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Thread: Daiwa SS-330W Switchmode Power Supply fault

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    Default Daiwa SS-330W Switchmode Power Supply fault

    Hi All, is there any switch mode power supply gurus in here? I was given a non working Daiwa SS-330W Switchmode Power Supply to have a look at and I have narrowed down the fault to one of the transformers (T3 according to the schematic). Any ideas on where I might find a replacement? I have tried all the usual places, Element14, RS and such but haven't had any luck. I have also tried the manufacturer but they haven't replied yet.






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    What makes you certain that it is faulty ?
    Transformers are the least likely to fail in these supplies.

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    I wouldnt mind betting that it has a built in thermal fuse which has gone o/c , normally on the input side check for ohms ? maybe carefully strip insulation on outside and find the fuse , its normally viewable as it has a tinned lead where the windings are copper coloured

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    Quote Originally Posted by Reschs View Post
    What makes you certain that it is faulty ?
    Transformers are the least likely to fail in these supplies.
    There was a blackened area on the board under the transformer, one of the tracks connected to it showed signs of over current. I removed the transformer from the board and checked the winding resistance and found both the secondaries are open circuit. And it seemed like a good place to start.

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    Quote Originally Posted by hinekadon View Post
    I wouldnt mind betting that it has a built in thermal fuse which has gone o/c , normally on the input side check for ohms ? maybe carefully strip insulation on outside and find the fuse , its normally viewable as it has a tinned lead where the windings are copper coloured
    Yeah, something has definitely gone splat. The fault was reported to me as the main fuse pops when switched on.

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    Is the secondarys the four pins ?

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    main fuse popping is going to be the mosfet shorted . With the tranny out power it up and you should have about 325 v dc on the filter caps if not the input bridge rectifier is fvked tell me more ?

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    whoa back there that tranny is not capable of 30 amps so its a control supply tranny , not the main supply tranny

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    Quote Originally Posted by hinekadon View Post
    main fuse popping is going to be the mosfet shorted . With the tranny out power it up and you should have about 325 v dc on the filter caps if not the input bridge rectifier is fvked tell me more ?
    I am back on site for a week so I will have to have a look when I get home. I'm always very cautious these days powering up switchmode power supplies when they are exposed. The worst boots Ive ever had has been from switchmodes. DC Hurts.

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    yep a check on the circuit dia says that t3 tranny is to supply the control volts/ amps of the four transistors base for the choppers you may end up thinking its not worth repair given its age , the chopper transistors are the type used in the hoz stage of old crt colour tvs and they are specialized matched pairs they may be hard to find as well, q6 q7 q11 q12 are most likely stuffed as well as they are the drivers for the choppers good luck Cheers Don

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    Quote Originally Posted by hinekadon View Post
    whoa back there that tranny is not capable of 30 amps so its a control supply tranny , not the main supply tranny
    Yeah definitely not a main supply tranny.

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    Might be a custom wound part ; discontinued model, so not sure how you'll go with manufacturer.

    Bit odd (although not unheard of) for those to fail, considering where it is in circuit, without something else being awry....ie; output drivers (A950. C2120) connected to the upc494 PWM chip (which is a pet hate part of mine), else the main switching transistors (C2625) being bad (or having blown in the past & replaced)....any evidence of any previous repair/rework attempts? I take it that (with the driver transformer removed), you've 'scoped the transformer input waveform coming from Q6,7,11,12?

    Anyhow, 30 odd years ago we used to do small transformer rewinds, but these days I suppose it depends on how 'married' you are to the unit itself --- if you get stuck and it's a 'until death do we part' affair, you may end up with a rewind being the only way out...ie; un-tape and separate the ferrite core halves, and the carefully unwrap the bobbin windings paying particular attention to number of turns of insulation & wire windings, measure the wire gauges used for the windings, and rewind it with same wire gauge. number of turns, and insulation layers...blablabla. If the case was that the faulty transformer was a common size part (they often are), we were more 'sacrificial' than that...ie; as the rest of the hardware was being replaced with new, all you really need is the number of windings & wire gauge really, and just break the ferrite core off enough to do that (saves soaking them in solvent to soften the conformal coat enough to get them apart)... I suppose it's a bit of an archaic skill nowadays for equipment like this, but back then with well made stuff, it was worth the fiddly repair -- now ppl mostly go and by new stuff, and deem this sort of fix as BER (beyond economic repair)...charging a couple of hour's labor just to do that work, makes for a hellishly expensive transformer.

    HTH =)

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    Quote Originally Posted by wotnot View Post
    Might be a custom wound part ; discontinued model, so not sure how you'll go with manufacturer.

    Bit odd (although not unheard of) for those to fail, considering where it is in circuit, without something else being awry....ie; output drivers (A950. C2120) connected to the upc494 PWM chip (which is a pet hate part of mine), else the main switching transistors (C2625) being bad (or having blown in the past & replaced)....any evidence of any previous repair/rework attempts? I take it that (with the driver transformer removed), you've 'scoped the transformer input waveform coming from Q6,7,11,12?

    Anyhow, 30 odd years ago we used to do small transformer rewinds, but these days I suppose it depends on how 'married' you are to the unit itself --- if you get stuck and it's a 'until death do we part' affair, you may end up with a rewind being the only way out...ie; un-tape and separate the ferrite core halves, and the carefully unwrap the bobbin windings paying particular attention to number of turns of insulation & wire windings, measure the wire gauges used for the windings, and rewind it with same wire gauge. number of turns, and insulation layers...blablabla. If the case was that the faulty transformer was a common size part (they often are), we were more 'sacrificial' than that...ie; as the rest of the hardware was being replaced with new, all you really need is the number of windings & wire gauge really, and just break the ferrite core off enough to do that (saves soaking them in solvent to soften the conformal coat enough to get them apart)... I suppose it's a bit of an archaic skill nowadays for equipment like this, but back then with well made stuff, it was worth the fiddly repair -- now ppl mostly go and by new stuff, and deem this sort of fix as BER (beyond economic repair)...charging a couple of hour's labor just to do that work, makes for a hellishly expensive transformer.

    HTH =)
    Thanks very much for your reply. I now have a few more things to have a look at. No rework/repairs that I can see except for what I have done. I ran out of time when I was home last to do any in-depth testing. That's next weeks job. I'm not super married to the thing. Was given to me to have a play with, but I tend to like to examine all options before I bin things.

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    If you want a project you could change the choppers for a pair of mosfets and do away with the t3 and feed the mosfets thru single transistors to the gates the upc 494 i another pain but it could be substituted for a easier cheaper option
    sorry Im getting old you would have to use a couple of optocouplers in place of the transformer for isolation
    Last edited by hinekadon; 01-07-21 at 02:41 PM. Reason: oops

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    Quote Originally Posted by hinekadon View Post
    If you want a project you could change the choppers for a pair of mosfets and do away with the t3 and feed the mosfets thru single transistors to the gates the upc 494 i another pain but it could be substituted for a easier cheaper option
    No, you cannot do that - you lose the isolation from the HV side -- this is the primary reason they used a transformer there, to stop the HV reaching the control side should the output switchers go internal short, and the HV appears on the transistors' base.


    Quote Originally Posted by Kaelnorr View Post
    Thanks very much for your reply. I now have a few more things to have a look at. No rework/repairs that I can see except for what I have done. I ran out of time when I was home last to do any in-depth testing. That's next weeks job. I'm not super married to the thing. Was given to me to have a play with, but I tend to like to examine all options before I bin things.
    Ah-huh, you'll want to check everything around the main switchers ;



    Check resistors and diodes are still good, replace C39/C40 as matter of course (incase they were damaged), and all four transistors. I would also replace the bridge rectifier as a routine of repair here.

    Given the transformer secondaries are burnt out, you live in hope the transformer insulation held up, and the HV didn't jump the transformer --- it that happened, Q6,7,11,12 would've worn it, so you have to check them as well.

    Typically I'd also replace the upc494 as well, along with all the low value electrolytic caps thereabouts.

    You'd probably be looking at <$20 for all these components -- the transformer itself will be the hurdle, so I'd be making sure I have a replacement route for that, before I spent any money on parts.

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    Quote Originally Posted by wotnot View Post
    Check resistors and diodes are still good, replace C39/C40 as matter of course (incase they were damaged), and all four transistors. I would also replace the bridge rectifier as a routine of repair here.

    Given the transformer secondaries are burnt out, you live in hope the transformer insulation held up, and the HV didn't jump the transformer --- it that happened, Q6,7,11,12 would've worn it, so you have to check them as well.

    Typically I'd also replace the upc494 as well, along with all the low value electrolytic caps thereabouts.

    You'd probably be looking at <$20 for all these components -- the transformer itself will be the hurdle, so I'd be making sure I have a replacement route for that, before I spent any money on parts.
    That's awesome, thanks very much. I am looking forward to getting home next week to dig further into this. I did hear back from the manufacturer and apparently they don't make these or have spare parts anymore and I should speak to the local distributor who, according to their website, is Strictly Ham. But I doubt he would have parts just sitting on the shelf. I'll ask anyway, won't know if I don't ask. Failing that I guess I'll be trying my hand at tranny rewinding...... Any other forum and I'd be a little concerned about myself saying that.

    Cheers.

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    Quote Originally Posted by Kaelnorr View Post
    That's awesome, thanks very much. I am looking forward to getting home next week to dig further into this. I did hear back from the manufacturer and apparently they don't make these or have spare parts anymore and I should speak to the local distributor who, according to their website, is Strictly Ham. But I doubt he would have parts just sitting on the shelf. I'll ask anyway, won't know if I don't ask. Failing that I guess I'll be trying my hand at tranny rewinding...... Any other forum and I'd be a little concerned about myself saying that.

    Cheers.
    I'm not surprised you bummed out with the manufacturer, and I'll be somewhat astounded if the dealer has any.

    If you've time to watch some informative videos on the matter, the 'diodegonewild' youtube channel is good viewing ~ the man knows his stuff. You mentioned previously about being reticent powering up 'known bad' mains equipment, well once upon a time we used a high tech device known as an 'incandescent light bulb' in series with the mains supply, to lower the pucker factor involved =)

    Earlier this year he did a vlog on a 12v/50a SMPS power-supply repair, diagnosis, repair and discovery of a dodgy transformer, and forms a good treatise on how to autopsy and rewind these types of transformers - slightly different circuit topology, but the same principles apply. You may also find the reason for the transformer in your unit running hot, is because of the use of copper plated aluminium wire windings ... and further to that and worth noting here, he's working on the *output* transformer in the vids (this is T1 on your unit), not the driver transformer you've found bad, and one cannot discount *your* unit's output transformer might have gone bad and caused the transistor(s) to fail, so that's another thing to keep in mind -- as you can see in the vids, there's no outward visible sign that transformer had failed, it's only when you open them up do you get to find/see any damage.




    Last edited by wotnot; 02-07-21 at 11:14 PM.

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    Both good videos wotnot - I just can't handle his voice..
    How to rewind those types of transformers is interesting as is the use of copper plated aluminum wire windings.

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    Those videos are awesome. Thanks very much for that. That accent though.... Couldn't work out where its from at all.

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    From Czechia (the Czech Republic) ~ I used to work with a guy from there, so I'm kinda used to the accent =)

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