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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

satbeginner
 

Correction: it was not the Var Hold Off potmeter that was broken, but the B-Trigger potmeter, I wish it would have been the Var Hold Off, that one is easy to replace.....

To be continued,

Un saludo,

Leo

satbeginner
 

Hello all,

an update on the repair of my 2215A:

I received the SC-503 horizontal board and the 5 kOhm potmeter from Qservice in Greece, perfectly packed and quickly shipped as always :-)

I double checked the parts and voltages around the 155-0124-00 Horizontal amplifier IC before putting it back in, but after it was put in, I had my traces back!
I call that success, but........

Did you ever heard of "Leo's Law #3" ??

Well, "Leo's law number three" states that when you're dealing with a "nice" malfunction, there will ALWAYS be another thing broken too, and again, also with this little 2215A

Yes, the traces were back, the time base is working, all good, but, it would not trigger on Ch1 nor on Ch2...
Line trigger is perfect and external trigger is perfect, but Internal trigger is just non existent.

It took me some time to check all voltages and signals around U310, U335 and most important, U350, but I concluded it was the U350 that was dead, or at least very sick.
Using my Chinese vacuum desolder tool I was able to remove the IC without removing the main-board, and when testing the 5 individual transistors in the CA3127E it turned out that the transistors A, B and C were dead.
Both transistors D and E were still OK, so my guess is, some high Voltage came into the external trigger input and found it's way into U350??

Anyway, none of the regular shops like Mouser or others still have these on stock, so I ordered some in China, and to be sure, some of the CA3102E (U310 and U335) too.

So, to be continued,

Un saludo,

Leo

satbeginner
 

The proof of the pudding is in the eating :-)

Quick and dirty check to see if a replacement CA3127E will fix the triggering.
Since the chip is out, the 16 dip holes are open and easily accessible front the bottom side...

So I temporarily out some general purpose NPN transistors and, and behold: it is working.
So now I can calmly wait for the IC to arrive.

Here some pictures of the "temporary fix"

https://groups.io/g/TekScopes/album?id=242324

Un saludo,

Leo

satbeginner
 

Hi all,

while waiting for the slow boat from China, I decided to add cooling to my 2215A.

There have been lengthy discussions about whether it is, or not is necessary, but since I am planning to keep this scope as my run-around scope I decided to add it anyway.
The cabinet has the holes, the main circuit board is prepared for it, the silkscreen at the bottom even has the markings, so this is what I did: (like it's done in other 22xx scopes)

Added
CR 965 (1N4007)
R965 (2,7Ohm 1/4W)
C965 (2200uF 25V)
P9965 (2 pin molex slotted connector)
Fan 60mm x 60mm x 15mm 12VDC 0,16A

Less than € 3 in parts, so why not?

Again, a picture can be found here: https://groups.io/g/TekScopes/album?id=242324


Un saludo,

Leo

satbeginner
 

Still waiting for the slowest boat ever!

The transistor chips are still not here...

To be continued,

Un saludo,

Leo