packed from Germany (Thank you for that!) , and was as described and as it was shown in the pictures:

A few scratches on the outside, it powered on, showing a about 6mm trace on the right side of the middle of the screen.
Vertical positioning is working as it should, horizontal position does nothing.
The little piece of trace does follow the timebase settings.
Furthermore there were like 5 knob-caps missing, and the Var Hold Off potmeter axle was broken, and the two front legs are missing.

Using another scope ( a Tek ofcourse!! ) I found that none of the signals around U760 (the horizontal (Pre-) amplifier were correct.
Also, X-Y mode was not working, vertical OK, Horizontal nothing.
To narrow it down further, I removed plug P9705 from the A4 Timing Board where U760 is located, and carefully temporarily bend aside pins 2 and 3 to isolate the Timing board signals from the Main board.
These two pins are the (left of centre and right of centre) signals into the horizontal HV (100V) deflection amplifiers on the main board, now I powered the scope back on:

Right, now I got a perfectly aligned spot exactly in the middle of the screen :-) which I consider good.

To further eliminate possible causes of the problem, I now fed a low (0 - 5V) DC voltage with a 10kOhm series resistor into the two horizontal HV amplifiers (one at the time),
and yes, the dot would move to right and left, according to the input I used and the voltage I applied, and vertical position was working too.
My conclusion so far: the deflection HV amplifiers and the CRT are all OK.

Did I already mentioned the inside of this scope is like new, but I mean, no dust or dirt at all, everything is just spotless.

Anyway, back to the repair.

With the outputs of the U760 still disconnected, I checked the inputs of U760, and they were all still wrong, so I suspect this IC is dead.... (155-0124-00)

I managed to find this IC at Qservice in Greece, not the IC alone, but I found this IC (155-0124-00) is also used in a 455, a SC503, SC504, 2336 and a 2337.
The individual IC was not available at their site, so I ordered a SC503 timing board from them that is sold as tested OK, and has this IC in a socket :-)
In preparation I removed my A4 Timing board, removed the IC U760 and put a socket in myself, so when it arrives, it should be a fairly easy placement.

I also removed the broken Var Hold Off potmeter, and here is were I was a bit disappointed about how Tek put this scope together: removing the front panel from this scope is an utter horrible task!!

The potmeter is a 311-2147-00 (5kOhm, through hole 3mm, half flat axle) Qservice also had one of these so I ordered it with it them too.
Wait and see how this will fit, because the one from the 2215A is a full plastic potmeter, and the one shown in the picture is metal and has thread to mount it, but it looks the same, it also has the very same partnumber.

With respect to the missing knobs: I still have a few of these snap-on knobs (also used on my favorite 24xx scopes) but I ordered some with them too, you just never know, and to get the free shipping ofcourse ;-)

To be continued,

un saludo,

Leo

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