Tektronix 2235 grief

IMHO: gather your friends at the top of a tall building, toss this "scope" as far as it will go.

BFoelsch wrote in news: snipped-for-privacy@4ax.com:

Perhaps a bad solder joint at the pin/substrate interface? Or a fractured SMD cap. I believe regular solder will not work here,but don't have any alternatives,either.Possibly some low-temp stuff like Chip-Quik may work without destroying the metallization on the substrate.

The other alternative is to find a replacement thickfilm. Sphere in Canada may have new parts for this,or cannabalize from a parts scope.

(I always wondered if one could make a small PCB using SMD resistors and caps instead of the ceramic thickfilm,to replace one of these.)

"Ancient_Hacker" wrote in news: snipped-for-privacy@p79g2000cwp.googlegroups.com:

Bad advice;the 2235 was a good scope.

Well, opinions will vary. In my somewhat limited (about 6) experience:

• The CRT is dim.

• The SMPS transformer screeches.

• A drop of Windex on the front panel and the 1-2-5 numbers on the vertical controls come sliding off.

• There's often a burned PC board area under the cluster of 47 ohm resistors. Guess they speced the resistors too small at 1/2 watt.

• The knobs feel loose and wiggly.

"Ancient_Hacker" wrote in news: snipped-for-privacy@m73g2000cwd.googlegroups.com:

Basically the same tube as a 465. Maybe whoever cal'd it didn't get the grid bias set right.

Perhaps a bad xfmr? In my experience,few 2235's had that problem;I can't recall any. Now the early 2213/2215's had that problem.

I've encountered that too.

Probably after TEK outsourced their plastic parts production. Somebody then got a "bright idea" to save money. These days,I'd use some PC graphics program to print a clear decal to replace the lettering.(those numbers would probably also run off with Windex.)

Vert output amp? If that's it,they changed it in the A model.(redesign) I solved it by using a bit longer leads and some stand-off on the replacements.

BTW,the PCB usually was not "Burned",just the solder mask discolored.

Well,the 2200 series was meant to be low cost,not a lab scope,nor 465 quality. BUT; TEK sold a LOT of them.

Chock full of TEK-made ICs that aren't available anymore,and difficult to service.Also had a lot of HV failures. Attenuator problems,too. I hated them.

BTW,the 2335 series was meant to be a "ruggedized" field-service replacement for the 465.(that's why it's sturdier) And TEK didn't sell many,except to the US military.

Gee, I must have gotten the good one, the 2235 in question doesn't have ANY of the mentioned problems! I washed the front panel with "Mean Green" and it looks like new, with all the lettering intact.

I did find the original problem. I did not realize that the attenuator modules were in sockets! Pulling them out and cleaning up the pins solved the problem.

It looks like an OK scope, definitely in the field service category. I am truly amazed at how well the calibration has held up.

Thanks to all for your help.

Opt. 2 is AFAIR a change in the preregulator board (power supply).

..snipp..

I canibalized 7A18 that where otherwise unrepairable for these, or unrepairable 465 scopes. The x10 and x100 ceramics were useful for me, but of course it is some time effort necessary to bring parts in.

Was the method tof these times, Jim. You can find these a lot in instruments of this age. Nowadays, when you look for the 0.002 ct optimization, for a 60 to 100 MHz scope you would manufacture with PCB made in China.

hth, Andreas

"Andreas Tekman" wrote in news: snipped-for-privacy@p79g2000cwp.googlegroups.com:

I think you're wrong;IIRC,2235 had the pre-reg on the main board from the beginning. It was early 2213/15 that had the Opt.48 pre-reg PCB added,as the original triac pre-reg was noisy and failed a lot.

Well,I confess I had a "senior moment";NOW I recognize the p/n given as the common TEK hybrid attenuator modules used in 7K plug-ins and many 400 series scopes. DUH.....(smack forehead)

It's also possible that the module's pin sockets have some contamination or have lost their grip.(like my memory!) Perhaps a syringe injection of some alcohol would help here.

Thanks for the help.

...snip...

hi jim, sorry when I did not make this point clearer in the posting. You are absolutely right about the change from a triac pre-reg to the MOSFET based prereg - as a later add-on, these unit got the option-ident "opt. 48".

What I wanted to say that where even more chnages in the later 2235 scopes, that already where factory equipped with the MOSFET prereg. AFAIR the later (or very late) changes where a "opt.2". But I am sorry, I am unable to remember now if it was in the prereg, 2nd stage power supply -- all is deep in my memo is the word power supply. Apologies if my memory is wrong.

:-)) No, injection to humans only makes the liver act faster, but you loose the experience of the taste of the drink . I cannot recommend the procedure ;-)

Always great to read here in the group about Tek scopes, I enjoy all your contributions and knowledge. Thanks a lot too.

Andreas