Hantarex Polo/2 28 15/25 Auto - Blows HOT

[infestus_bias]

Hi.  I have a few boards piling up with the same issue that I can't seem to figure out... blowing the HOT transistor.  With a cap kit, new flyback and new HOT, the boards will continue to blow out the HOT (the HOT is getting shorted out then overload clicking starts).

I've checked all of the components in the HOT circuit and cannot find a short.  My next effort will be to replace the C99, C101 and C103 polypropelene caps to see if that fixes the issue.

Any assistance would be appreciated if others have had the same sort of failures with these boards or if anyone can tell me what to check to trace down the faulty component.

Thanks!

[infestus_bias]

One of the boards is reading 190V on the B+ with the HOT removed.  Since the HOT blows immediately, the overload protection kicks in and I can't get a proper reading on the B+ or the low voltage circuits.  So I removed the HOT and it seems excessively high.  I'm curious if the B+ would be lower if the HOT were installed and working correctly?

I read 107V off of another board that's working for the B+ although I've seen on forums that Polos should be 138V B+.  The schematic shows 171V for the "Vb" & "Vc" and 105V for the "Va".  There is a "Switch Control Board" that Vb and Vc go into and come out "Vh".  Vh and Va both trace to the B+ supply, but I have no idea whether the Va or the Vh is supposed to be the B+ Voltage or what in that "Switch Control Board" is supposed to be doing

If it's fine to test the B+ without a working HOT, which I'm thinking it is, then what would cause the B+ to be so high?  The voltage from the bridge rectifier seems to be ok (ranging from 162 to 170 on the boards I've tested).

I also want to note that the Polostar schematic seems to be closer to what I have than the Polo/2 15/25 schematic that I'm using, for example my boards all use "D20" but it's NC on the Polo/2 15/25 schematic.  It is shown on the Polostar schematic.

[infestus_bias]

After looking at the schematic a bit more, I believe this "Switch Control Module" switches from Va for 15KHz to Vh for 25KHz.  I have to check my CRTs, but I believe they are 15KHz.  Therefore I should be seeing a B+ somewhere around 105V (in the example above, the working board read 107V on the B+.

If my B+ is reading 190V then something is very wrong, lol.  Either the Va is way out of whack or the Switch Control is malfunctioning.   At this point here are my questions...

1. Can I accurately test the B+ with the HOT removed?
2. Is there an easy way to troubleshoot the Switch Control Board?  Or perhaps to just force the monitor to be 15KHz as I have no need for the 25KHz?