Monitor Red Display Pentranic/Rodotron CH-281-38

[epicfatigue]

Hey All,

So a friend of mine got a mate to recap his arcade chassis, turns out he replaced a bipolar cap with a standard one.

I recapped the entire chasis with the correct values as i had no idea what had been done and wanted to start with a clean slate.

The monitor fired up perfectly fine for a total of about 5 seconds then the picture just went red, you can still see the picture but it looks like he red gain and drive has been pulled to max, and turning the pots does not appear to make a difference.

Its an Australian chassis i will find the model soon.

I am going to check the transistors on the board to see of any are shot, any other ideas?

This is not the monitor but this is what the picture looks like.

[mgb]

Yeah check the transistors on the neck board.
  This problem also can be a shorted gun in the tube.
Maybe try removing the red transistor and see how it changes.

[epicfatigue]

Hey thanks for your reply, going to check that for sure, i have tried the board on another monitor identical problem.

However if it is a neck board transistor surely these do no just go bad on their own, there would have to be a reason behind it shorting.
Or is this a common problem over time,

[mgb]

I don't know. I think the transistors do fail over time.
   

[epicfatigue]

hey got the chasis back today, tested the neck transistors no issue there all npns tested good.

Anything else i should be lookin out for will start testing all the other ic's we did smell some burning when it powered up. but not anymore and now red just appears to be stuck on

[buffett]

what chassis is it.

it sounds like it could be a tube problem.

Peace
Buffett

[epicfatigue]

wow very sorry everyone i thought i posted this in the top, it must have never sent (stupid internet)
 
Its a Pentranic/Rodotron  CH-281-38

Its def not a tube issue, as i have two of these monitors/chassis  same problem in both.
One of the chassis is working fine

I re capped them for a friend after his mate recapped one. The one that has the issue it the one his friend recapped. When i inspected it i found that he had put a normal cap in place of the Bipolar.

[ed12]

these are a perty straight foward chassic
they are much like g07-8's
your best bet is to ask rickn tuesday,as this is our long weekend
he is the eng of that chassic series
in another thread here u will find a 288 and it's cousin 289 pdf's
this will help u nail it down.
i would look at the 3 predrive trans on the main board
and or a lack of drive voltage to the neck board

ed

[mgb]

Have you gone through and resoldered connections? Maybe there's a cold solder joint.

[epicfatigue]

I have inspected them and there doesnt appear to be any, but i will scrub the board and reflow them all.

[epicfatigue]

I tested every transistor on the entire board none of them are bad. Will keep looking I'll pm ricken thanks ed

[Rickn]

This board was not meant to be used in a 38", but all that a side issue as it sounds like some one changed sweep caps to match the tube, Did you test the transistors on the main board? In this case the RGB comes in on the molex, then is fed over to the pre-drive transistors on the left side near the RGB controls, The the RGB is fed to the neck board via the cable. As you mentioned you checked the drive transistors on the neck board, I am thinking it is on the main board, Tried to zoom in on your picture, almost looked like a burnt component on the neck board. Been a while since we have worked on this board, when I get back to the shop I will check if we still have any and see if we have a hard copy of the schematic.

Rick 

[epicfatigue]

Hey Ricken,

thanks for popping in that is actually not my board its a picture from the internet, i can take a hi res of the one i am using.

I checked every transistor on the board which i was very surprised not to find a dead one as right before the issue poped its head up (20 seconds of a good looking screen) i could smell the wonderful IC burning smell.

So i checked PRedrive Neck and the Main board itself. and by check i just did the basic 6 step transistor check to make sure they were not Open or shorted.

Funny you mention that about the PCB because underneath both of these appears to be a modification a zenner and a few other things have been attached.
Will upload some decent pics tonight after work,.