Tektronics 2465 Ocscilloscope Repair

[quantumtangles]

A parts or repair Tektronix 2465 Oscilloscope (Ebay...collection only...$50 dollars) passed the Earth Bond and insulation tests for Class I devices. I plugged it in before inspecting it internally (my first mistake).

After the smoke cleared, I pulled out the power board (photo 1) and saw two failed Rifa X2 Suppression Caps (photo 2 - RIFA madness) identifiable only from their dental records (photo 3).

After replacing the failed X2 caps and two bulging electrolytic caps which failed in-circuit and out of circuit ESR tests, (photo 4 - the X2 replacements being the two light grey X2 caps), I reassembled the power board before spotting two more failed RIFA caps (an X2 and a 6800pF Y - which I also replaced (photo 5) but which I replaced (redneck style) from above, as did not want to have to take the power board apart again (ie ripped them off with pliers and soldered them in from above - nasty I know).

After putting the scope back together, it appeared to work nominally (photo 6), What you are seeing here is a signal from another oscilloscope with a built-in signal generator feeding a sine wave to the Tektronix 2465 under repair. However, the Tektronix scope is unable to process square waves (or other wave forms with high rise time).

Is this failure a result of redneck repair techniques (such as failing to replace all electrolytic capacitors)....or might it be a failed transistor or IC? It would be great to hear from people with more experience of repairing Tektronix or other oscilloscopes before I take it apart again and try to hunt down the square wave/rise time/frequency issue.

[EDIT: After posting, I saw from photo 4 that one of the resistors looks toasty and may have gone over-value....alternatively the resistor looks toasty because it was right beside the failed RIFA X2 and discolouration came from the failed X2? What do you think?]

 

[73's de Edd]

Sir quantumtangles . . . . . ( My mean machines SPELL CHECK . . . . .wants to do a serious number on your user name . . . . . hee hee hee . . .)


After posting, I saw from photo 4 that one of the resistors looks toasty and may have gone over-value....alternatively the resistor looks toasty because it was right beside the failed RIFA X2 and discolouration came from the failed X2? What do you think?
Viz . . . .
"collateral (smoke) discolouration came from the failed X2". . . . my anal orifice . . . . just look at the supplied schematic snippet and you can plainly see that both X2 caps are in series with resistors . . . one of which is being your center fried one . . . . so they would have received the full brunt of the AC line voltage across them for the time that the unit was powered up and was having foil arc over across its associated . . . . . piecemeal . . . . . X2 cap.

As far as any " try(ing) to hunt down the square wave/rise time/frequency issue. "
I'm betting that will be an interconnecting patch cable situation . . . .as you now are showing it being hooked up.
Make your HF RF waveform evaluations THRU a TEK probe or use REAL 50 ohm coax patch cable interconnects.
I would bet that cable run between the BNC's that you are using, is being akin to the using of common BELDEN 9778 shielded microphone cable .

Presently . . . . just take a TEK 10x probe of the adequate hi freq / capability . . . . end rating and connect to your calibrate SQ wave output on the right bottom corner and I'll bet that it will adjust over / and / under compensation up to a final proper square wave display / response..

SCHEMATIC SNIPPET . . . . .






Pee Ess . . . . . . What low ball price are you going to give the good wyfe for being this units monetary evaluation ?

Although I have two 465's, a 466 Storage with DMM, a 454 and a mini 305 with DMM and battery pack . . . . .your 2465 is developing a drool coming out of mine lips m m m m m m m m m m m 300 megallinghurts . . . .


73's de Edd . . . . .

Sometimes . . . . . Auto correct / Spell Check really passes me off ! ! !