Mitsubishi CS 3505 contrast issues

[Keith Park]

Opened up Big Bertha and changed out a few leaky caps and things
were better but I still have poor black level retention and the contrast control
does very little. Good brightness and picture otherwise.

Thoughts? Ideas?

Thanks

Keith

[zeno]

First off is that the chassis on 2 big boards side by side ??
If so there is a NP 'lytic cap in one of the power supplies (run)
that HAS to be changed. ( a chassis pix would help). It opens
& creates all kinds of havoc.

Besides that for now be sure you can turn the brite ALL the way down
with the customer control. If not look at the G-2 voltage and the
200 V (apx) source that runs the 3 video outputs on the CRT sockets.
Screen shots of real content may help us also.

73 Zeno
LFOD !

[Keith Park]

Its a single chassis board with the daughter board with Micro on the left hand side, and input board on the left rear.
I changed 4 or 5 bad lytic's, but still has poor contrast.

Thanks

[JohnCT]

Originally Posted by Keith Park

Opened up Big Bertha and changed out a few leaky caps and things
were better but I still have poor black level retention and the contrast control
does very little. Good brightness and picture otherwise.

Thoughts? Ideas?

Thanks

Keith

I have a note on an ineffective contrast control for that model, and the solution was to change a leaky C224 4.7uf/50v off Pin 37 Of IC201

The PIP module also causes issues, but generally causes vertical instability like bouncing or rolling well before getting so bad it affects the video. If the PIP module is the problem, there are about a dozen surface mount can caps that are bad. I used to replace them, but the leakage from the caps started affecting the traces as the TVs got older, so we used to just bypass the module with the customer's consent since the fad of PIP had passed. If you need that mod, I'll post it.

From my bible of old Mitsubishi repairs related to video issues in general:

C232 10/50v
C233 3.3/50v tantalum
C623 470/10

As those TVs got older, we developed a "kit" of caps to shotgun when they were on the bench to prevent callbacks:

C4f3 100/50v,
C4e5 100/35v,
C928 1000/50v,
C926 1000/35v,
C914 470/50v
C916 10/100v (Use 22/100v),
C206 470/16v,
C623 470/10v (Near Ic201)

These addressed several unrelated problem areas.

John