ws-55809 convergence

[rustamust]

I have a mits 55809 5 years old, had hour glass pic once in awhile tapped the heat sink and worked fine for weeks. 2 months ago bought stk392-570s from electronix and put them in on mon. TV would not power on so I rechecked things and found plug not seated, Tv powered on and had pic but the blue will not converge and is bow tie shaped. Removed board again and bought stk-392-570s from local dealer who assured me they are Sanyo at 29.00$ each so I put them in and checked all the fuses, powered on TV and still has non convergence of blue only in the bow tie shape. Can anyone please help with advice of how to fix or is my next option a mits shop??? This is not the same problem I started with but the same with both chips. Thanks very much.
Mike

[lcaillo]

You most likely have an open or cracked trace on the board or an open resistor.

[rustamust]

Thanks for your reply Icaillo, I was very careful with the board while doing work both times but will try to read the traces. The resistors I did a quick check and got a reading of some value with meter set on 2000K but not knowing the true value of the various resistors I'm not sure. When there was more than 1 ea the readings were the same. Can I read resistors on the board attached ? or should I just do continuity ? I did read traces from IC pins to first component solder joint. Is this problem new and not related to the 392-570s ? Once again thanks very much.

Mike

[lcaillo]

As I understand the scenario, you have changed the chips twice so it is unlikely a bad one. If you have one channel that is the problem (blue vertical only, from your description), you need to be looking for something that is unique to that channel. The best possibility is an open circuit on the output, but it could be an open between the convergence generator and the output IC or a bad convergence generator. You have likely either missed a connection or created a problem. At this point you need to be doing some real troubleshooting and signal tracing. If you don't have the skills for that and the schematic, you will need to get it to a professional.

[rustamust]

Thanks again Icaillo, This AM I pulled the board once more and went over the entire board with a magnifying glass and on the 4th pin from the left IC (looking at the board solder side) found a slight wrinkle in trace (Looked like it was there new) so I checked continuity and it was zero, then re-soldered, still no continuity, ran a small jumper wire across trace, soldered in place and installed board. It worked great, so buttoned up set, hooked everything up and turned it on and it still works, in the 4th hour now and just adjusted the convergence on all 4 inputs. Great pic and total cost $90.00 and I have a backup set of ICs. Thanks to all who posted there experience doing the same job which I used for guidance and most of all a big thanks to Icaillo for his posts

[lcaillo]

Glad I could help. It is easy to miss problems like that or to create problems when working with the boards. Usually when one channel is not functioning and the others are, it is an open circuit if the chips are new.