NEC 4FG Problems

To correct pincushion problem cut path to wiper arm of vr403. cut path to pin8 of PWE 317E and run a new trace. This corrects the problem 80% of the time."also check associated electrolytics in this area as they commonly leak and cause several traces to corrode away. 

Thanks Walt and also John Holsepl, spot on, cap C561 was leaking: fortunately hadn't corroded the path as above, but would have eventually! But what a swine of a monitor to get apart!! or have I missed something simple?? I had to remove whole of front inc crt to get at board which I was just able to pull the required distance over to desolder and replace (with 100 degree replacement), Yup, it's a bear to do the R&R allright. Lots and lots of shields and screws. Removing the CRT & bezel assy is the easiest way.

If you haven't reassembled yet, check especially the two caps nestled near the LA7837 (trying to remember
from memory) heat sink, just about 1.5 inches in front of C561 you replaced. One or both of them is always bad.

Hi, > > has anyone come across this fault? It is outside adjustment range, The most common repair on a 4fg. C561. But change the rest too, if you aren't interested in doing the job again.

Pincushion, variable Caps on mainboard under PS leak on traces. brightness, or HV comes up Replace (all under
PS): only for a couple of secondC561 = 470uf 35v = CP-E47735 C556 = 470uf 35v = CP-E47735 C559 = 47uf 35v = CP-E47650 C557 = 1000uf 10v = CP-E10825 C562 = 220uf 16v = CP-E22735 C410 = 100uf 35v =
CP-E10750 C407 = 2200uf 35v = CP-E22850 C401 = 220uf 16v = CP-E22763 C404 = 220uf 35v = CP-E22763
C503 = 100uf 35v = CP-E10750 (near h-yoke connector) C555 = 100uf 35v = CP-E10750 Remove transitors &
transformer as necessary to clean traces with Flux-off and hard eraser. One or more traces will often need to be bypassed with wire. Ck. especially the trace under R556 & ZD554. Ignore my cap part numbers.

I have Nec 4FG and had a pincussion problem. I replaced the capacitors and the wires on the mainboard. When the monitor is on about a hour, the screen is suddenly brightly highlighted and disappears at all. With the highlighted screen the tube glows brightly. (Like a bright yellow light bowl). Try: C793 = 470uf 16v Located on L-shaped board next to CRT board. Leaks and eats traces. May or may not fix your particular brightness problem, but it has solved _some_ brightness problems for me. 

Regards, Al asavage@iname.com 