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| Hey, wanna come over and checkout my O-scope, baby? |
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| TrentO:
To decouple my oscilloscope issues from the question concerning ground straps, I've decided to create yet-another topic. I hope I don't annoy Dave too much in my doing so... and perhaps this topic should belong in the beginner-wiener section, but here goes-- What we have here is a Tektronix 2445, 150Mhz analog O-scope. Attached is a picture of the unit, with Ch.1 and Ch.2 probes attached to the calibrator. Both channels are set to 0.2V/Div and A&B Sec/Div are locked together at 0.1us. Triggering is set to Ch.2; triggering off-of Ch.1 doesn't produce anything. The picture shows that the Ch.1 trace produces a barely noticeable square-wave pattern. Ch.2 produces one that is quite readable (today, anyway.) The scope has been warming up by a south-facing window (in the northern hemisphere) for about an hour to get Ch.1 to show anything _at all_. The scope has been on for about 10 minutes at the time the photo was taken. I was hoping that someone can help me troubleshoot this problem, and tell me "oh yeah, it's the 7th fetzer valve" and that I can simply use "some 30-weight ball bearings and a quart of Quaker-State" to fix the problem. Or do I simply have the wrong settings applied? But seriously-- would it be plausible that I can fix this problem by simply replacing a cap, resistor, or by washing with copious amounts of WD-40? As an FYI-- swapping the probes back-and-forth between Ch.1 and Ch.2 has no effect. Unfortunately I don't have another O-scope at my disposal for testing, but the problem seems binary enough, not to require one. If the attachment doesn't make it, I'll email it to anyone who wants to look at it. I haven't taken the cover screws off, yet, but I can, and try to take additional photos of things people would want to see. Any help would be appreciated! -Trent "deathly afraid of the B+ voltage" O. |
| TrentO:
Hopefully Dave doesn't ban me as a spammer. Just let me know and I'll stop with the questions. Perhaps Dave could do a EEVBlog episode on how to use oscilloscopes? And the differences between analog and digital scopes. And why it might be a bad idea to try and measure the trace of a bolt of lightning. But-- what if I have simply use a REALLY-BIG grounding strap in my lightning tests? |
| Simon:
I think a vblog on using scopes would be good, while I'm fairly confident with them I'm sure theres always something to learn |
| Andrew:
The Tek 2445 is a nice scope. There were many (doggy) ones on the market (eBay) for some time, because AFAIC it was common equipment in the US Army and they retired a lot of them at some point in time. Apparently including every broken unit they had still in some storage. Get the service manual from http://bama.edebris.com/manuals/tek/2445/ and follow the repair procedures. Be careful, there are some deadly voltages inside. The service manual points out the dangerous areas and safety procedures, and they mean it! IIRC there are some parts in a 2445 that like to break but are unfortunately almost impossible to get. The hybrids are, for example, Tektronix custom parts, not manufactured since ages. (Tek sold their hybrid manufacturing to Maxim, and Maxim retired them decade(s) ago). If one of these parts is broken your best bet is to buy yet another (broken) 2445 and use that for spares. However, you'll find that you could get a new DSO for a similar price. |
| TrentO:
Thank you to Andrew and GeekGirl for providing links to the manuals. After letting the scope sit there for a few days, just to make sure its not holding on to some massive charge, I took the cover off. After careful inspection, I really couldn't find any obvious issues-- I was hoping to find a charred resistor, exploded cap or something... but everything was really clean and appeared to be in order. Based on my amateur troubleshooting, I believed the problems were limited to the analog-input sections on Ch.1 & 2; unfortunately they were contained in some pretty heavy-duty cast-aluminum heatsink / shielding 'pods' and didn't look accessible without some desoldering work. I think Andrew was speaking from experience when he said that parting-out another scope might be the only way to repair these vintage units-- peeking through a little window on these pods, I couldn't see a single discrete component inside-- it looked like a massive 'silicon chip,' with circuits that appeared to be masked on to some kind of ceramic substrate. Poking around, I also noticed that all of the boards have "Tektronix, (c) 1980 or 1981 on them-- this sucker was designed when I was in 3rd grade-- who knew? It looked newer than that. Andrew's link to the "Boat Anchor Manual Guide"-- really helped to set some perspective... and that perspective is-- Its not worth it. I just ordered a Rigol 1052E from the HappySeeds dudes on eBay. And no, I didn't buy it to further troubleshoot my Tektronix. -Trent |
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