Blown fuse with Toei CM-F20U

[irocrt42]

I have a Mr Do with the Toei CM-F20U monitor.  When I turn on the game the sound comes on and the game works but the monitor doesn't.  The fuse (circled in yellow) is blown and is a 2A. The fuse just above the circle is 1A and below is 3A. I think this is called the isolation transformer but I'm not sure which part is the actual isolation transformer. ( I'm sorry if I sound like an idiot but I don't really know much about electronics. ) In the picture I circled one transformer? orange and another one blue. What is the one in orange and what is the one in blue? The green wire coming out of the one circled in orange is not connected to anything. Does this matter? Is the monitor causing the blown fuse or is the isolation trans causing it?  Thanks for your help.

[qrz]

more likely a monitor issue than an xformer problem. ( barring excess pri/sec leakage )

manual here : http://www.basementarcade.com/arcade/library/manuals/m/MrDo.pdf
 20" monitor on pages 29-30

 if f1 repetatively blows, then d24 bridge may be shorted.  f3 should go if a board fault

qrz

[irocrt42]

Thanks qrz.  I have a an operation manual but it doesn't nearly the amount of information as the link you gave me.  I removed the monitor board and looked for any signs of damage or loose wires.  The only thing I saw was a little bit of debris. A few small chunks of paper and or dust and a small slither of wood but no metal. Where do I go from here? Thanks for your time and help!

[qrz]

since the manual is a bit vauge on the fuse u indicated , lets replace the fuse .

then disconnect the monitor pwr and see if the fuse still pops upon pwr up .

if it does , its not the monitor .

print shows a smps with a fuse ref F1 ( page 27).  it is possible the fault lies here .
so also check d1,2 . q1,2 . c14 ( with power OFF-  )

qrz

[irocrt42]

Already tried that and the fuse does not blow.  Game still works but no blown fuses.

[qrz]

i took a closer look at ur pics . the monitor pcb does have 3 fuses on board. so , thats not it  .

i don't know what circuit the fuse in question protects .
so, will suggest attempting to follow the wire to its termination......

qrz

[irocrt42]

The wires going to the fuse?  The blue wire goes to the transformer I circled in in orange.  The other wire is red and it goes to the 100V TV outlet just below the yellow circle.  I hope these are the wires you were talking about.   I'm just a newbie on this stuff. Thanks again.

[qrz]

ok.....,so  that is the line feeding the monitor . ur doing just fine

disconnect the video line to the monitor and retry.
 if no blow , it is possible to be an xformer problem . ( especially if the monitor pwrs up on this test )
the only other possibility would be a degaussing issue . bad coil/thermistor. and they do fail .
however, that line is also fused ( 2a ) which "should" open if at fault..... could unplug the coil and retry ....

'dogs' can be so much fun 

qrz

[irocrt42]

Just now seeing your last post. Last night I went ahead and took the whole power supply out and took it to an electronic tech at work who said he collects a few game and pinball games. He told me to bring it in and he would test it. It tested ok. He told me to test  D24 (just like you said) which is a bridge rectifier.  I'm not too sure how to use a multi-meter but I think I did it right.  I got about a 3.5 ohms reading between one of  the ~ and + leg. And the same reading when I reversed the probes.  When I did the - and ~ I got nothing even after reversing the probes. I tried both ~ and the - and got no reading on both. I think this means it is bad?

[qrz]

yup, u have a shorted diode in the bridge.
replace it and with any luck , u should be good to go !


qrz

[irocrt42]

Thanks for all your help qrz. I will get a new bridge rectifier and put it in.  I will probably have to post back to get more help when I start on it.  It will be a few days before I can do it. Any idea on the specs for rectifier so I will be able to replace it with exactly the one thats in there? Also how do I take the old one off the board. Do heat the soder up with a soder iron and just remove? Any special precautions to take so as not to damage anything while I'm doing this? Thanks again qrz!

[qrz]

glad to assist....

i'd replace it with a 400piv / 3 to 4A  bridge .

be sure to observe proper polarity when installing   

radio shack has a cheap desoldering iron that should do the job for u .   40w iron w/squeeze bulb.
can use same tool to resolder if needed....


qrz

[irocrt42]

OK. I bought a 400piv 4A rectifier at Radio Shack. It didn't look exactly the same as the original rectifier. And the pins didn't match up to the holes in the board exactly.  I twisted the pins slightly and filed off a little of the pins since they were just a little thicker than the original.  I hooked everything back up and turned on the game.  Still no video but the same 2A fuse didn't blow nor did the the 3A fuse blow on the monitor board.  Should I not have used the rectifier since it didn't match or did I screw up somewhere else? Did I not solder good enough? Maybe not a good enough connection?  The piece of metal on the side of the board gets really hot. I will circle it red in the picture. The rectifier is right behind the power plug circled in yellow. I made sure I plugged everthing back in. I do "hear" the TV now though. The high pitch sound that a normal TV makes. Thanks

[qrz]

I do "hear" the TV now though. The high pitch sound that a normal TV makes. Thanks

the selected bridge should be ok . and i have no evidence of ur soldering skills to praise , or criticize 

the regulator is there on the left side . it will get warm. 
set now working ??
if not, are the crt filaments lit ? ( neck glow)
that will ( on most scan derived sets)  indicate a functioning horiz output stage.......

qrz

[irocrt42]

I don't know how else to describe it.  The sound that emits from a TV screen when its on but with the sound turned off.

[irocrt42]

There is no glow in the neck. I went back and resoldered one spot that I didn't think I did a very good job on but it didn't help. What is the black button on the metal frame in the pic just below the power in?  The service manual (that you sent me the link for) says its a Micro SW for demagnetizations. (page 13) What does that do? I think at some point I probable pushed it. Also, I forgot to mention a while back when I was trying to figure out what the problem was with the fuse, I plugged the monitor into a regular 120V outlet to see what would happen.  It blew the 3A fuse right beside the power in and the rectifier. The monitor is 100V so I don't know if I messed something else up doing that. Thanks again qrz.

[qrz]

that last little tidbit could mean a shorted regulator. if the HOT was shorted , u'd lose another fuse.

a regulator short would allow the set to start , but the xrp shutdown would engage ,disabling the
horiz drive.  there will be more to check....
back tomorrow

qrz

[MonMotha]

FYI, to answer your question about the pushbutton, that sounds like it turns on a built-in degauss coil.  This is used (hold for several seconds then release) if you have "rainbow" patterns caused by shifting magnetic fields.  Don't push that for now - it won't do anything useful and, if there's a problem with the degauss coil (happens sometimes), could just make your work harder.

[irocrt42]

Thanks MonMotha. I think I found some damage to the board. Looks like it got fried a little bit. I have before and after pics of when I replaced the rectifier and  it looks like there was a little bit of black before and now there is more. I think its around R103 and R105. Also I found another picture of someone elses Toei CM-F20U board and its the same way but a lot worse. The pictures are out of order. The first one is before, the last one is after. The board that is not mine is the second one.

[qrz]

ic6 is the regulator drive ic. ( la5112n)  which may be faulty . also check the pass xistor q301, and the hot (q401) for shorts.
this may be a direct result of applying raw 120vac.  all hot chassis's require line isolation......

qrz

[irocrt42]

Thanks again qrz.  I'm going to take the board out and take it to work and let the electronic tech test for the things you mentioned.  Don't know if this gives a clue to the problem or not but when I discharged the tube it didn't make a sound or anything. The last time the screen worked was 2001. I'll post back when the tech finishes looking at it. If he doesn't find anything wrong then I'm thinking about just going ahead and getting a new monitor unless you don't think I should just yet.

[irocrt42]

Thanks for all the help.  The guy I took it to at work couldn't find anything wrong with it so I just decided to get a new monitor.  I got one from Brady Distributing for $170.  Not even sure what kind it is.  Anyway, I know the Happ has a 19" on sale now for $135 but I just decided to go ahead and pick one up today and be done with it.  It was simple to put in. The only problem is colors on the screen in the upper right corner are a little bit messed up. Not sure what to do about it. Will take a pic and post later. Thanks again for all the help qrz!

[grantspain]

you need to switch off the machine for a few hours and then switch back on,it needs a degauss-which your monitor should do automatically at the next cold start up

[irocrt42]

Ok. Played Mr Do several times yesterday and it worked great except for the colors in the one corner.  This morning I turned it on like grantspain said to do to check and see if the problem was fixed.  The monitor didn't come on. BLOWN FUSE!!!!!!! Just like before.  So I plugged the monitor (a Kortek chassis with a 19" Samsung tube) in to another outlet seperate from the game and it works. The guy where I bought the monitor from said I could either plug it in to the same 100V outlet that the other monitor was in or any outlet.  Said it didn't matter about the voltage because it was designed to be able to work around the world.  He also said it didn't need an isolation transformer. Would it matter that I keep the game in my garage and it was pretty cool this morning?  Also, I remember reading somewhere about a power surge or something  having to do with the lighting on some games.  My Mr Do has a flourescent light behing the marque that doesn't work. Not sure if its just the bulb. There used to be another light on the back kindof between the back of the monitor and the top.  It had been removed before I bought the game. The cord is cut with some electrical tape on it.  I don't get it!

[grantspain]

either the fuse is underrated or you have some kind of short somewhere on the mains wiring
i reckon the fuse is a little low,how many amps is it?

[irocrt42]

Its 2 amps. I have pictures posted above of the power supply and the fuse is circled in one of them. Its the fuse holder in the middle. After I replace the bridge rectifier on the old monitor the fuse stopped blowing.

[grantspain]

i would try a 3amp,in the us you have a lower voltage so therefore the monitor pulls a little more amps,for example i have some ceronix that are marked 2amp 240v and 3amp 120v

when you switch the monitor on from cold it draws a little more amps as the degauss is starting from cold

the monitor onboard fuse will protect it from any problems chassis related