Monitor buzzes

[Buddabing]

I plugged in my recently-purchased Galaga machine for the first time today and there's a loud buzzing noise that appears to be coming from the monitor. It worked at the warehouse, so I figure something is loose.

This machine has a pretty old monitor, which is connected to an isolation transformer. There are two loose connections that I can see. One is a 1/4" wide, fairly long connector which looks like it should be grounded, but isn't. The other is on the cable which goes from the motherboard to the monitor. It's an unshielded cable.

The monitor powers up and has a decent picture, it's just the buzzing that's the problem.

Any help appreciated. Please let me know if you need additional info.

Thanks,
Buddabing

[Ken Layton]

Are some of the screws on the monitor frame and metal brackets loose? Maybe something got knocked loose during shipping?

It's possible for the ballast on the fluorescent light fixture in the marquee to hum/buzz. Same goes for the isolation transformer in the bottom of the cabinet.

[MonitorGuru]

Couple guesses:

Your iron core broke free inside the flyback transformer. A common occurance after rough handling/old age.  To diagnose, take a paper towell tube and then point it directly at the flyback top (with monitor on) and listen on the other end.  If it is very noisy, move the end of the tube away from the flyback. if it gets less loud then it indeed is the flyback.

To fix:  With the monitor off, wedge some toothpicks between the shaft of the core and the surrounding plastic on the top of the flyback.  Turn back on and see if it helps.  If not reapply until you get it right.  Next to regluing with epoxy, that's about the best you can do.


Other guess: Your brightness and/or rgb drive [white level] and/or screen controls are too high and you're putting too much stress on the power regulation circuit.  (This is often seen with consumer grade cheap-o televisions when a solid white screen appears and the controls are still set at 'showroom' levels [aka 100% contrat, 100% brightness]).    If your picture bows outward when more bright images are drawn on the screne you have a week power supply circuit and could result in buzzing.    To diagnose: obiously adjust these down and see if it gets lower. To fix: check the B+ voltage and replace the caps (like the main filter cap) in the power circuit.

[Buddabing]

I did a few more tests......

1) The red gun on the monitor is out. I don't remember it being this way when I turned it on at the auction site, but I suppose it's possible.

2) I can't get the marquee cover off. There's a weird type of screw holding it on, it's a hexagon with a post in the middle of it, so that a normal hexagon-shaped screw won't work, it has to be hexagon-shaped with a hole in the middle.

3) I disconnected the speaker power and the monitor power, which left a soft, steady low hum which is coming from the marquee light.

4) When the speaker is plugged in, the loud hum comes back with an occasional crackle.

So I have two main problems, one being the red gun and the other being the speaker.

Some questions:
a) How should I get the weird screws out? Preferably without drilling
b) Is the low hum from the marquee light fixture normal? Would replacing the fixture help?
c) The monitor has some amount of burn-in, not noticable during play, should I just replace it rather than try to fix the red gun? My local monitor shop charges $80 for repair.

[menace]

for the screws i used a set of robo-grip pliers and manually turned them out--then threw them as far away as i could.  

The marqueee light hum is okay as long as its not too pronounced i.e. distracting--if so it may need a new transformer or starter--just go to home depot and buy one of their ready made units and plunk it in for 10$.  

As far as the red gun goes adjust the red controls and see if there is any change--also check all your connections--my green used to intermittently cut out and it turned out to be the wiring harness from the j-pac to the monitor-just a tap with a screw driver and it seated the wire more firmly.

you might also want to move your speakers further from your marquee light or get a shielded pair--might as well eliminate that hum while we're at it.

[MonitorGuru]

Red gun out: bad solder joint on the neck board, or blown transistor or bad red wire from game board to game (try swapping there first and see if you can use green to drive red into the monitor)

Marquee screw: Probably a "security torx" bit.  Check out your local dollar store or hardware store. THere are usually sets of 12-18 bits that have torx and allen (hex) bits to properly take out the screw

Light humm:  It's the ballast (aka transformer) not the starter.  You can get a new ballast at home depot but usally it's cheaper to just replace the whole fixture. Be sure you find one with instant on (one that doesn't force you to hold a rocker switch in a special position for the first second)

Loud humm from speaker:  Your audio may be turned up too high on the board?  Or you're getting 60 hz interference from the light and/or monitor.  Try placeing a noise filter on the game on the ac cord.  If not, look for loose grounds. Some (nintendo's mainly) have bad capacitors on the audio boards that cause humm, and even replacing those never fully fixes it. You can buy 12 volt automotive "ignition noise reducing filters" for car speakers and install them and they may help

Burn in:  Find an old compatable TV tube from a donor TV set and swap it in. May or may not fix the red gun (see issue 1 above).

[Ken Layton]

1) The red gun on the monitor is out. I don't remember it being this way when I turned it on at the auction site, but I suppose it's possible.
Is there NO red color at all or is the red 'stuck' ON all the time?

2) I can't get the marquee cover off. There's a weird type of screw holding it on, it's a hexagon with a post in the middle of it, so that a normal hexagon-shaped screw won't work, it has to be hexagon-shaped with a hole in the middle.
You need a "Tamperproof TORX T-20" bit.

3) I disconnected the speaker power and the monitor power, which left a soft, steady low hum which is coming from the marquee light.
Most flourescent light fixtures emit some amount of hum from the ballast transformer's frame. Check the ballast mounting screws for tightness. If they are tight, then replace the ballast with a new one (a 14, 15, 20 watt preheat ballast at Home Depot is around $4).

4) When the speaker is plugged in, the loud hum comes back with an occasional crackle.
Power supply capacitor & connector problems.

[Buddabing]

Is there NO red color at all or is the red 'stuck' ON all the time?

I reseated the connectors and the red is now working. The connectors are by no means snug, so it probably came a bit loose in transit.

You need a "Tamperproof TORX T-20" bit.

Where to get this? I'll probably try the vise grips first.

Most flourescent light fixtures emit some amount of hum from the ballast transformer's frame. Check the ballast mounting screws for tightness. If they are tight, then replace the ballast with a new one (a 14, 15, 20 watt preheat ballast at Home Depot is around $4).

Once I can access the marquee, I'll try that. I'd guess that it's a loose connection, if not, a cheap repair.

Power supply capacitor & connector problems.

Hopefully just the connector.  

Thanks all for the help, I'll post an update when I have one.

[Ken Layton]

As to finding the tamperproof Torx T-20 bit you can find them in those sets of screwdriver bits at Sears, Harbor Freight, sometimes even at Target.

[JoeB]

You can also go to Sears and purchase their special screw remover.  It's a handy thing to have if you loose the head on a screw.. it chews into the screw and gets it out.   Once it's out, you put a different one in.  I've seen commericals for it on TV and it works great!

[jerryjanis]

Security Torx wrench set (tamperproof): Bob Roberts has a really nice set for cheap:



http://www.dameon.net/BBBB/parts.html

It's listed on very close to the top of the page as "Security Torx Bits & Handle Special $7".

[Ken Layton]

That's an excellent price for that bit set!

[Buddabing]

Update:

I found the Torx tamperproof bits at Lowe's Hardware for $8.00. It didn't include the screwdriver part, it was just six bits that fit into a hexagonal screwdriver part.

So I took off the marquee and found:

The buzzing sound from the marquee is definitely coming from the ballast. The ballast is labelled "Radionics 14-15-20 Watt". Radionics has a huge array of ballasts, so I could get a replacement, the question is, will it do any good? It's a different environment going from a noisy arcade or warehouse to a relatively quiet living room.

Regarding my bigger problem, the nasty speaker buzz, I inspected the connections and they all look sound. I measured the resistance across the speaker terminals at 8.3 ohms, where I expected 8 ohms. Is this normal? Would a cheap 8 ohm speaker work if it was plugged in, or would the buzzing stay?

One interesting phenomenon: When I unplugged the marquee light, the game started without my touching the start button (it's set on free play). Once it started by itself, the control panel wouldn't respond until I pressed the start button. If I plug the marquee in and unplug it again, nothing happens, but if I unplug the machine from the outlet, plug in the marquee, turn on power, then unplug the marquee, this happens again. Is this related?

Ken mentioned a possible "power supply capacitor and connector problem" How to diagnose this?

TIA,
Buddabing