Moderators: Dave Moll, Andrew Davie, Steve Anderson
Steve Anderson wrote:Proceed one stage at a time...unplug the transformer secondaries - so they are not feeding the power supply rectifiers etc.. If it doesn't blow the fuse check anyway the output of each winding - they'll be higher than usual due to having no load.
If that's OK, plug the transformer output into the power supply board and disconnect all outputs from it - measure the DC output voltages...again they may be a bit high due to no load - if no fuse blow leave it on several minutes, recheck.
If still OK, the next suspect is the EHT generator. There's a link shown between the +12V supply and the EHT generator (W801/P801), remove it. One-by-one plug everything else in. If that's the last thing unpowered it's probably the culprit. Ah! It appears W801/P801 are part of a multipole connector, so that suggestion might be not so easy...
Steve A.
Harry Dalek wrote: ...came out of the blue never had a problem with it till now .
Steve Anderson wrote:Harry Dalek wrote: ...came out of the blue never had a problem with it till now .
In most cases the power supply is the highly stressed part of any device, in this rather special case it's probably the EHT inverter. But take it step by step and you'll find the culprit in time. Finding replacements or substitutes in critical parts is always harder than the diagnosis.
I hope it isn't the EHT supply, the low voltage power supply would be easy to find spares...
Steve A.
Steve Anderson wrote:It's wonderful when fixes are as easy as that! Unplugging and plugging in again on all internal connectors is assumed before anything else is done. Take the cover(s) off, unplug, re-plug, try again. If it works treat yourself to a beer!
Most failures are related to electo-mechanical components, switches, connectors, pots, relays, anything with moving parts...especially if the unit is quite old and/or stored in a dusty/damp atmosphere...but that's not the case here it seems.
Fuses often 'tire' with age, replace them before even reaching for a screwdriver...those that are externally accessible anyway. but look for any internal ones and replace. You may as well do it anyway while you've got the cover(s) off.
Steve A.
Steve Anderson wrote:OK, good news, you're back in business...
Steve A.
Steve Anderson wrote:What a headache! Very unusual for a transformer to fail on its own, usually the result of an overload or damp storage, but if it's smelling of the usual burning transformer smell, it's toast - whatever caused it.
The 'wobbly' line ramp - check the pin numbers are correct between the 4040 and the DAC-08.
The slower ramp looks wrong too, it should be a perfectly straight sloping line - did you have the 'scope on AC coupled input? It needs to be DC coupled at these low frequencies...where in the circuit did you measure these waveforms?
Steve A.
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