Disco 19" with flagging - cap kit installed - need a diagnosis

[smalltownguy2]

Disco 19" with flagging - cap kit installed - need a diagnosis

I have a 19" monitor in a Super Baseball game that needs some attention. The tube is a Phillips 19VKUP-22, and the chassis is a Disco DMC Model 2090DT-2A. Manufacture date is 1982 -- this monitor was originally in an Atari Food Fight cabinet - in fact the cab itself is a FF conversion.

I've got some annoying flagging going on here, and would everyone's opinion as to what I need to do. I've already tried adjusting all of the vertical and horizontal pots -- this is the best I can get. I've already installed a cap kit, and no change.

Here's a video of the monitor in action:

http://www.youtube.com/v/YbQSbM8tdTI

 

[RetroHacker]

By "flagging", I assume you mean that the picture is waving like a flag? That's usually a failing B+ filter cap - it's the large one on the chassis, and not included in monitor cap kits due to it's cost and the fact that they're usually still good. But if the picture is waving like a flag, that's what I would look at. Of course, start by checking to ensure the B+ voltage is set properly...

-Ian

 

[smalltownguy2]

Okay, any ideas how I determine the value of this cap, and where to get a replacement?

I've found the monitor service manual here:

http://arcarc.xmission.com/PDF_Monitors/Atari Monitor TM-210 2nd Printing Disco 19in.pdf

There's a detailed component list, but I can't determine which cap is the filter cap.

 

[RetroHacker]

Okay, any ideas how I determine the value of this cap,

You could look at it.

and where to get a replacement?

Bob Roberts, Mouser, Digi-Key, Jameco, any electronic parts supplier.

I've found the monitor service manual here:

http://arcarc.xmission.com/PDF_Monitors/Atari Monitor TM-210 2nd Printing Disco 19in.pdf

There's a detailed component list, but I can't determine which cap is the filter cap.

Look at the schematic - it's the one right after the rectifier bridge, and just before the B+ fuse. Or, again, you could look at the monitor itself. It's the big cap.

-Ian

 

[RetroHacker]

Before going out and buying that cap - be sure your B+ is actually set correctly. Should be 115 volts. According to the manual, the B+ test point is A1, and the adjustment pot should be marked.

-Ian

 

[gregatron]

I would check B+ too as suggested but I honestly would try to full cycle the H and V hold pots a couple of times then readjust accordingly. Those Discos are a pain in the ass when it comes to the sync adjustments (in my experience anyway).

PS, the filter cap
is 470 uF @ 180V (or 200V)

 

[smalltownguy2]

Just for kicks, I'm going to try this monitor in another cab to see if the issue might be in the Big Blue in the power supply block in the bottom of the old Food Fight cab that this one's in. I have a Neo Geo cab available, and a Double Dragon Cab.

I'd like to hook this up to the Neo Geo cab just b/c it will be easier -- it's already opened up. The only thing is my Disco chassis only has the 6 pin header for RGB,ground, and positive sync. The additional 3 pin header for negative sync is not there I assume this is because Food Fight must be a positive sync game, thus the additional header was not needed during manufacturing of this chassis.

The Neo Geo video output feed goes to both the positive sync pins as well as the negative sync ones. Is there any way to hook the Neo Geo feed up to the monitor just to see if the picture is OK? If not, I'll try the feed from the Double Dragon cab I guess, it's just that the DD cab is a bit harder to get to right now....

 

[smalltownguy2]

I measured the B+ voltage, and I got 141v. Turning the adjustment pot did nothing. Double checked the pot's solder connections; they appear fine. Do I need a new pot?

I hooked the monitor up to the Neo Geo Cab, and fluttering on the top of the display went away, but I still get a slight 'wave' I've uploaded a video here:

http://www.youtube.com/watch?v=inmR2Dx_SzY

Problem with the filter cap? B+ pot? Both? I'm a bit stumped here.

Next step will be to hook another monitor up to the baseball pcb and see what I get for an image.

 

[smalltownguy2]

After a bit more consideration, I'm going to order a replacement filter cap. I have to get some more stuff from Digi-Key anyway, so I'll get the cap.

 

[smalltownguy2]

I replaced the filter cap tonight - made a noticeable improvement in color quality, I believe, but the 'wave' remains. What are my other options? Can the horizontal width coil cause this? It appears to be damn near broken off.

 

[smalltownguy2]

I've been looking at the manual for this monitor, and I'm going to start troubleshooting some components in the power supply and regulator section.

I have a question: the schematic shows Q002 and Q003 as 2SC1815, but the parts list breakdown shows Q002 and Q003 as 2SC945. I can't tell what they are on my PCB, as the letters are too faded to read. Can anyone verify what they are?

Does it matter which I use? I have a bunch of 2SC1815's handy on my bench, but I don't have any 2SC945's.

Thanks in advance...

 

[smalltownguy2]

I pulled Q001, Q002, and Q003, as well as Q901 tonight, all tested fine. Not sure what to test next.

 

[smalltownguy2]

Ok, I went back today and started over with troubleshooting. I wanted to see what the B+ voltage was once again.

Measured 142.6!! Too high. Adjusting the pot does nothing. Do I need to replace the pot, or could something else cause the voltage to not be able to be adjusted?

 

[KenLayton]

If that is what you measured and it was measured at the correct location with a meter with fresh batteries then shorted/leaky components in the power supply may be suspect.

 

[smalltownguy2]

Thanks, Ken, for taking a look at my thread. I pulled Q001, Q002, and Q003 as well as Q901, and those all tested fine. What other parts of the power supply should I be concerned with?

 

[smalltownguy2]

Sorry for dragging up an older thread, but I'm moving back to this monitor again, because I'd really like to figure this out.

Previously I'd pulled most of the components from the power supply section and tested them for shorts, and got no shorts. I've been doing some reading and it appears that some transistors may not test shorted on a meter, but still fall out of spec under load. Is there any way to confirm this without a scope?

If not, I think I'd rather just replace all of the components in the power supply section. As I see it, Q001, Q002, Q003, and Q901 should be replaced. What other components should I shotgun?

The monitor's already been recapped, and I've tested the B+ pot. Voltage is still too high at 142v. It's causing the image to be too wide for the screen. I can't adjust it with the Horizontal Width Coil, because the coil is broken and flopping around like a slinky. Initially I thought the broken coil was a problem until I learned that with my B+ voltage so high, I likely wouldn't get enough image adjustment from a properly functioning HWC to get the desired result anyway. I need to get the B+ voltage under control first.

I'm going to place an order with Digi-Key for the transistors I need, plus some other caps for a few other projects. What else should I get for this Disco so I don't need to order anything else?

 

[tevans333]

Silly question, but you are checking the B+ for DC voltage and not AC right? I've had my multimeter on the wrong setting before and it reads about 150 if on AC and will not change when the pot in adjusted. Also, if it is that high for DC, shouldn't the high voltage circuit shut down the chassis?

 

[smalltownguy2]

I was worried about that, so for kicks I fired up one of my Wells Gardner monitors and verified the voltage (auto ranging, auto meter) and it read fine and was adjustable. Back to the Disco, and it's fixed at 142, not adjusting. Testing the leads of the pot shows correct travel.

I'll double check to make sure it's reading the correct type of voltage.

 

[baritonomarc]

Did you check if the Flyback has some arcs? A little break in the flyback structure may give such a flagging effect. Turn the light off and visually check the area

 

[smalltownguy2]

I replaced the power regulator today (Q901) and no change.

I was in the middle of replacing the HOT (Q902) and I decided that I'd flip the board over to inspect it one last time to see if there were any cold solder joints. It was then that I noticed that C101, C102, and C103 are missing. Just empty holes where they used to be? I assume these were ceramic caps, but I'm not sure what purpose they serve. Those cap numbers do not show up in the schematics, so I guess I can ignore that for now.

Next up is to replace Q001, Q002 and Q003. That should pretty much cover everything in the power section.

No arcs in the flyback. That whole area looks good.

I picked up a Bob Roberts monitor width kit this week, so I'm going to attempt to dial in the width once I get this AC issue handled. Gotta wait until I get the voltage under control first though.