Hantarex polo 25 h amp adjustment pot doesn't work

[frankrizzo2]

I'm working on on a Hantarex Polo 25 monitor and I can't get the horizontal size to adjust. I've done the cap kit already and I have replaced 2 Diodes next to the horizontal coil. The h amp pot is fine because I swapped it with the contrast pot and I'm still getting nothing for adjustment. There's not a ton of info on these monitors so I'm just putting some feelers out there to see if anyone has had the same issue. Thanks in advance

[lilshawn]

if it has the remote board... the cable where it attaches onto the chassis often break solder joints. maybe one is broken there.

check T118 it is a BDX53A
check T117 it is a BC5588
check D134 or D135 being bad

[frankrizzo2]

I plugged the remote board directly into the chassis because I thought the same thing but I'm still getting the same result. I replaced diode 134 and 135. I've also checked all of the bigger Transistors with the tester and they have been fine. I replaced 1 resister that was open last night but still no luck. I'm thinking that it is one of those rectangle capacitors close to the horizontal coil but I haven't had a chance to test those yet.

[lilshawn]

the "solid" type of capacitors don't typically fail. (ceramic, mica, etc) even after 40 years they are still good. the solid tantalum ones popular in the 90's don't usually drift out of spec, they just fail.

the electrolytic ones quickly go out of spec. the electrolytic capacitors have a usable lifetime measured in HOURS not years.

I think at this time if it still has it's original capacitors from factory, it's time to swap them out. check out "bob roberts" page for links to kits you can buy that have instructions and all the caps you need.

[frankrizzo2]

Well so far I've replace all of the electrolytic capacitors (Cap Kit from Bob Roberts plus I've replaced the 2 larger caps on the power supply), I've replace the HOT, T117, T118 and Both D134 and D135, swapped the h amp pot with a working pot and I've still got nothing for Horizontal Size adjustment. I've got a new flyback here but the one that is in it seems fine so I wasn't going to replace that yet. Any other ideas? Most of the things that I've read about these monitors is that they are a pain to troubleshoot. 

[lilshawn]

they are a real pain in the ass. Hantarex wasn't real popular in north america because we already had a few manufactures of arcade monitors here...no sense importing a monitor made in italy, right?

it's an okay design, but different enough to make it hard to diagnose.

to clarify, when you sweep the H-AMP pot back and forth...it does nothing right? it doesn't wiggle the screen...even move a little.. move anything anywhere? just dead as dead?

[frankrizzo2]

I get no change, flicker, or anything with the h amp pot. I've wiggled the wires and connectors also as I've adjusted to see if I can get any movement or flicker from it that way. Nothing. I've even plugged it directly into the chassis to eliminate the possibility of a bad cable. I've done a continuity check between connectors on the chassis and have also tested continuity on the adjustment board. It's going to be something simple but finding the problem spot is the challenge. Thanks for working through this with me. I want to find the solution so it can be archived for someone else in the future.

[ed12]

sweep the pot while u measure the output of the lm383
it must "vary"

ed

[frankrizzo2]

Just wanted to let everyone know that I scrapped that monitor. It takes a lot for me to admit defeat on something like this but I checked so many components on there and had so much time in it that I finally had to quit. I ended up putting an lcd in my Rev X cab and it works great and looks great!! Thanks for all the help and suggestions. Merry Christmas!!