EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: DaJMasta on December 26, 2020, 06:31:23 am
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I recently got my hands on a Keithley 6517 electrometer that wouldn't turn on. Replaced a burned out fuse, burned out a second in about 10s but saw the front panel light up. With a 2A fuse instead, the instrument appears to boot fine, but the transformer lights up like a candle on thermal (nothing else on the board does), it draws 1.5A from the wall (normally a 1/2A fuse), and this behavior continues even with ALL of the secondary sides disconnected and when it's clearly not booting but the power switch connects the input windings of the transformer.
So my primary side is partly shorted, but in a way that it will actually still boot (haven't let it fully self check, there may be output winding issues as a result), but at least in some respect it will function, and I'm wondering what my options look like. The transformer is a Multicomp DV-155-A or 129-3075-00 TR 297 Rev A (whatever the naming system is), and it seems like quite a project of a rewind if I were to take that route as it has no less than 4 connectors worth of output windings - 29 output connections and 6 input connections - so it sort of seems like a nightmare of a project for someone who hasn't rewound a transformer before.
Is this part available from Keithley/Tek? Would they even bother selling a part? Any info on whether it appears in other units (I would assume not, given the output configuration) that I could get for a replacement part? Is it worth trying to contact multicomp for a spare? Should I just bite the bullet and get to rewinding it?
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Can you run it on a Variac? I'd be interested to see if it works normally at 60 VAC or so. Also, is this a setup where there is a voltage selector that lets you select 100/120/220/240 volts instead of just 120/240?
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There is a single 115V/230V selector switch on the back, but inside, under the input filter, there is a second switch that isn't described on the silkscreen. Switching it does appear to change where input voltage is present on the input connector, the transformer is currently pulled so I haven't tested it powered up.
The source was in the US, it was set to 115V on the switch, and the 1/2A fuse is as specified for this voltage level (only 250mA at the higher voltage setting), so I wouldn't expect it to be a configuration problem.
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The transformer PN is TR-297A. You can try by asking here (https://info.tek.com/www-request-parts-information.html?_gl=1*u9byfo*_ga*ODYwNjc3OTA5LjE2MDg5NzQyNzA.*_ga_1HMYS1JH9M*MTYwODk3NDI3MC4xLjAuMTYwODk3NDI3Ny4w&_ga=2.91367390.576173302.1608974271-860677909.1608974270).
You will thus be able to evaluate, based on the asking price, whether it is more convenient to obtain the original spare part or rewind the transformer.
I have managed to get both electronic and cosmetics Tektronix/Keithley spare parts here in Europe, I think in the US it is even easier.
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The source was in the US, it was set to 115V on the switch, and the 1/2A fuse is as specified for this voltage level (only 250mA at the higher voltage setting), so I wouldn't expect it to be a configuration problem.
I wasn't suggesting that it was a configuration problem, but rather exploring the possibility that there might be enough primary windings remaining to rig up a configuration that works. Using 60VAC would test whether that winding was shorted in half. You mentioned 6 primary leads so there must be some additional level of complexity.
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Seems like Keithley used some garbage wire to make their transformers, I think
Have a K182 with toasted transformer here as well, I partially unwrapped it and the wire coating is crumbling away.
Also heard lots of other stories from people with Keithley gear and bad transformers.
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The transformer PN is TR-297A. You can try by asking here (https://info.tek.com/www-request-parts-information.html?_gl=1*u9byfo*_ga*ODYwNjc3OTA5LjE2MDg5NzQyNzA.*_ga_1HMYS1JH9M*MTYwODk3NDI3MC4xLjAuMTYwODk3NDI3Ny4w&_ga=2.91367390.576173302.1608974271-860677909.1608974270).
You will thus be able to evaluate, based on the asking price, whether it is more convenient to obtain the original spare part or rewind the transformer.
I have managed to get both electronic and cosmetics Tektronix/Keithley spare parts here in Europe, I think in the US it is even easier.
Thanks for the tip, I've dropped them a line.
Took a picture of the transformer in question to see the bird's nest of a set of secondary taps. From measuring it a bit, the primary side actually seems alright - two windings with a center tap that's very off center on each - but in measuring the secondaries I'm seeing most of the connections on one output group at various resistances that seem very wrong for this gauge of wire and for relatively low voltage operation - 2, 21, 38, 42, 986, 1k.... some of those definitely don't seem right and shouldn't connect to 5 other output lines.
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No reply on the first attempt so I contacted them again and just heard back.... they want $786 for a replacement transformer :palm:
Surprisingly, the reply said the part number was TR-297D, maybe there were more revisions for this very reason...
So I guess I'm rewinding it myself. Any tips for a solvent that can separate the laminations? I figure if I can get that out, actually counting the windings and format of the wires around the form should be simple, if not tedious, work, then I'll just need appropriate wire for winding the replacement.