The NEW Build Your Own Arcade Controls
Main => Monitor/Video Forum => Topic started by: Minwah on January 15, 2019, 10:49:48 am
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Hi all, long time no post!
In summer I got a cabinet which has an Electrohome G07. The monitor was working (although very hissy), but not the game so I couldn't test it fully. I cleaned up the monitor as best as I could, and replaced some parts as a precaution:
Cap kit
Flyback
HOT
Voltage regulator
R908
Adjustment pots (bar B+)
Checked the AC in voltage from the isolation transformer, set the B+ voltage, made the necessary colour / geometry / convergence tweaks.
I have only been running Galaxian on the monitor, and it has been working great (although still quite noisy). However I noticed recently with the game disconnected and the blank grey screen showing, there are some odd things going on - a line down the screen, some flickering (dulling), and 'black' occasionally briefly appearing. Most of these things were not visible with Galaxian running, perhaps as most of the screen is black. These symptoms have got worse to the point that rather than being generally ok, it is now never ok. It's doing all sorts of things, probably best summed up by this video:
https://twitter.com/minsoftgames/status/1084945976434089986 (https://twitter.com/minsoftgames/status/1084945976434089986)
As you can see the grey/white that should cover the whole screen is either not present at all, or only partially there at times. It seems like perhaps something is failing?
Has anyone seen this before, or got an idea what I should check?
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It looks like your sync is not right. Have you double checked your caps for rating and polarity? Have you taken into account that C302 polarity is incorrectly marked on the solder side of the board? Is your video connected to the G07 correctly? Post a pic or two of things including your video connector. Galaxian is neg csync I believe so you should have the lower Red-Green-Blue-Ground-Empty-Empty and the upper should be Empty (or ground)-Sync-Sync. make sure you plug isn't off by a pin. Also you may be seeing some strange things because your screen control on the flyback is turned up way too high.
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Many thanks for your reply!
It looks like your sync is not right. Have you double checked your caps for rating and polarity? Have you taken into account that C302 polarity is incorrectly marked on the solder side of the board?
Yes to both. I will be taking the monitor out of the cabinet soon though, so will triple check!
Is your video connected to the G07 correctly? Post a pic or two of things including your video connector. Galaxian is neg csync I believe so you should have the lower Red-Green-Blue-Ground-Empty-Empty and the upper should be Empty (or ground)-Sync-Sync. make sure you plug isn't off by a pin.
Definitely connected correctly, with negative sync using the second 3-pin connector.
Also you may be seeing some strange things because your screen control on the flyback is turned up way too high.
I have turned the screen control up, because (in the video) no game is connected. The flickering bright white should cover the whole screen and be permanently visible.
Just to add - it has been working perfectly for 5 or 6 weeks, so I am sure everything is setup properly. It seems to me like something is failing (either a component or bad joint / connection?).
Since posting last, the 'white' part has gone permanently - ie no picture with the screen control in a normal position. The troubleshooting flowchart (https://www.docdroid.net/sz1Ix4g/electrohome-g07-article-and-flowcharts-by-randy-fromm-u.pdf (https://www.docdroid.net/sz1Ix4g/electrohome-g07-article-and-flowcharts-by-randy-fromm-u.pdf)) suggests checking X303 & X304, so will do so (& give the chassis a thorough check over) when I take the monitor out. Will post any progress once done...
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Check resistors R516 (150k @ half watt) and R517 (180k @ half watt). If either one goes bad, you'll have a darker than normal picture. If they both go bad, you'll have a blank screen. Usually when they go bad, they either radically increase in value, or they go open circuit. You have to unsolder those resistors to test them or else you get false good readings if tested in-circuit.
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Check resistors R516 (150k @ half watt) and R517 (180k @ half watt). If either one goes bad, you'll have a darker than normal picture. If they both go bad, you'll have a blank screen. Usually when they go bad, they either radically increase in value, or they go open circuit. You have to unsolder those resistors to test them or else you get false good readings if tested in-circuit.
Many thanks Ken. I will remove & test those when I take the chassis out.
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Check resistors R516 (150k @ half watt) and R517 (180k @ half watt).
Tested both of these - both ok (151k & 183k).
Also removed X303 & X304 - the latter tests bad. Will replace that and see what happens...
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Also removed X303 & X304 - the latter tests bad. Will replace that and see what happens...
Replaced X303 and X304 - problem solved! X304 had definitely failed but I replaced X303 too since I'd taken it out to test.