Gallery, Projects and General > Project Logs
Oh Blimey I bought a CNC Lathe !!!!
awemawson:
OK I had a few minutes so escaped briefly to the workshop for more investigation. More close scrutiny of the board revealed an overheated track and a blown capacitor (35v 68uF) with one leg burnt off! How I didn't spot it before I don't know. Bit more tracing shows that the overheated track, although it goes very close to the blown up capacitor, isn't connected to it! In fact this track snakes around ending up on the output of a 7915 voltage regulator a few inches down the board. I decided to take my chances and, having replaced the blown capacitor (with a 35v 100uF as that's the nearest I had to hand), returned the transformer to the board, and linked the originally found blown track, connected up my ancient (probably lethal) open framed Variac, set it to half normal input voltage of 100, and powered up. No smoke, no smells, nothing got hot. Slowly wound it up to 200v and again no dramas. Gingerly started probing around (everything is floating at a high voltage). That 5v Zener diode in the hand drawn picture a few posts ago actually had 5v across it, and from my reading of the circuit that can only happen if the thing is oscillating and driving the transformer. Somewhere down the line there are two 'standard' voltages regulators, a 7815 (+15v) and a 7915 (-15v whose output track had overheated but not blown) - neither are giving outputs so something is still wrong. I need to poke around with my oscilloscope, but need first to work out what I can use as a common earth - a job for tomorrow.
Incidentally, with a 200v input, the large reservoir capacitor is charged up to 295V
Some pictures:
A/ Second burnt track and adjacent blown capacitor
B/ Capacitor removed
C/ Original blown track linked
D/ Lethal Variac - don't try this at home children :bugeye:
awemawson:
Looks increasingly as though the hybrid ic in this power supply design is the fault. It is a DK-466 and it seems that they are rare as hens teeth - only found two references to them by Googling, one was a chap looking for one, and the other is this:
http://mtc-technik.de/online-shop/mitsubishi-electric-hybrid-ic-dk-466-power-supply::7255ID.html
I've emailed them but don't hold out much hope.
The oscillator is running at about 20-30 khz which seems reasonable, and there is a power fet in series with one winding of the transformer (lets assume it's the primary,) fet and winding are across the 270v dc input voltage - but the fet is only turned on for a very short time, so it's not generating much power. Looks as though it is supposed to generate 5v at a significant current, and +/- 15v at somewhat less . Belling out the circuit round the fet and the unknown guts of the DK-466 is very confusing as it's a three layer board some of which is covered in heavy conformal coating but I think that one winding is generating a reference voltage with a zener diode, and another winding feeds the DK-466 as feedback - it's this I assume isn't working so the 'on' time of the fet isn't being tweaked.
techonehundred:
This may (or may not) not be help, but I found this link also.
http://www.antechenterprise.com/Stock.asp?Page=384
lordedmond:
Andrew
maybe of help
http://www.aliexpress.com/store/product/Special-promotions-DK-466-module-In-Stock-welcome-to-buy/217335_810050418.html
Stuart
awemawson:
Wow chaps thanks you've cheered me up no end :beer: :beer: :beer: :beer: :beer: :beer: :beer:
I suspect I'm going to have to pull the transformer AGAIN and also the DK-466 as everything round there is such low resistance that it make tracing the circuit neigh on impossible. I'm glad I got that SOIC unsoldering kit - not used it for SOIC's yet but it makes removing things like the transformer relatively easy with the very low melting point solder. I assume it's bismuth based like woods metal.
Hope to have another session going cross eyed circuit tracing after super ...
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