EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: WZOLL on February 07, 2016, 11:09:45 pm
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I recently picked up a vintage Eico 460 oscilloscope at a recycling center for free. All the tubes and parts were there so i decided to plug it in. The red ON light lit up and a few seconds later a strange burning smell came from inside :-BROKE. After unplugging the scope and removing the case I noticed the transformer was very hot. I suspect the oil foil capacitors went bad and shorted the transformer. After removing the transformer i measured the windings for shorts and the resistances of the windings.
The primary winding with black wires measured 5 ohms
The secondary winding with green wires for the CRT measured .7 ohms
A secondary winding with yellow wires measured .4 ohms
A secondary winding with red wires measured 28.8 ohms
There are extra green, yellow, orange, and red with a yellow stripe wires.
None of the coils seem to be shorted through the paper.
If anyone has an extra transformer for sale if I need it or if anyone has any info at all on how to fix the scope it would be greatly appreciated :)
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Hi;
When I fire up an old tube item I remove the HV rectifier tube.
Then measure the secondary HV voltage from the transformer (400 - 600V).
The transformer has continuity - so it might still be good.
Did you check for shorts to the frame?
Put it back in, remove the rectifier and measure the red windings..
The main electrolytic is most likely dead, along with every wax paper capacitor.
Here is a link to transformer color codes:
http://www.mattmccool.com/radio/tech/pwr_trans.shtml (http://www.mattmccool.com/radio/tech/pwr_trans.shtml)
Mick M
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P.S.
This may have been sold as a kit.
Here is the manual:
http://bama.edebris.com/manuals/eico/460 (http://bama.edebris.com/manuals/eico/460)
It is not worth very much, classic TEK/HP/RCA/B&K are worth restoring, EICO/Heathkit - not so much.
It has 4.5MHz bandwidth
Remove both V8 (1V2) and V9 (6AX5) to test.
Mick M
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Always a bad idea to just plug in an old vintage bit of gear with out checking it out first. Or at least using a current limiting device. Hard to find transformers. Why I made YouTube video #21 on powering up old equipment.
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I have indeed learned my lesson about inspecting old gear before plugging it in. Don't turn it on! Take it Apaaarrt!
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i would start by recapping all the electrolytics and and (any) wax caps. Then measure all the resistors to be withing spec.
What year? Pics?
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I have a good transformer pulled from one of these scopes that I scrapped. If you need it, let me know.
DEFINITELY replace the HV filter caps, and check the electrolytics for leakage shorts before powering it up again.
The transformer has a high voltage winding for the CRT supply that is prone to shorting internally. If the transformer still gets hot with the 2 rectifier tubes pulled out, it is shorted.