Hantarex Polo 25" Monitor Problem

[theHaMMeR]

I just picked up an original Ultimate MK 3 that has a monitor issue. The screen stays mostly red all the time. You can make everything out just fine except for the constant red tint. When I tried adjusting the red gain and cut off pots it seems that the gain pot is not adjusting anything at all. So am I to assume that the pot is bad and I should replace it?? Also does anyone have a schematic for this monitor?? Thanks in advance.

[grantspain]

how red is the screen?it sounds to me either the drive transistor or the track/solder joints around it-its easy to trace from the gain pot and of course you should be concentrating on the neck card as that is where all the colour decoding occurs
i bet you get flashes of red as well

[theHaMMeR]

I get a pretty red solid background instead of black, and all the characters have a red tint to them, but I don't get flashes of red. The red gain pot on the neck card is where I'm not getting a response to the screen that's what makes me think it's the pot. I get color variances from the blue gain if that helps any. Thanks again.

[grantspain]

if the gain transistor is shot then your pot won't do anything,first thing to do is compare readings of the drive transistors if one is faulty then it will read different to the other two.
there are only three faults that are possible;drive transistor or feed circuit,the lm1203n decoder ic or a gun fault
a photo of the problem would help alot
if its a gun fault then you can prove that by disconnecting the red input from the pcb,if its a transistor/signal fault you can prove that by swapping the red and blue from the input of the pcb

[worm]

Just take the red transistor out and see if the problem go a way it should if not check smaller transistor.

[theHaMMeR]

Here are some pics of the screen, I would pull the trans. but I don't have a schematic for the chassis. Hopefully these help.

[grantspain]

i don't have the facilities to scan a manual but i have a neck card infront of me,the transistors you need to look at are t2 and t3 the former is the likely offender(its the bf859 with the heat sinc),the neck card has all the component positions marked so they are easy to find,like worm said remove transistor t2 first and see what happens.it looks like the transistor is skying it thats why your screen is awash with red,good luck

[theHaMMeR]

I pulled and tested both transistors. Both checked out fine. I replaced t 2 and the screen actually got redder. Pulled out the new one and replaced it with the old one. Anymore suggestions??

[SirPeale]

Could be a tube fault.  Had a K7000 recently that I thought was a cathode-to-heater short.

Well, after isolating the heater circuit to prevent that, I still had red wash.

Finally got our rejuvinator back, and I was definitely able to diagnose a short, but not what kind.  My best guess: cathode to cathode short.  Supposed to be difficult to remove, but I got it right away.  Monitor runs like a champ now.

[grantspain]

if you removed t2 completely and you still got loads of red then it would point towards a gun fault in the tube,i had the same happen on a sanwa

[theHaMMeR]

When I pulled t2 and checked the monitor I had no red color on the screen at all. So I replaced it with a new one and the screen was more red than the old one, I think I may have been given the wrong style after checking the BCE configuration. I tested the old trans. and found no faults so I put it back on the board and now its got a lighter tint of red. Could it be the IC on the neck card??

[grantspain]

yes it could be the lm1203n chip or the other smaller transistor at t3,basically now you have proved your tube is o.k so the the two mentioned components are the next logical step