25K7000 Missing Red

Peale

Active member
Joined
Sep 1, 2003
Messages
3,469
Reaction score
15
Location
Brattleboro, Vermont
I thought that I had a thread about this monitor already (well, I kinda do, but for another issue) but, I can't find it.

25K7000, missing red. Tube is fine (test tube). Neck transistor is fine. Swapped out the neckboard to rule that out.

Started tracing the circuit back from the neckboard connector back to the video connector. Didn't get far - when I metered R35, which should be 1K, I was getting 3.6 Ohms (in circuit). The other resistors for the other colours were giving me ~750 Ohms in circuit.

Pulled it, and it's reading fine.

Pulled IC1, and the resistors appear to be reading in-spec now. Strangely, the pin for red was bent at a weird angle. I'm going to install a socket, and see if a) a good connection fixes the red issue, or b) replacing it fixes the issue altogether
 
Success! I popped the original PC1397C into the socket, and the readings for the resistor dropped back to 3.6 Ohms. Pulled one off a donor chassis, and it was reading within spec of the other three.

Went to fire it up, and...RED! Well...kinda. On half of the screen. Then I realized that I forgot to replace the small capacitor that was bridging the two end pins (I think it's a cap, anyway, not an electrolytic, though) and once I did that, once again I have a fantastic picture. With all THREE colors.

I've been chasing this down for months, on and off. Didn't think that it would be IC1, I've never seen one go bad before.
 
Not a common part, is it. Not @ Mouser, or Electronix. Lots of datasheets on Google, but haven't found someone with them, yet.
 
Back
Top Bottom