Re: Tektronix TDS1002 w/ Ault SW424RA0000F03
Indeed! Even after having encountered it on low voltage barrel connectors many times before it just didn't occur to me.
Just maybe the time constant of 30kΩ and 82uF and D5's zener voltage works out to something?? But that doesn't seem likely.
8 hours of running the power supply on its own (logging the 3.3V and 6V rails with a logic analyzer), and 12 hours of powering the 'scope later ... it seems to be just fine. Success!
Anyway, I'd like to thank all of you for walking me through...
rnjacobs
Member
Last Activity: 12-08-2016, 12:23 AM
Joined: 12-02-2016
Location: Seattle, WA
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Re: Tektronix TDS1002 w/ Ault SW424RA0000F03
Ok.
Swapped out IEC cable for one that felt "tighter". (Actually did this yesterday)
Reflowed solder on C14 socket, switch, fuse, and thermistor(??—green thing silkscreened TH)
The solder on the C14 socket looked good before hand, but the socket was kinda floppy, and it's definitely tighter now.
Tested, had one more power failure. Removed power supply from mounting posts so that I could get a voltmeter onto the solder side and ... haven't been able to reproduce since.
...Leave a comment:
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Re: Tektronix TDS1002 w/ Ault SW424RA0000F03
Only have 3DMMs, but:
3.3V line: 3.353, decays rapidly on failure
-4V line: -3.81V, falls to 1V on failure and then decays slowly
(from memory, not retested) 35V line: 31V, decays very slowly on failure
main input filter cap: 161.2V, falls almost instantly to 25V on failure, then slowly falls if supply stays in failure state
Secondaries all come up about 2 seconds after the main input goes back to 160V.
This tentatively looks like the same behavior if I just use the power switch...Leave a comment:
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Re: Tektronix TDS1002 w/ Ault SW424RA0000F03
Less convenient thing: Removing L5 (the ferrite choke that connects the CCFL inverter to its -4V supply) doesn't fix anything.
More convenient thing: I can make the arcing sound (and power supply shut down) appear by just rotating the power supply in space. (While mounted to the oscilloscope: I'm doing my best to avoid any flexing) However, I still can't get to happen in a reliable enough manner to e.g. localize the sound using a microphone.
Any suggestions for other ways to find it?Leave a comment:
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Re: Tektronix TDS1002 w/ Ault SW424RA0000F03
Glows the standard CCFL white (i.e. not old CCFL pink). Visual inspection of the wire shows no visible defects. Inspection under the right-angle protectors at the ends of the tube show an intact wire. Continuity test shows nothing funny from each end of the tube to the connector.
There's no visible damage on any component anywhere. No bulging capacitors, no leaking electrolyte, no burned wires, no visible heat damage on the FR4 or hot melt, no broken epoxy packages.
Nope, seems stable. The 'scope's service...Last edited by rnjacobs; 12-04-2016, 03:49 PM.Leave a comment:
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Re: Tektronix TDS1002 w/ Ault SW424RA0000F03
Total use on the 'scope is really quite low, maybe a thousand hours total, and with none of the standard CCFL aging behaviors. But the only test equipment I have, other than this 'scope itself, is a logic analyzer and three voltmeters (that are only rated up to 600V)
C28 and C29 are filter caps for the 35V LCD contrast supply.
PC1 is supplied from a pair of traces the winds all the way up the left (and low voltage) side of the board: IC2, R32, R29, R28.
Well, ok, more exact description of symptoms:...Leave a comment:
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Tektronix TDS1002 w/ Ault SW424RA0000F03
What: Oscilloscope (Tektronix TDS1002) power supply made by Ault
Symptom: Power supply randomly browns out and reboot. Temporarily fixed for a year or two by unplugging the CCFL from the power supply. (Turned it on again today and now it's browning out even so)
Power supply: Ault branded switching power supply that emits (according to the silkscreen) -4V, 3.3V, 5V, and a floating 35V (for LCD contrast).
All but one capacitor labeled "Lelon" ... which I see is in the "bad manufacturers" list. None obviously damaged, but I lack a capacitance... -
Re: New Members - please post your introductions here
Hello, everyone!
I'm a firmware engineer, and not versed in power supply design at all, and my oscilloscope started going into a reboot loop that is prevented by removing the backlight. That seems to me like the power supply is the source of the problem... so hopefully I'll be able to find guidance here.Leave a comment:
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