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Thread: Quantar Exploding Onan Power Supply

  1. #1
    ev351 No Longer Registered

    Default Quantar Exploding Onan Power Supply

    Hi all,

    So, a Quantar went off air today, and I went to site to investigate and found that the trusty Onan had gone fireball and ruined my day. I have been looking about on the net and found many people who are aware of the Onan Fireball, but so far no discussion on the actual fault and what actually fails when these things blow. I found it interesting that the supply had actually tripped the house circuit breaker at site instead of blowing an internal fuse or something.
    So, does anyone have any info on what actaully goes wrong with these things? Its from a High power UHF quantar....


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    I'm betting it has to do with dust (semi-conductive) shorting out caps or other components, which causes the fault.

    I'll scour the net and see if I can find something about the Onans for you.

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    From Batboard:

    Quote Originally Posted by ASTROMODAT
    Batdude, watch out if you have the old Onan switching supply on your Quantar! I was looking back through the Batboard re: Quantars, and found out the following:

    If your unit was manufactured around 1999, or maybe even a little newer than that, it might well have the ONAN P/S. Supposedly, someone on this board claimed that the Onan P/S had a design flaw involving some exposed leads/contact points carrying a 400 volt potential. If you blew off dust from the P/S and it migrated into the supply, or wiped it with a rag to where the dust fell into the supply, it could cause an arcing situation, and/or possibly blow a few caps. This was subsequently corrected with the Motorola designed/manufactured switcher.

    If your P/S is made by M, you are fine. If it's an Onan, be careful to only clean it with the A/C OFF!

    Larry

    Quote Originally Posted by xmo
    Based on the posted picture, Batdude has the exploding Onan supply. The Onan supplies have a fan in the back, the new Motorola supplies have a fan that is visible from the front.

    When these babies let go it sounds like a firearm discharge. I had one go off about two feet away. Smoke and flames shot out three - maybe four feet. I had a Motorola project manager in the room at the time and he was even closer. He reported the problem to the factory.

    In the interim, before the new Motorola supply was ready to ship, Motorola had Onan put a shield plate in these so the explosion is contained inside the supply. You can tell if you have the shield by looking right through the front. If it is there, you can't see any parts, just the plate.

    I believe the problem does originate from accumulated dust. We had several of them fail and it always was when someone was on site. I think just being there stirs up dust in the air or else vibration from bumping the rack the staion is in dislodges dust and causes the failure.

    My ham Quantar has the new supply, but if I had one of the Onans, I think I would drill out the rivets and look it over inside. Perhaps if you cleaned it regularly the problem could be averted. Maybe even install your own blast shield.

    The new supplies have been more reliable, but we even had one of them fail with a loud pop - just no smoke and flames. In any case, I have learned to NEVER stand directly in front of a Quantar!

  4. #4
    ev351 No Longer Registered

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    Thanks for that, I found this kind of info too. Its christmas day here, so maybe tommrrow i will pull ir down and have a look. I would like to repair it myself rather than letting someone else at it. After all it is just a power supply. There is much disscussion about how these units always fail, and im sure even if you have limited exposure to the quantar they will be well aware of this fault. Unfortunately everyone just seems to take them in for repair.

    Incidently mine failed in the dead of night, it was not being cleaned or disturbed, I will be interested to see how much dust it has in it.


    Ev.

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    The reason no one tries much to repair the Onan supplies is there is no published service documentation for them. The BIG Quantar manual has schematics for the later Motorola-designed supplies, but like most OEM factory supplied stuff only the OEM contractor has any sort of information about them, and they ain't telling...

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    I've never experienced an Onan failure (yet) so would appreciate details on the parts that have died. Better yet post a picture of the damage. While the dust theory is pretty strong I'd like to offer another, these supplies don't seem to fail when run from 230 VAC so it could be either the simple fact that the current drawn is half on the higher voltage or a more subtle fault to do with the 115/230 VAC auto switching. And that this is fatal only on 115 VAC.

    I've not seen the Onan schematic but generally dual voltage switching supplies full wave rectify 230 VAC and charge a pair of supply caps wired in series or voltage double 115 VAC by alternatively charging each of the pair caps. Either way gives 300 VDC raw to feed the actual DC to DC converter circuity. My theory is that something goes wrong with the change over switching between the two input configurations, maybe triggered by dust or maybe an overvolt/brownout transient. Pure speculation.

    Merry Christmas
    Last edited by Astro Spectra; Dec 25, 2012 at 02:24 AM.

  7. #7
    ev351 No Longer Registered

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    Hi all, as you can see I have nothing better to on Christmas day So, I have pulled the supply apart. This is a strange task to begin with. You have to drill two rivets out on the rear of the case and then remove one screw near the on/of switch. The funny thing is, I do not think that I have the usual fault. If you look at the pics, the part that has smoked is the silver box on the bottom right of the power supply, it really smells bad and when I arrived on site and turned the breaker back on, it tripped the breaker and smoke came out... There is an input fuse soldered onto the PS board, it is not blown, so I think that the fault lies in the silver box. I have also attached a picture of the circuit diagram for that box as there is a sticker on the box with the diagram. If there is someone smart enough, i would love and explanation of that circuit.

    Also, that box is permanantly soldered shut, it looks like is will be fun opening it.
    The only other thing to note is that this power supply is running off 240v not 110v if that changes anything...

    Ev.2012-12-25 21.42.07.jpg2012-12-25 21.33.37.jpg

  8. #8
    ev351 No Longer Registered

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    OK, so i put that part number into google, and it appears that this is just a filter. So if im lucky maybe the supply is ok. After looking at that diagram, I think that I can connect the mains directly to the supply and bypass that unit to test if the rest of the supply is ok. If it is, then I can open that up and either replace smoked parts or replace the unit itself... Anyone think likewise???

    Ev.

  9. #9
    ev351 No Longer Registered

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    Update:
    I could see no reason that I cannot power this thing up without that filter, so i rolled the dice, and lucky me, it powered up. So i drove back to site and slipped it in. The quantar is temporarily back on air until I can arrange a replacement filter... Does anyone have any blown up AC high Onan type supplies lying about??

    Also, I guess this is a bit of rough fix, but if you are desparate and you have the Onan type supply which is exhibiting a short accross the AC input terminals, then maybe its worth opening it up and bypassing the filter, as it might just get you going in an emergency...

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    Hi ev351,

    Did you just us some 240V wire to bypass the filter? seems easy enough!

    Cheers,
    Matt

  11. #11
    ev351 No Longer Registered

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    Hi Matt,

    Yes I just cut up a IEC lead, crimped on some lugs and pushed them onto the power supplies main board. I know its rough and ready, but it proves a point and gets it going until some spare parts can be sourced.

    Ev.

  12. #12
    Will No Longer Registered

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    The filter is a and AC line filter, it may be able to open it up and fix the smokey part(s).

    Power Supply fan goes bad too, replacement for the Onan power supply.

    Here is the part number for a new power supply fan: ADDA Fans AD0912HB-A73GL-LF

    This is the 92 mm X 20mm fan with the tachometer leads.

    Onan power supply 3-70506-0000 Mot# 01-84906T04.
    The integrated circuit thermistor in the Onan power supply is a Honeywell TD5, Digi-Key Part Number 480-2017-ND
    About 2100 ohms with a 1.55 voltage across it at 90 deg. I have photos.

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    That filter is called a "Bathtub" filter, and it is an LC network made to suppress EMI from the switching regulator getting back into the AC line. It's required to pass FCC emission regulations but in practice you probably can get away without it. The only useful function it does provide is the MOV devices across the line which are most likely what shorted from a voltage spike or lightning hit. If you get the same situation without the filter, the transient will go into the supply which is a bad thing. If you have a UPS or power conditioner you can plug into that would probably help immensely.

    A quick search shows an exact replacement on EBAY for about $200.00: http://www.ebay.com/itm/JMK-INC-EF10...-/220460003572

    You might be able to use a generic filter module too something like this: http://www.lightobject.com/AC-electr...-10A-P774.aspx

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    If you do try and make a DIY repair it will most likely be the over voltage varistor aka MOV. However, if it's one of the caps then be aware that these are specially rated parts for direct connection to AC.

    The filter is definitely required especially at a shared site to reduce both conducted and radiated interference.

    In either case this is not the classic 'Onan fireball', so the 230 VAC observation is not shot down just yet.

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    Anyone got any points on fixing the later model Motorola PSUs?

    I've got a dead one here that i'm avoiding fixing