O-scope woes

I though yesterday was going good-finished some work early, found some test equipment on craigslist and had it in my hand 30 min later (Fluke counter/timer). Of course, talked to the old timer for awhile about scopes, and I told him I was in the market for a digital scope should he come across one. He commented that he just trashed several analog scopes because the trace disappeared and it was too difficult to get inside of them (off brand).

Quite ironically, I got home and hooked my freq synthesizer to the counter to see if everything matched. With the synthesizer set to 10Mhz, the counter showed 9.992Mhz. Not real bad, but I wanted to see what the scope showed as well. I had it powered up and had a hard time getting a good trigger on it. Finally, it locked on. Disconnected the probe, and that's the last I saw of a trace on any channel. If I quickly rotate the trigger level knob, the trace flashes for ch-A, ch-B, and ch A+B (as set). It's a Tektronix 2246. I'm somewhat attached to this model, even though I know I need a digital unit (just didn't figure it would be NOW)

I have the service manual in pdf, and perhaps I can get to opening it up this weekend. Has anyone run into similar problems?

Not on a Arduino. Probably the wrong forum for scope questions.

Paul

Paul_KD7HB: Not on a Arduino. Probably the wrong forum for scope questions.

Paul

Well, it is electronics, and it is used to check arduino circuits.....

tinman13kup: I have the service manual in pdf, and perhaps I can get to opening it up this weekend. Has anyone run into similar problems?

If it has a lot of use sometimes a worn pot can be the culprit.

I have the tek 2225 (50 MHz), still going strong after 30 years with intermittent use. Focus knob is a bit dodgy though and needs to be tickled.

EDIT

Thinking about it, the trigger pot and the focus pot often get very small adjustments IME.

Maybe it has a small worn bit on it somewhwere.

I have a Tek 2205 and 2211 myself. Everyone seem to think you need the latest and greatest high speed scope but these just work fine. I picked them up for $40 and $50.

Old equipment can indeed be a bargain, but typically weighs tons and requires loads of space (and strengthened shelving!). Modern units are less cumbersome and do more (= have loads of confusing options!).

As for 'scope settings, a device with "factory preset" button is great for backing out of some obscure mode you don't understand or apparent catatonia. In a shared lab you'll always find someone's left a scope in a bizarre set-up that takes minutes to figure out!

MarkT: As for 'scope settings, a device with "factory preset" button is great for backing out of some obscure mode you don't understand or apparent catatonia. In a shared lab you'll always find someone's left a scope in a bizarre set-up that takes minutes to figure out!

Oh yes. We had an early model Waveform analyser demonstrator which came with a similar sized panel of preset buttons. Made fast testing a doddle , until someone worked out how to reprogram the buttons. >:(

Really old stuff can be heavy but i have had many working bargains which were not too bad. Only caveat as i mentioned earlier is the POTs can be duff and replacement is not always posssible.

Yes, old equipment is cheap and plentiful, and I understand there are generally reasons they are that way. Still, it’s hard to justify a $10k piece of test gear for a hobby. My HP freq synth is big, and weighs upwards of 75lbs, only outputs to 13Mhz, but it only cost me $150 for it AND 2 logic analyzers.
I have been thinking about a Rigol digital, but I think it’s only a 20Mhz model. I’d like a Ghz unit, but they are pricey. This Tek is 100Mhz if I can bring it back to life.

Yeah, my focus is a bit dodgy as well. One bump and it gives you a headache trying to see the signal. Guess I’ll start with the pots in general and go from there.

tinman13kup: . I'd like a Ghz unit, but they are pricey.

Rented a 2GHz unit recently. Probes cost more than the unit.

Boardburner2: Rented a 2GHz unit recently. Probes cost more than the unit.

...which cost more than all the different test equipment I have.

Still, somehow the engineers were able to make do with this old stuff.

tinman13kup: Still, somehow the engineers were able to make do with this old stuff.

This is because they / we weren't doing suff as complex / fast as we do today.

sounds like simple contact cleaner fix try using an old Heathkit Vacuum tube scope without dc coupling just a curve tracer now but it still works

I had one of those. Either the focus or intensity pot failed i forget which. Could not fix it as it was the tapped pot which i could not replace. The carbon track wore out.

Just to close this out, I opened the case, did an inspection-only finding small amounts of dust accumulation, then turned it on. I ran each selector knob/button through their respective ranges and placed them back to get a viewable trace, and it looks like the culprit was the Trigger Mode. I ran it down to SGL SEQ, and then back up. As soon as it hit NORM, I had all the traces back.

Since I had it opened and had the service manual up, I decided to go through the calibration list, doing what I could with what I have. -All the voltage levels were within specs, some getting close to the limits, but I didn't adjust any -All the horizontal tests I could do actually fell within their specs, so nothing was adjusted -Some vertical adjustments were done, only because it is set from a baseline-so it may have been good to start with

In fact, the only issues I found are the calibrator, which seems to be putting out 1.127Khz instead of 1Khz, and the DC voltmeter.

Using a 5V precision voltage source, the display only reads 4.74V. I want to investigate this a bit further.

As for the calibrator, I don't believe it's adjustable. Using the time cursors, the scope reading says 1.127Khz, connecting the calibrator to a Counter also indicates 1.127Khz. Inputting a 1Khz signal into CH 1/2 from a freq synthesizer, the Time cursors and counter both indicate 1Khz.

All equipment was allowed to warm up 15min.

I think my counter is bad though. With no leads hooked up, all it displays is 60.....

An old oscilloscope is not a precision instrument

I use it to see if there is a signal at all and what it looks like.

If you need more precision, use a multimeter and a frequency counter (mine is self-built with Arduino).

arduinoaleman: An old oscilloscope is not a precision instrument

I use it to see if there is a signal at all and what it looks like.

If you need more precision, use a multimeter and a frequency counter (mine is self-built with Arduino).

I hope you are being sarcastic.... I'm not talking an old heathkit here. The correct response would be "look for a new DSO" not an arduino freq counter. I've accumulated many DVOM units, and each and every one of them has their own idea what 5v is. Only 1 of the units has a calibration sticker on it, and it is the only one to read 5v as 5v. It also wasn't cheap.

tinman13kup: I think my counter is bad though. With no leads hooked up, all it displays is 60.....

That's mains pick-up, I wouldn't worry (unless your mains is 50Hz!!)