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Author Topic: Hantarex Polo 25 Hot Keeps Shorting (SOLVED)  (Read 2471 times)

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jacamo

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Hantarex Polo 25 Hot Keeps Shorting (SOLVED)
« on: April 10, 2021, 07:15:56 pm »
Hello,
I was hoping to get some help from the likes of Greatspain or others that have wayyy more knowledge and experience in repairing these. I had received this from a friend as non working with symptoms of a bad flyback. I recapped it and and put in a new Flyback, and HOT. I went to test it and get the "ticking" sound of the Over current Protection Circut kicking in. When I test the HOT again it is shorted. I have followed the flow chart and replaced C172 as it tested way out of tolerance but no luck and I wasted another HOT. I am thinking now I should just go ahead and replace all of the HV caps in that area. 

I have also tested the Power supply section at L103 with a 40W light bulb and get 134V. So I have narrowed it down somewhat but was hoping someone could point me in some kind of direction. I have tested the diodes D134 & D135 out of circuit and they test fine. I have also tested the HV caps out of circuit with an ESR meter and all (except C172) were well within tolerance.
The only other thing I could think of is the Flyback I got was bad. It is one of the Chinese made ones but I know these are pretty rugged components.

Also would like to add that I have gone back through all of my work and double checked each cap for correct polarity and value. As well as reflowed every dodgy looking joint I could find and checked continuity on the traces that looked suspicious. I feel like I have covered everything that has already been mentioned on this site before but I am totally open to new suggestions.

Thank you in advance.

 
« Last Edit: April 27, 2021, 03:52:21 pm by jacamo »

grantspain

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Re: Hantarex Polo 25 Hot Keeps Shorting
« Reply #1 on: April 11, 2021, 05:28:08 pm »
where did you get the flyback from?
normally the HOT short will be flyback or hv caps or fake HOT, also double check isulation sheet of HOT is in good condition if using a metal case transistor

what bu transistor are you using?

btw best place to dummy load is centre pad of the HOT- remove the HOT first or completely isolate the centre pin

usa or european polo?

jacamo

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Re: Hantarex Polo 25 Hot Keeps Shorting
« Reply #2 on: April 11, 2021, 07:27:49 pm »
The flyback and cap kit I got from therealbobrobers.net
When recieved the flyback the metal bar holding the ferrite core was loose and had come off. I didn't think this would effect it though. I put it back and put some superglue on it just to make sure it wouldn't come loose again. Do you think this could have something to do with it?

I have the insulated BU508AF from Mouser

USA polo.

Do you think I should test it a dummy load on the collector? If I do this do any of the flyback pins need to be isolated or do I just hook up the load from Collector to ground with everything else as it normally should be?

Thanks

grantspain

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Re: Hantarex Polo 25 Hot Keeps Shorting
« Reply #3 on: April 12, 2021, 02:43:40 am »
i would imagine the flyback is ok if its supplied by him, what you did with the metal part is correct

bu508af should be full plastic package and therefore does not need insulation sheet but would require heatsink compound- Mouser are a trusted supplier so I would seriously doubt they would stock any fake components

test the b+ by dummy load on the collector, you do not need to isolate any other pins, you should get a good solid glow from the lamp and the b+ should read around 130vdc. You can also test your 16v and 24v

if all tests ok then remove lamp and use diode test to see if you have any shorts on the collector to ground

jacamo

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Re: Hantarex Polo 25 Hot Keeps Shorting
« Reply #4 on: April 12, 2021, 03:47:39 pm »
I didn't manage to test the b+ from the new point yet but I think I might have figuered out what is going on.

When you mentioned that the HV caps were usually the culprit I wanted to double check them again.

And of course now when I measure C174 is defantly out of tolerance. Measuring 4.7pf instead of 8.2nf on both my Fluke 87V and DE-5000

So I am going to make a mouser order and I will let you know whenever the parts get here. (shipping has been taking forever these days)

 

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Re: Hantarex Polo 25 Hot Keeps Shorting
« Reply #5 on: April 16, 2021, 05:01:36 pm »
I got the parts in from Mouser today and installed them.  I haven't tried to power it up yet as I had checked with the diode function from the collector of the HOT to ground and I am getting a beep in diode function.(This is with the HOT installed) When I use the resistance measurements I get about 1.5MOhm and it drops resistance.

Do you think this would indicate a short still somewhere? Also Do you think I should try and dummy load it before I actually try and power it on the tube?

Thanks

grantspain

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Re: Hantarex Polo 25 Hot Keeps Shorting
« Reply #6 on: April 16, 2021, 05:14:04 pm »
it should read like a diode, something like 0.480

jacamo

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Re: Hantarex Polo 25 Hot Keeps Shorting
« Reply #7 on: April 16, 2021, 05:39:08 pm »
Ok then It is reading fine.
Do you think I am good to try and power it up?

grantspain

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Re: Hantarex Polo 25 Hot Keeps Shorting
« Reply #8 on: April 16, 2021, 06:49:17 pm »
yeah go for it

jacamo

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Re: Hantarex Polo 25 Hot Keeps Shorting
« Reply #9 on: April 17, 2021, 07:43:10 pm »
Success!

I swear when I first pulled C174 it tested fine but I was thinking maybe after replacing C172  and trying it again might have finally been what caused C174 to fail.
Anyways I guess the moral of the story is REPLACE ALL THE HV FILM CAPS even if they test out ok.

Thanks for the help

jacamo

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Re: Hantarex Polo 25 Hot Keeps Shorting
« Reply #10 on: April 17, 2021, 10:32:48 pm »
Having never worked on one of these specifically I was wondering if you could tell me if this is normal to be displaying on the screen?

I have the jumper set to the Test Video

grantspain

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Re: Hantarex Polo 25 Hot Keeps Shorting
« Reply #11 on: April 18, 2021, 12:47:34 am »
yes if the test jumper is on
« Last Edit: April 18, 2021, 12:58:33 am by grantspain »