1980 Midway's Galaxian Issue

[Nimrod]

Hello all,
I have a 1980 Bally / Midway Galaxian Cocktail unit that is experiencing some troubles. The picture looks great and runs well for 20-40 mins or so after powering on, but then the screen will start to fade and grow dimmer over the course of 30 seconds or so, and then goes totally dark. The game audio continues to play blind in the background and everything else seems to run okay. When I first started working on the unit I found and replaced a blown tube fuse down on the transformer
board.

Not sure if this sort of issue is caused by a bad CRT tube, or if one of the nearby boards would be more likely to blame. I have looked everything over and did not find any visual problems I could identify; caps all look good, no scorching near any resistors. The CRT is an 'Electrohome 19" COL GAM MNT', product number: 38-G07904-00. Thanks in advance for any help or advice, I'm somewhat new to working on arcade cabinets and old tube TV's so I appreciate your patience!

 

[jassin000]

I'm not sure which part of the chassis is specifically failing, but I'd be willing to bet money the issue is 100% the CRT.

 

[twistedsymphony]

Most likely capacitors or flyback on your monitor chassis.

capacitors can be complete junk and "look" ok.

lots of people service that model chassis, so if you're not up for doing a cap-kit and flyback yourself you send it out to someone to rebuild it for you.

 

[Nimrod]

Thank you both for the quick responses! I apologize for my lack of knowledge, specifically in the lingo department, so let me ask to clarify: When you say chassis, what part(s) are you specifically referring to? Is it just the glass tube & yoke portion of the monitor, the board that is right next to / below the tube with the flyback soldered to it, or the metal frame around all the other components, or all the above(as a PC tech guy, chassis to me means "case" or "frame", but that does not seem to be accurate here).

Going deeper in, I took the circuit board near the monitor out of the unit and inspected it a bit closer, upon which I found a resistor with heavily corroded leads (the manuals part list has it as 'R1523', a 2w 6hm resistor). The leads were so bad one snapped right off while I was de-soldering it from the board. I have a replacement on order already since I'll need it, but what do you think are the chances are that said resistor is/was the problem? (Since you recommended caps as well, I'm going to go ahead and re-cap what I can on the board while it's pulled out, but replacing the flyback is outside my comfort zone)

Thanks again for any help or advice, and if some pictures may help let me know.

 

[jassin000]

Most CRTs contain two (potentially more if they use daughter/sub boards) PCBs.
One is attached at the back of the tube, often referred to as the neck board.
The other PCB is called the chassis, it sits below the tube and contains the flyback high voltage transformer (has a rubber suction cup looking end that connects to the top of the tube).

Hopefully I don't need to tell you the flyback generates a deadly high voltage, and it MUST be properly discharged before preforming any work.

Resistors that have failed often cause noticeable side effects immediately, caps on the other hand tent to still preform just not at the level they once did...
Creating a situation that becomes progressively worse with continued operation.
This of course is a very general statement, but I'd do as @twistedsymphony suggested and hit it with a full cap kit + new flyback.
If you can't/don't want to do it, discharge the tube and ship just the chassis to a qualified service person.

 

[twistedsymphony]

yes the "chassis" is the monitor's PCB.

the thing is these old arcade CRTs are big analog devices and most analog deices have a lot of capacitors.

and capacitors tend to start going bad after 10-20 years. As jassin said they'll fall out of spec, but another thing they tend to do when bad is act differently at different temperatures. So whenever there's a monitor that works fine for a while and then stops once it's warmed up (or the other way around, works poorly until it's warmed up and then works ok) it's generally an indication that some capacitors on the chassis are bad.

however the screen going completely black is usually an indication of a bad flyback or a bad horizontal output transformer (AKA the H.O.T.).

These are all things that tend to go bad eventually and will need to be replaced.

 

[Nimrod]

Great information, I appreciate both of your input on this. I will go ahead and proceed with a re-cap of the chassis and replace the damaged resistor. If the problem still exists after that is complete then I will probably have it sent out for further repair. Thanks for your time spent helping out!

 

[stj]

this sounds like an Electrohome G07 - the best monitor ever made.
there's a few variants, can you post a photo of the main board - left side.

the main failing caps on these are a couple of 10uf 160v or 250v caps - one on the neck board and one on the base near the rear edge.

 

[Nimrod]

Indeed, it is a G07 model.

 

[Nimrod]

Here is the chassis

 

[stj]

o.k. that's a regular G07 - notice the dark area in the center showing where it gets hot - i would check the soldering in that area while your working on it.

btw, it's 41years old and only just started failing - think about that next time you see someone with a dead Hantarex.

 

[Nimrod]

Just wanted to swing in and say thanks to the three of you once again. I got the replacement caps in today along with the resistor that was damaged, after replacing the parts and re-flowing / adding fresh solder to the joints near the two heat sinks everything seems to be up and working normally! The unit has been on for about 3 hours without any dimming or other issues, and everything just looks better now too. Seems like this is a really great community here. This experience has been quite fun and I hope to come across some more arcade units that need repair and if I ever need more information I now know where to look.

Thanks again!