Tech: Hantarex Polo colour problem

[DanP]

[ukvac] Tech: Hantarex Polo colour problem
Hi All, I have a some point discussed the following issue with someone on
this list - I just can't remember who!

The issue is with a 19" Hantarex Polo monitor, the RED colour seems to be
having a problem. It's intermittently VERY red, and then sometimes devoid
of red. In the conversation I had, the person I spoke to told me this was a
well known and common problem with Polo's. Yes you've guessed it - I've
totally forgotten what this common problem was.

Any help/pointers much appreciated

Cheers

Danny.

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[Dave2084]

Re: [ukvac] Tech: Hantarex Polo colour problem
At 10:51 am 19 01 02, you wrote:
>The issue is with a 19" Hantarex Polo monitor, the RED colour seems to be
>having a problem. It's intermittently VERY red, and then sometimes devoid
>of red. In the conversation I had, the person I spoke to told me this was a
>well known and common problem with Polo's. Yes you've guessed it - I've
>totally forgotten what this common problem was.

I have this problem with my POLO, but with the green channel ... if there
is a solution let me know too!

Dave Langley
www.robotron-2084.co.uk

 

[Guests]

Re: [ukvac] Tech: Hantarex Polo colour problem

>>The issue is with a 19" Hantarex Polo monitor, the RED colour seems to be
>>having a problem. It's intermittently VERY red, and then sometimes devoid
>>of red.

>I have this problem with my POLO, but with the green channel ... if there
>is a solution let me know too!

I emailed Danny directly earlier, but I guess that there are a few people
out there who are going to have to repair these things, so here's a few
pointers from my experiences trying to keep about 20 of these going....

Intermittent colour is most often caused by dry joints on the tube base
board (give the board a prod with the handle of an insulated screwdriver
to see if you can provoke it into revealing the faulty component!). Most
often it's one of the three big power resistors or the drive transistors.

The power resistors themselves can also go intermittent which will result
in a screen that is flooded with one colour. Also the ribbon cable can
go open circuit, buzz it out with a multimeter.

Other memorable colour related problems with the Polo chassis...

If you can't seem to get the colour balance right (especially if you
can't adjust the black level down far enought to get rid of a colour),
then one of the BF859 drivers is probably breaking down under load.
Check the CRT drive voltage on the tube base, a bad BF859 will give a
reading of 40-80v. You can replace or swap with one of the other colour
drivers to confirm the problem. Beware that the transistor will read
good when tested out of circuit. This is a common problem, I now keep
half a dozen BF859's on hand because of this.

Flyback lines of predominantly one colour (after the black level has
been correctly set). The 74 series inverter on the main board near
the input socket is defective. You can snip the lead that outputs to
the affected colour, as it's only used for test pattern generation.
Don't remove the whole IC though, as I think that it is needed for the
sync circuit. This fault was a pig to find, it took me three hours to
track down, I'd even replaced the entire tube base board with a known
good one before I realised the fault was on the main board!

Hope this helps,

Dave.



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DATA Imported from archives: originally posted by Dave Roberts (daverob@cwcom.net)

 

[DanP]

Re: [ukvac] Tech: Hantarex Polo colour problem
Hi Dave, thanks for that. I had a looksie and reflowed the solder over any
suspect looking connections (including the connections on the neck board and
the big resistors) and voila! I now have a nice bright and steady colour
mix again.

Once again many thanks!

Danny.

SNIP!

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