Ameritron AL-572 loss of HV reading question

Discussion in 'Amateur Radio Amplifiers' started by N0OHL, Sep 7, 2020.

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  1. N0OHL

    N0OHL Ham Member QRZ Page

    Well, I was trying everything possible to avoid having to remove that Power Board. It will need to be at least partially removed to get to the Transformer Secondary wiring ( I believe ). And it looks like at least a dozen connections go to and from it that need to come off. Just to get a look at the wiring on the secondary side...
    However, it sure looks like it is probably a wiring problem from the transformer or the transformer itself...

    Since a fuse in back when out just before the HV dropped, I am thinking the transformer went bad? However I didn't smell anything --and the new fuse is still operating-- so Hope it may be just a wire ):

    I want to thank everyone esp. Chris for guidance with this situation. Hopefully it can be resolved at this point.... And would it be great if this set of problem determination instructions could help someone else(I bet it does )

    OK -- on to Power Board extraction ---- I think ?

    TXS Chris, W1QJ Roger WB2WIK
  2. W1QJ

    W1QJ Ham Member QRZ Page

    With the proper meters and measurements there is no need whatsoever to remove the PS PC board. There are plenty of test points to check for voltages that will either verify the transformer is good or no good. You’ll be doing work that may be totally unnecessary. You should easily be able to measure the secondary AC voltage at easy to access points.
  3. N0OHL

    N0OHL Ham Member QRZ Page

    Please let me know if I tested the wrong points? I checked the ohms between the HV RED wire against the HV RED/Yellow. Where else is there to check ---??? for Transformer connection

    Thanks in advance
  4. W1QJ

    W1QJ Ham Member QRZ Page

    There are two HV taps. Common is Red, then Red/yellow and Red/green. What did you read when ohming between Red and red/yellow and Red and Red/green and between red/yellow and Red/green? Just curious. Is there a way to gain access to pushing on the wires to test the soldering to the board? Maybe able to grab or push on the wire? Did you reflow the solder joints? It would seem that you read open circuit? Did you believe that the transformer was heated up badly? Generally transformers tend to short out not open, but it’s possible. What readings did you get st those wires?
    KD2ACO likes this.
  5. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    I'm using my chassis to demonstrate stuff. Yours is slightly different, but take a look at the measurement first.

    click on pic

    You want to measure resistance from the Red wire to the Red/Yellow wire and see around 13 ohms. Red to Red/Green should be about 9 ohms. If you measure 4 ohms between the Red/Green tap and the Red/Yellow tap while there's an open circuit between the Red and Red/Yellow taps, this would pretty much confirm that the HV secondary coil is open.

    If the connection is open, wiggle the wires a bit while measuring... push and pull gently to see if a reading pops up. I'm pretty sure that this won't happen at this point.

    Open equals, "Get a new transformer and install it." Alternatively, you could send the carcass back to MFJ and have them do it or have someone else install a new transformer if you don't feel up to that task.

    click on pic

    Some transformers have a terminal strip on them which would make it easy to determine if the open was a bad wire or if the coil inside is actually open. In my case, there's not much to do without extracting the transformer as the terminations are under lacquered paper and the secondaries are on the hidden side.

    Getting the HV board out doesn't look impossible but it also doesn't look like a whole lot of fun. This operation and the re-installation would need to be executed with precision and cleanliness to ensure a safely performed repair job.
    Last edited: Oct 1, 2020
  6. N0OHL

    N0OHL Ham Member QRZ Page

    Really want to thank you guys for all this extra help. I should have reported the reading from the other red taps in the previous post.

    They are all ZERO - OPEN. RED/YELLOW to RED/GREEN; and RED to RED/YELLOW or RED/GREEN all OPEN. SO what ever happened it shot the secondary. And as reported no signs of loose wires ( I did make sure I got a good connection for the readings) I pulled some -- but it appears I will need to dis-engage that HV/Power Supply board to get a look at the connections, but as Chris says the wires go under paper on the Primary side ( which I can see -- just like Chris's pictures above ) so I imagine they are the same on the secondary side. ( But will dive in and try and find out today )

    Gotta get one of those Fluke meters - do u like your 179 , Chris? RIMG0001.JPG RIMG0002.JPG

    Doesn't look ( what I can see ) if it heated-up.... and I haven't noticed any smell
    Last edited: Oct 1, 2020
  7. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Wow, what a bummer about the transformer...
    There is a Sanity Clause. Check the low voltage windings (Yellow and Yellow) to make sure the meter is working correctly. 2 or more blown open terminations including one that isn't being used just sounds very odd to me. As Lou pointed out, the usual winding failure is a short. I wonder what happened in there!

    I like the Fluke 179. It's probably overkill. There's a Fluke 115 in my go bag and I really like that one as a good meter for not cheap, but reasonable. The 179 is spendy. I needed the thermocouple option when I got it many years ago.

    edit: that listed price for the 115 is a bit high. I've seen them around for a buck-twenty.
    Last edited: Oct 1, 2020
  8. N0OHL

    N0OHL Ham Member QRZ Page

    Good suggestion Chris. to check the meter against the 12v secondary. All the yellow , yellow/black show about .5 ohms. I even measured each against the cabinet --- again .5 ohm. Guess that shows meter is working. So when ahead and removed one yellow from the board. It (yellow wire ) measures 2. ohms again the other yellow and the yellow/black and cabinet also-- which is a short?
  9. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    The low voltage supply works. I just wanted to see the meter work again before condemning a big transformer. That’s an odd failure.

    IME when a transformer fails, it’s from excessive heat and insulation breakdown. It would blow the mains fuse repeatedly.
  10. W1QJ

    W1QJ Ham Member QRZ Page

    I could easily see a red to /red-yellow or a red to red-green open, but a red-yellow to red-green open blows me away. I fix a lot of TenTec Titan 425 amps now that TenTec is gone and I have found at least 5 transformers shorted all in the same exact way. Obviously with all the failures being exactly the same there has to have been some sort of flaw in the transformer design. The short is always on the same primary winding. A PD replacement transformer is $800 plus shipping from Canada. I have designed a retrofit using the much less expensive Ameritron Al-800H transformers. I think the last time I bought one is was $246. Of course the PD transformer is bigger and heavier and can probably run legal limit rtty all day. The Ameritron transformer still provides plenty of soup for full legal limit power on SSB and on casual CW. The Titan RF deck works very well with the Ameritron transformer. It is thermally protected with a thermal cut out switch buried inside the transformer which Ameritron used to open the PTT line if the transformer overheated. You can't key the amp until the transformer cools off and the switch inside closes once again restoring the PTT line. When I install these transformers in the TT power supply I am not interested in doing all the extra wiring back to the RF deck to kill the PTT, but I do use the thermal switch contacts to fire off a small piezo buzzer I put inside the supply which will let you know that the transformer is overheated and not to use the amp until it shuts up. The entire retrofit is still less than the PD transformer cost.
    KD8DWO and KD2ACO like this.

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