Hantarex Polo 25 Vertical Collapse

Jetkidish

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Hey Everyone,

I'm working on a Polo 25" with vertical collapse and it's been kicking my butt.
The monitor went into collapse, was left off for about 30 min, turned back on and worked for another 30ish minutes before going back into collapse.

Currently I've done the following;

Subbed IC104 and IC103 from another known good chassis
Checked R167 and R177, both test good in/out of circuit
Checked continuity down to the remote board, no issues, pots test good
Chassis was re-capped about 3 years ago, but has been running nearly daily. Just for fun, based on the flowchart out there, I went ahead and replaced caps C144, C142, and C137
Re-flowed the majority of the chassis, tested continuity between points and been looking for any signs of cracks in the board

I have 26 VDC at TP31

All of this and still no change.

Visually I don't see anything wrong on the chassis, R255 looks a bit toasty but still reads at 150 ohms.

Any suggestions on what to check next?
 
Open deflection coil once is warm up?
Just checked that now and the yoke tests fine, I've had a spare polo I just rebuilt today running on it for the last hour with no problems.
Meanwhile, the original chassis is still in collapse.

I'll likely comb through it and test traces/components, will update if I find the issue.
 
Does the chassis have two (insulated) resistors on the bottom side under the remote control header?
 
Measure resistance from pin 7 of IC103 to the V.AMP pot on the control board (the pin that is not grounded). You should measure about 100K which is the value of R170 (in line with this trace). If you don't, check the solder joints of the pot, of the header and look for possible hairline cracks on the main board in between the remote control header and IC103.

As for the resistors on the bottom, they're part of the US Polo design (they're not used on the European version I'm accustomed to). They're R256 (330K) and R258 (18K) in the US schematics. On later revisions they have a proper place and they're screenprinted as R257 and R258. They form a voltage divider using the -190V and +12V lines. The common point goes to pin 6 of the remote control header which is connected to the above mentioned line that controls the vertical size. From what I can see in your pic their solder joints look OK but double check that.

R256R258.jpg
 
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