1220H as Replacement Chassis for MTC900/E

[mailman-zero]

I have an MTC900/E and I'm looking to get a replacement chassis since I want to finish up my current project (I'll go back and try to get this one to work again later)

Where I'm running into problems is trying to measure impedance to determine if the current tube is High Impedance or Low Impedance.  I have an analog multimeter and it seems that no matter what I set the sensitivity to, it always measures the same impedance.

Since the colors don't seem to match what the 8liners site says, how can I tell which ones are horizontal and which ones are vertical?


Also, it seems that my neck board has 12 pins and this seems to be non-standard.

I was planning on getting either the 1220H from Alva Amusement or something from 8liners.

Any help would be greatly appreciated. Thanks.

Edit: Upon closer inspection it appears that the yoke on the tube only has 10 pins even though the neck board has 12 holes in it.

[Ken Layton]

According to my repair guide for the MTC900/E, here are the readings:

Vertical: 15 ohm, brown and red wires are the vertical section of the yoke.

Horizontal: 2.5 ohm, orange and yellow are the horizontal section of the yoke.

This is considered a "low impedance" chassis for replacement purposes.

10 pin tube

Requires isolation transformer.

Wei-ya model 1220H is the correct replacement.

Remember that Hantarex did not use industry standard yoke wire colors nor connectors so you'll have to unsolder the original yoke connector wiring harness from the Hantarex yoke and solder in the yoke harness supplied with the Wei-ya.

[mailman-zero]

Thank you so much for your assistance, Ken! You da MAN! 

[mailman-zero]

My brand new Wei-ya 1220H monitor chassis arrived today and I got it all hooked up and these two resistors on the yoke burst into flames as soon as I turned it on. I think I had that look like Doc Brown lit the oily rags on fire with the model of the DeLorean.



So, what I'm trying to find out now is:
1. why did this happen?
2. how can I fix it?

I lopped off the "normal" wall plug and replaced the plug with the proper molex connector like the old one had, so I am using the isolation transformer (if that makes a difference).

I am at a loss. I hope I am not beyond help. Thanks.

[Ken Layton]

What's with the alligator clips? Are you certain the yoke wires are hooked up correctly? Is the yoke itself known good (no internal shorts or arcing between windings)?

[grantspain]

what wires of the yoke have you connected to where on the yoke plug,

[mailman-zero]

The alligator clips were connected to the correct wires for the horiz. and vert. from the monitor chassis. I didn't want to solder them on until I knew I had them right (in case the image was reversed or upside down.) None of the wires appear to be damaged, just the resistors.

As far as I know everything was working before. The monitor that was in there before displayed an image without blue, but its image was still stable (and no arcing).

Before ordering the new monitor I had trouble measuring the resistance with an analog multimeter in order to determine what type of replacement monitor to get since they all seemed to show only 2 ohms between each connection. That could indicate a short, but I never touched the yoke until after I tried the cap kit on the old MTC900/E chassis.

Is it likely that anything other than the 2 resistors are ruined? I just need to figure out where to go from here and what is safe to try.

Ken Layton and grantspain, Thanks for being so helpful. I don't know how far I would have been willing to go without your advice. Even if it turns out that this was all for naught I feel like I've learned a lot along the way and it has all been worth it!

[grantspain]

so you have the yellow and orange for the horizontal,brown and red for the vertical

[mailman-zero]

I mixed up horizontal and vertical because I remembered them wrong after looking at the board.

   I am usually a "measure 3 times, cut once" kind of person. I can even remember repeating in my head so I wouldn't forget "horizontal is the top 2 wires." Well, it turns out that vertical was the to two wires.

I can't believe I made such a stupid mistake. I reversed the connections I had and, against my better judgment, I turned the monitor back on and... IT WORKS (sort of).

The top of the screen is folding over and I can't adjust the screen to make it go away. While I was thus adjusting, I noticed white goo from the bottom of this solenoid:



I am assuming that's not good and that I should replace it. I'm guessing the fried resistors on the yoke should also be replaced (see earlier posts)... but now I can't tell what their values were, and all the old pictures I have inside the monitor are from angles that exclude those 2 resistors.

Would the resistors or the solenoid cause the folding over the top? I know it's hard to tell for sure what might be causing things like that.

Always a new problem to diagnose.

Thanks again for your feedback. (*trying not to feel embarrassed... and failing*)

[Ken Layton]

Those burnt resistors need to be replaced.

The white goo is merely silicone glue put there to support that heavy capacitor.

[mailman-zero]

That's a relief (about the glue). How can I figure out what the values of those resistors were? Is the total resistance between those two resistors supposed to be 15 ohm? Would a single 15 Ohm 1 Watt 5% Carbon Film Resistor between the 1st and 4th posts (from the left) take care of it?



Would the resistors cause the problem I'm seeing?

[grantspain]

peale has a 900 monitor,pm him see if he knows the resistor values
one resistor across 1 to 4 will not work
and those croc clips are crap,when you sort the problem do a proper solder job

[mailman-zero]

I know about the clips sucking.  It is taken care of.  I just had them on there temporarily 

Thanks for your help.

[SirPeale]

Those resistors might be an add-on.  I don't have them on mine.

[grantspain]

Those resistors might be an add-on.  I don't have them on mine.

where do your yoke wires attach on the yoke pinout,my guess is that this is an adapted yoke that mailman-zero has

[Ken Layton]

Aren't the yokes different between the 900 and the 900/E monitors?

[mailman-zero]

Aren't the yokes different between the 900 and the 900/E monitors?

Bingo. 

I have the schematic for the chassis, but I don't think it includes anything about the yoke (or its resistors). This information has to be available somewhere.

[SirPeale]

Aren't the yokes different between the 900 and the 900/E monitors?

I put a 900/E chassis on my 900 tube/yoke combo with no issues.

[mailman-zero]

What would those resistors control? Would they be the source of the foldover on the top? This seems like such a simple problem to solve, and yet... without information, I'm stuck.

[grantspain]

the foldover is down to something causing feedback in the vertical frame circuit
fingers crossed its just those resistors,if not then you may damaged the chassis
i would cut them off and see what happens

[mailman-zero]

Unbelievable.

I cut the resistors off and everything works perfectly!

Thanks for all your help. Sometimes the simplest solution is the most difficult to find.

[SirPeale]

Looks like those resistors saved your ass (as well as your chassis).