I'm trying to get a Tek 2445 oscilloscope working again. I replaced all of the power supply capacitors, which corrected most of the display issues. Now I'm stuck.
The trace thickens when switching volts/div, can be corrected by turning on 20mhz limit.
Adjusting sweep does not function correctly.
I've posted a video on YouTube for example of both.
http://youtu.be/92j6xMncdlo
Thank you in advance for any help.
The trace thickens when switching volts/div, can be corrected by turning on 20mhz limit.
Adjusting sweep does not function correctly.
I've posted a video on YouTube for example of both.
http://youtu.be/92j6xMncdlo
Thank you in advance for any help.
The 2465 is the "ne plus ultra" of the analog bench scope built by Tek, this guy is expensive, but a pro in this realm:
oscilloscopes@aol.com
oscilloscopes@aol.com
I appreciate the contact. I'm trying to take care of this on my own, just looking for a little advice. This was a working scope when my friend put it away 20yrs ago. Hoping someone has experienced the same symptoms.
Check all your board grounds. Looks like your front end is oscillating. Also your probe needs compensating, that's confusing the issue. Next I'd remove and clean all contacts on your hybrids. Use trichlor cleaner or Everclear. Use another scope and work back to where high frequency oscillations start. From video, should be before BW limiting.
Doc
Doc
I removed a few of the hybrids last night and cleaned them. Also removed and cleaned the contacts on the attenuator modules. I thought about cleaning contacts in the selector switches themselves, but it looks like I'll need to desolder and disassemble to do that.
The oscillation, is it possible that I'm still having power supply issues after replacing all of the caps? I checked all voltages on J119 test pins, all were in spec.
The oscillation, is it possible that I'm still having power supply issues after replacing all of the caps? I checked all voltages on J119 test pins, all were in spec.
that was my 1st impression from your vid.
were all parts replaced with same values and otherwise identical in fitment, form, and function? It's usually a bad idea to do global parts exchange unless its a simple design. trouble shoot the original problem not shoot a shotgun full-o-parts. now you may have a different issue that's harder to locate.
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i've gotten repair hints from these links for my 2465:
1. http://www.condoraudio.com/wp-conte...nix-2465B-Oscilloscope-Restoration-Repair.pdf
2. Tektronix 2465B oscilloscope teardown - Page 1
Good luck,
mlloyd1
1. http://www.condoraudio.com/wp-conte...nix-2465B-Oscilloscope-Restoration-Repair.pdf
2. Tektronix 2465B oscilloscope teardown - Page 1
Good luck,
mlloyd1
Check that power supplies are clean feeding U100, U200, U400 & ,U600. Looking at schematic, BW limit doesn't come into play before U600, the vertical output amp, which unfortunately leaves entire front end. Try isolating more. Does problem exist on Ch3 or 4? If so likely around U400 is your problem. If not does it exist on ch2 as well as 1? Back to U400. If not, U100. On schematic you're looking at diagram 4 or 6.
Doc
Doc
Funny you mentioned Condor Audio. I've been talking back and forth with Menahem for a week about an amp I'm restoring, didn't even realize he's done a scope. I have a new BK Precision ESR meter coming in tomorrow and will put it to use on the psu. There are a couple precision film caps I haven't replaced, and also the tantalum he mentions in his article. I know the voltages are correct, but there may be a lot of noise due to these old pieces.
Ch2 looks exactly the same. Ch3 and Ch4 I haven't tested, as they don't have the same adjustment ranges. I will take a look at them tomorrow as well. I don't have access to a second scope to aid in troubleshooting this one, but I may be able to get a loaner this week.
bring in the usual suspects ( they fail by turning into low ohm resistors ) replacements need low esr types
sorry you didn't want to hear my 1st answer but it's the truth
those other linked threads look more fruitful, sorry but I aint headed down that abyss
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I'd concentrate my search around U400 channel switch and power supply feeding it. (I've repaired A LOT of Tek scopes.)
Doc
I'll get on this tomorrow, and report back. Thank you very much for all of your help.
eevblog forum has some pretty detailed info on test equipment, repairs
Tek 2445A Repair, trace drift, CH1 out of spec, long startup - Page 1
Tek 2445A Repair, trace drift, CH1 out of spec, long startup - Page 1
Im amazed at folks that attempt repairs without schematics and test gear.
The one thread measuring X and Y caps out of tolerance spec then replaced seems useless.
I suspect the tantalum and diodes shorted was his problem.
I do it on power amps and power supplies but I have a mental picture of the task at hand.
The one thread measuring X and Y caps out of tolerance spec then replaced seems useless.
I suspect the tantalum and diodes shorted was his problem.
I do it on power amps and power supplies but I have a mental picture of the task at hand.
I prefer a 2465B and a Daytron 1081, which I had on my bench at Test Lab Co. But with just a -good- manual and accurately defining a problem I usually know where to look before I ever take the covers off.
But ingenuity can go a long way in leu of proper test equipment. With an RF oscillation like this I'd construct an RF sniffer probe with a 1N60p -or 1N34- and a 0.01uF cap for my DMM. I'd also poke around with a wooden probe to see if oscillation changes.
Doc
yeah sniffer probes with detectors are neat for localizing sources of RF troubles , but I truly think he's dealing with a PS problem, he said it's common to either front ends and the video he posted. Eg he slows the time base then you can see the ripple voltage. IMO this is all baseband stuff until the mega sampling DSOs came out.
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Yes, common to both CH 1&2, BUT trace cleans up on BW limit. U600 vertical and uses same supply. It -problem- is also common to both rails.
Don't follow the "baseband" idea. The 2445 is a 150MHz scope.
Doc
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