HP PL4260N plasma, sparklies after Y sus replacement

[DakotaKid]

The TV popped and picture went out but had sound. Y sus fs2 fuse was blown. This TV model seems to have a lot of common Y sus problems that cause this so I put in an identical Y sus board from a donor TV. It started up great but I now have sparklies, mostly red, in dark areas of the picture. I set Vs to 180V and Va to 180V on the power supply per the service manual. I set Vzb on Z sus to 100V, Vsc on Y sus to 120V.

-Vy measures -245V but should be -200V. However, it is at the maximum adjustment point so I can't adjust it further. I need help fixing -Vy and eliminating the sparklies.

Also, no visible damage to any boards or components.

Thanks.
DK

[tom66]

Re: HP PL4260N plasma, sparklies after Y sus replacement

It may seem strange but due to how those DC-DC boards generate the voltages -245V is too high, not too low. This usually happens when the feedback control is lost -- the potentiometer for adjusting it may be bad. Or, the capacitors can go bad too.

[DakotaKid]

Re: HP PL4260N plasma, sparklies after Y sus replacement

It seems this voltage problem could cause the sparklies and other problems, right? Would it be worth pulling the DC/DC pack off of the old Y sus board and replace the one on the current board with it? That would rule out bad pot. Or, any particular caps I should check?

I have a spare Y buffer and Z sus but thought I'd hold off on those until I get this voltage into spec. I don't know whether they would cause the sparklies anyway. About everything I know about plasmas is what I've learned from you and your writeups but it doesn't seem the buffer board would cause sparklies.

I am presuming the IPM is probably what blew on the old board but other than the blown fuse I haven't done any diagnostics on it as far as looking for shorts or testing the FETs.

The DC/DC packs are in the attached Y sus close up pic. I have labelled the Vsc adjustment pot and the -Vy adj pot and the outline is the -Vy DC pack on the Y sus board.
Thanks for your help Tom.

DK

[hienton2]

Re: HP PL4260N plasma, sparklies after Y sus replacement

I have just fix one PL4260N. I have VS 185v , va 60v . They do not match
with numbers on panel.

[tom66]

Re: HP PL4260N plasma, sparklies after Y sus replacement

If you can swap the module, I would recommend that. The high voltage can definitely cause sparklies.

[DakotaKid]

Re: HP PL4260N plasma, sparklies after Y sus replacement

I have just fix one PL4260N. I have VS 185v , va 60v . They do not match
with numbers on panel.

I just realized in my original post that I said 180V for Va whereas I should have said Va=60V and Vs=180V. Thanks for that catch. The panel says Vs=186V and Va=60V, the service manual specs say 180V and 60V.

Tom, I will try to swap the modules, going to be a challenge to remove them. They are similar to removing a tuner, two ground tabs and 8 pins to get unsoldered. It looks like both modules use Vs as input voltage. I see what you are saying about it being too high. I would suspect that Vsc DC pack scales 180V down to 120V and that -Yv DC pack increases it up to 200V and then inverts it? If this is true then maybe the -Yv DC pack is overdriving the voltage to about 255V because the pot only seems to have a range of about +/- 10V.

[tom66]

Re: HP PL4260N plasma, sparklies after Y sus replacement

The modules contain a transformer; they are fully isolated. This means the -Vy can be negative even though the module may produce a positive voltage. It just ties its positive output to the ground which creates a negative supply rail.

Vsc is used by the buffers to deselect a line. It is superimposed on Vs to create Vs+Vsc, around 300V, during the set_up ramp.

-Vy is used to select a line by the buffer boards. (Each deselected line is at Vsc; selected line is at -Vy.) The lines are selected during addressing to load data onto the plasma panel, before it is sustained. -Vy must be related in some ratio to Va but I don't know how. It's also used to generate the set_dn ramp. The set_dn ramp affects sparklies and maldischarge (like set_up.)

ALWAYS, always use the PANEL sticker for Vs and Va adjustment, and ideally the other voltages. Every plasma panel from LG & Samsung is manufactured to a certain tolerance, which means the voltage settings are different. Interestingly Panasonic use more precise manufacturing meaning only one voltage to adjust usually. I would guess this is due to the labour cost difference (Japan = expensive to have someone tweak five different pots / cheaper to more precisely manufacture panel, Korea/China = cheaper labour.)