INFO: Monitor missing green

[lilshawn]

I had a Big Buck Pro come in the other day...no green.

Tested transistors and all where good. tested computer output with computer monitor...all good there. hmm. maybe bad amp chip? (LM1202N) I'll dig up a neckboard and swap.

This monitor uses a weiya 666 chassis. (dual focus variety.) all i Had in shop was a regular single focus...swapped the tube sockets and a couple of resistors...

(change r231 from 10k ohm (Brown/black/orange) to 100k ohm (Brown/Black/Yellow) and remove R212A... R246 is different (3.3 vs 4.7ohm) but it's just for the heater and not a big deal.)

...to make the neck card work on dual focus tube.

still no green. change everything back. thinking tube is shot.

hooked up B&K 470 tester to tube (after i removed socket again and scabbed wired an adapter to use with the tester.)

set heater voltage 6.3 volts...okay
check heater to G1 leakage...nope, no leakage, good.
set G1 voltage to 50v...okay
set G2 cutoff +1 division for red...okay
set G2 cutoff +1 division for green... UH OH! no matter how high I crank up the G2 cutoff, the meter needle won't budge off zero.

well that explains it.

well the tube is garbage as it is, might as well gofro' broke.

Hit the clean/balance on the green go back and check... no change.

hit the rejuvenate on the green... For what we are about to see next, we must enter quietly into the realm of genius... blue/green sparking is evident in the neck tube. BWAH HA HA HA HA HA! Look! It's alive, IT'S ALIVE! Oh, in the name of God! Now I know what it feels like to be God! /evilscientist That wasn't quiet.

I test the emissions, they aren't great but better than some i've seen, WAY better than zero that's for sure. color tracking is right on the edge between bad and okay.

I re install the socket and fire up the duke...other than a very nominal tweaking to the color gains, it's back to normal looking.

we will run this one out for a couple of days to make sure it doesn't go sideways. I've marked the monitor so if it craps out again in the future, this was the one I had to zap.

TL;DR - green wasn't working on the monitor, turns out an internal short on the gun was causing the issue. A rejuvenation fixed it.

EDIT - I went all crazy clicky clicky before I even typed message  

[Gray_Area]

Good times.

[boardjunkie]

Just for the record, the LM1202/1203 is a high failure item.

[lilshawn]

Just for the record, the LM1202/1203 is a high failure item.

I think it's mainly due to the fact that the VGA input is fed directly to the chip. it makes the chip susceptible to static from even just touching the VGA connector.

[boardjunkie]

I don't think there's any MOS in that IC. I've seen 'em fail in the field from running hot.

[lilshawn]

I don't think there's any MOS in that IC. I've seen 'em fail in the field from running hot.

the lm1203 is...

ESD susceptibility 1 kV

the JEDEC standard specifies a 100 pF capacitor and a 1.5k ohm resistor used in testing. to simulate human touch discharge.

by simply protecting the inputs and outputs with an ULN2003, you could zap it with 30kV or maybe even 50kV no problem. and a ULN2003 is 1/3 the cost of an LM1203...hell, throw it in a socket and you could zap it, and replace it and be running again in 20 seconds.

[lilshawn]

well the green crapped out in this monitor again. the green is done for. 

you win some you lose some.