Hantarex polo star keeps blowing HOT

TimRose

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Hi guys I'm at the end of my tether with these monitors.

I have 2 chassis both with the same problem, they keep blowing the HOT, I have gone through 7 so far and darent continue.

One was fine until I forgot to plug the controls board in after troubleshooting a picture fault, I got the horizontal line on the screen and realised my mistake, so turned off the monitor, replaced the board and started it up again, not its popping HOT's for fun. Is this a coincidence as I didn't think leaving the controls board d/c would blow a hot.

The second one I haven't had working yet. After blowing so many transistors I have ordered the following parts,

New fly back, hot, safety caps at c100, c99 and c101, horizontal drive transistor and c92. Plus the four transistors on the switchboard as one tested out of spec.

Should these parts cure my monitor?

Can anybody point me in the right direction with these monitors? I'm new to the game but I'm confident with safety on monitors and not too bad at soldering. I can also read a schematic.

Hopefully someone has some experience with these monitors as I'm very close to grabbing a sledge hammer. Ha ha
 
O

obcd

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There a couple of 50V 1uf capacitors in the power supply section. If those go bad, the B+ voltage increases and that kills the HOT.

If you have a vertical pcb in the power supply cage, check the mosfets on that board. If the HOT goes, one of the IRF mosfets goes as well and due to that, the HOT goes again.

I had bad experience with a couple of HR DIEMEN THT's. One was giving me a vertical jailbar on the left of the screen and the other had a bas screen adjustment potmeter. The voltage became 2 high and the xray protection turned of the chassis. None of those killed the HOT. I also had once that a small capacitor on the base of the hot was bad. It also kept killing the HOT with that fault. It was on a hantarex EX3 chassis. (not a polo)

Good luck with them.
 
TimRose

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Thanks that's the sort of advice I'm looking for. I have ordered all for of the fets from the switch pcb in the psu as a precaution anyway, as one did test funny, so I decided to replace all four.

The caps I will check and get back to you

The cap you mention on the base of the hot, is that the safety cap? The one that's linked to ground? If so I have already ordered one of them too, so wahoo, at least I'm playing in the right area :)

Thanks for the input it's much appreciated, I hope I get this thing up and running soon
smiley1.gif
 
TimRose

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Just checked all caps in the psu and I do think have any 1uf lowest I have are 22uf 50v. One is the feedback circuit and the other is on the secondary side. Both check fine. So I should be able to eliminate them as problems?
However I did find 3 1uf caps on the switch pcb (the upright one with the mosfet on it?) And I won't even bother testing them I have just replaced them as I had some kicking around. As soon as the bits turn up I'll get it back together and give it a whirl.

Cheers
 
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obcd

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Maybe it's those 22uF 50V. It has been a while and I haven't exactly looked at the schematics before replying. Fact is, you don't expect those smaller capacitors to go bad, and you surely don't expect the impact they have. It's somewhere around the secundary section and it's close to one of the heatsink profiles. (A bit a pain to get the new one in the pcb holes)

If you desolder those fet's, they can act funny. If you measure resistance between gate and source, you charge the gate capacitor. Due to that, drain source becomes conductive and can be mis seen as a short. If you connect gate to source so that it discharges, drain source resistance will become infinitive again. (If the mosfet is good)
 
TimRose

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Near the heatsink is right :) pain in the arse to replace is also right :) it's been swapped ready, as have the small ones on the switchboard. I did find it tricky testing those fets, but one was definitely different to the others, so I just decided to replace all four.

Is there anything I should do before sticking power straight to it after all these new parts? Like turning the b+ down to minimum to stop it doing any damage until my meter clocks the reading? If that makes sense.

Cheers pal
 
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obcd

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Usually, I test the chassis B+ with the tube disconnected. I just load the B+ with a 40W light bulb and check if the supply does it's thing. As the link on the deflection coil connector is missing, the horizontal stage isn't switched on. Sometimes I do it with the hot removed as well just to make sure. A wire link between base and emitter of the hot also ensures the thing can't turn on. (Just make sure you don't connect the collector to the base.) One thing I had to do is turning the screen voltage down on the lopt as fully turned up, it can trigger the xray protection. If you didn't touch it, it should be fine.
 
Ordyne

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It is the 22uf caps in the psu, you are correct about it bring on the feedback loop, there's also another cap on the SMPSU IC, I used to replace all 3 of those caps regardless.

When I get to work I'll look at my repair logs but I'm sure everything has been covered so far. If you miss one of the bad components it will blow the hot instantly. Btw, what HOTs are you using? There were a bad batch floating around at one point of the original part and they couldn't handle above the specs of 15khz.
 
Ordyne

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Caps in the psu to always replace are C17, C18, C25.

T6 on the switching board is the usual one to go pop, IIRR some of them were IRF630 and some IRF640, always replace with 640's (check this, im only going from memory)

C101 is the poly cap that often goes bad with the HOT, always check this one

You should be ok with the2SC5144, it was the BU2530's that had issues but this was probably 5 years ago now.
 
TimRose

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So should I replace all the 630's with 640? Are they just a higher wattage identical fet?

17, 18 and 25 all have brand new caps in ready.

I have 2 chassis and both had these hots installed so I just assumed they were the correct ones, should they be something else? The schematic lists a totally different hot altogether.

Thanks for the help guys you have really boosted my confidence that I'm going to get it running :)
 
Ordyne

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tb2000 said:
I thought it was bu2727af for the Polostar (a number I've had/got have these installed), are 2sc5144 a better bet?
Click to expand...

You dont want to use a 2727AF on a polo star, theyre only 45 watt, you want 2727AW which are 125w

2sc5144 is even better at around 200w IIRR, these are also used in quite a few different chassis so its a good but expensive one to keep.
 
Ordyne

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TimRose said:
So should I replace all the 630's with 640? Are they just a higher wattage identical fet?

17, 18 and 25 all have brand new caps in ready.

I have 2 chassis and both had these hots installed so I just assumed they were the correct ones, should they be something else? The schematic lists a totally different hot altogether.

Thanks for the help guys you have really boosted my confidence that I'm going to get it running :)
Click to expand...

If you have already replaced them with 630's I wouldn't worry. IIRR hantarex started fitting 640's at some point, I think I might have some schematics that show an update to 640's but yes purely as they take a bit more stick!
 
tb2000

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Ordyne said:
tb2000 said:
I thought it was bu2727af for the Polostar (a number I've had/got have these installed), are 2sc5144 a better bet?
Click to expand...

You dont want to use a 2727AF on a polo star, theyre only 45 watt, you want 2727AW which are 125w

2sc5144 is even better at around 200w IIRR, these are also used in quite a few different chassis so its a good but expensive one to keep.
Click to expand...
Yeah I meant the AW version! OK so they're OK then, mind you I do have 2sc5144 (I think they're used on the 29e31s) also so it's handy to know they're fine also.tb20002016-08-25 12:12:08
 
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