NEC 4FG

[Bob]

Hi all,

Here's a blast from the past.
I have a NEC Multisync 4FG which is giving me grief. Originally it had
the stock fault of height instability and collapse which was down to
the vertical caps leaking/drying out. It worked OK for ages but now I
get an intermittent set of lines/instability running up and down the
picture of varying widths. It doesn't appear to be affected by
temperature as I've tried copious amounts of heat and freezer to just
about everything. It also doesn't appear to be mechanicaly related
either. Sometimes it's fine for a few mins but then has a little burst
for a min or two, very annoying.

I've read just about every archive on the 4FG and similar reports of
vertical jitter/instability have always referred to the same set of
bad caps, which have all been changed.
Apart from changing every cap (not a good idea) has anyone got any
other ideas?
I would scrap it, but it's still got a very good picture (and loads of
my new caps in it!!) and I didn't want to beaten on this one.

Cheers
Bob

 

[Jerry G.]

I have one, and I changed every cap in the monitor. It works like new now.
It will never be like the ones of today, but it is good as an emergency
monitor. It was very expensive when new, even though it is a 15 inch.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================


"Bob" <bob@bfisk.demon.co.uk> wrote in message
news:c08b219.0402240421.33f8a029@posting.google.com...
Hi all,

Here's a blast from the past.
I have a NEC Multisync 4FG which is giving me grief. Originally it had
the stock fault of height instability and collapse which was down to
the vertical caps leaking/drying out. It worked OK for ages but now I
get an intermittent set of lines/instability running up and down the
picture of varying widths. It doesn't appear to be affected by
temperature as I've tried copious amounts of heat and freezer to just
about everything. It also doesn't appear to be mechanicaly related
either. Sometimes it's fine for a few mins but then has a little burst
for a min or two, very annoying.

I've read just about every archive on the 4FG and similar reports of
vertical jitter/instability have always referred to the same set of
bad caps, which have all been changed.
Apart from changing every cap (not a good idea) has anyone got any
other ideas?
I would scrap it, but it's still got a very good picture (and loads of
my new caps in it!!) and I didn't want to beaten on this one.

Cheers
Bob

 

[John Gill]

Bob:
I had a Mitsubishi that had light bars running up and down the screen.
It almost drove me crazy finding the problem. It turned out to be
a bad voltage regulator IC (a LM7808) on the CRT neck board. The output
voltage was good but very noisy.
Also check the electrolytic capacitors on the neck board, especially
those near the video amp IC.
Hope this helps....
John

 

[Bob]

Thanks for all replies guys.

I've just got myself an ESR meter so I'll check all the caps as a last
ditch effort.
Funny thing, checking some new 105c caps and their ESR was way over the
recommended value ie instead of approx 0.2 they were about 6. Possibly a
dodgey manufacturer?

Cheers
Bob

John Gill wrote:

Bob:
I had a Mitsubishi that had light bars running up and down the screen.
It almost drove me crazy finding the problem. It turned out to be
a bad voltage regulator IC (a LM7808) on the CRT neck board. The output
voltage was good but very noisy.
Also check the electrolytic capacitors on the neck board, especially
those near the video amp IC.
Hope this helps....
John