hantarex polo2 picture fault fix

[grantspain]

i am posting this fix here as it was such a pig to find,

today i had a hantarex polo2 go a bit strange whereas the picture would shoot to maximum width and there was no control over width,pincushion or keystone,the picture would also get distorted with a large pincushion bow

i ran the cab into the workshop and checked for the usual dry solder joints,found a couple suspect,re installed and for 10 mins it was fine then suddenly it jumps to full width

o.k i get the schems out and have look whats controlling the width,at first i am thinking maybe a cap so i take all the relevant caps out and test them-all 100% perfect readings

o.k next step look at the silicon components,check the diodes on the east west correction-hmmm,one of them is different to the schem-i download the data sheet and the spec of this diode is for a max of 16khz,ahah this polo2 is running at 25khz so naturally this ain't right,i install the correct value-things looking up i think

fired up the cab and now the picture is at max width with no control from power up-at this point i am thinking of giving up

o.k i don't like to be beat by things so i look again at the darlington transistor on the east west circuit and decide to change it as i have a few and this is where i find the other problem,the transistor is clipped to the heat frame BUT the insulation sheet is missing(this transistor needs one otherwise is shorts and cut out thus giving the large pic)i put in a new transistor and an insulation sheet and fire up,BINGO the picture is bit small on width but all the adjustments work

then i notice the width coil is screwed all the way out so i start adjust it and widen the picture,although i have to slightly readjust the pincushion

all i can guess is at some point someone else had a width problem and changed one of the diodes which would have caused problems then went on to change the transistor and left the insulation sheet off,i think where the heat sinc compound had badly corroded this had then given a temporary insulation to the transistor until the heat frame got to a temperature where the heat compound then became conductive again thus causing the original fault i had at the start of the day

i believe the original,original fault was just badly adjusted width coil which then took whatever tech down the road to balls up

i hope some of this helps anyone who gets a similar fault as it was a total xxxxxx,
if you read this and are now really bored then i apologize