Wells Gardner 25 K7401 Not Powering On - Clicking Noises

john2654

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Wells Gardner 25 K7401 Not Powering On - Clicking Noises

I have a 1997 Mortal Kombat 4 arcade that works fine except the monitor. The monitor has power to it, but only makes a slight constant clicking noise. I think it is coming from the flyback. I don't see any neck glow. The transistors (Q503, Q504, Q505 NPN SANYO 2SC3782) on the neckboard are having the solder points coming loose off the board. I assume that they are burnt and bad. I will order 3 new 2SC3782 transistors and a cap kit. Do you think this will fix it?
Thanks!
 
The transistors (Q503, Q504, Q505 NPN SANYO 2SC3782) on the neckboard are having the solder points coming loose off the board. I assume that they are burnt and bad. I will order 3 new 2SC3782 transistors and a cap kit.

It's pretty common for those to get hot and come loose. Clean everything up and resolder them, they are not necessarily bad.

Do you think this will fix it?

Doubt it.
Check to see if the Horizontal Output Transistor is shorted as well.

These 7400's can be quarky when they start failing, kinda a pain frankly. IMO
Generally in the power supply section.
 
Yeah, I can't stand the U2000/U5000 or their replacements the K7400/K7500's. I have fixed one or two with a capkit that were going into high voltage shutdown (that's the click you're hearing)... but I've had probably a dozen others that I couldn't get them going again, I just can't wrap my head around how to fix them.
 
Yeah, I can't stand the U2000/U5000 or their replacements the K7400/K7500's. I have fixed one or two with a capkit that were going into high voltage shutdown (that's the click you're hearing)... but I've had probably a dozen others that I couldn't get them going again, I just can't wrap my head around how to fix them.

I accidentally fixed a K7500 by barely turning the B+ knob.

when I finally realized I was testing B+ wrong and got reads, they were in the proper range and the monitor never did the HV shutdown again. I never got a read on it when it was messed up, so... yeah. caps and random B+ pot adjustment fixed my problem.

I call it luck. lol
 
This series of monitor is REALLY finicky about its B+. Try turning down the B+ knob JUST A HAIR. Then try it again if that doesn't work.
 
Ok, I guess I will order a K7400/K7500 High Temp Cap Kit from Bob Roberts.

How do you turn down the B+ pot when they put glue all over it? Last time I tried turning one down, I broke it. I then replaced the entire pot with a new one and guessed its location and it worked fine.

Oh, and how do you order from Bob? I see he does not accept PayPal.

Thanks,
John[/QUOT

should be 120v's@ jumper {j12}
If 160v the set is in shutdown..
mention the P# on the board and the chassis #
The problem has nothing to do with the neck board..
 
I've fixed several 7400/7500's.

BTW - Randy Fromm has a flowchart for it, too...
 
Ok, I guess I will order a K7400/K7500 High Temp Cap Kit from Bob Roberts.

How do you turn down the B+ pot when they put glue all over it? Last time I tried turning one down, I broke it. I then replaced the entire pot with a new one and guessed its location and it worked fine.

Oh, and how do you order from Bob? I see he does not accept PayPal.

Thanks,
John

that's entirely how I did it. I happened to have another parts 7500 that WG didn't drop a glue jizzbomb all over it and was able to yank it out. the chassis I was trying to fix, they went apeshit with the epoxy, I spent like 2 hours trying to sand it off with my dremel to at least get the shit to come out of the solder holes. broke a few legs off things, including the B+ pot (hence the replacement) I wound up replacing a few other resistors and shit from that parts board as well... hooked it back up, and all I heard was this violent clicking.

I incidentally missed a solder joint on one of those yellow transformer boxes... oops. I didn't nuke anything, fortunately. filled it up, turned on.. it still shut off.

it was then I just turned the B+ pot a smidge, and it didn't shut off. tested it, it was at about 118V.

I don't know any other approach to removing the epoxy. :(

ask some more, eventually an answer will come up.

with Bob, you make an order, e-mail it, he'll give you a price, and then you have to mail him a check. he cashes it, if it clears, he sends you the goods. you only have to do this once. as easy as it sounds, I've never actually done it. lol
 
OK, I did a complete cap kit and replaced the transistors (Q503, Q504, Q505 NPN SANYO 2SC3782) for the neckboard and the flyback is still making the clicking noises. I managed to crack the glue off the B+ pot and tried turning it down, but it still clicks. I tired reading the B+ voltage (black to chassis and red to white ceramic thing) and it blew my multimeter. Did I test in the wrong spot? Where exactly do I test the B+ voltage? Any other ideas? Where is the Horizontal Output Transistor and how is it tested?
 
First picture has the spot where i put the red lead. Put the meter on 250V DC. Second pic is just another of the chassis. Third pic is my dead, crappy meter.
 

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Not sure what exactly you were measuring, bit if I recall Test Point 202 (B+) was way over in the general area I circled in this pic. Should be right about 130v DC.
 

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Not sure what exactly you were measuring, bit if I recall Test Point 202 (B+) was way over in the general area I circled in this pic. Should be right about 130v DC.

Sounds like he was measuring the B+ at the spot most monitors get tested at. Not sure why that would have killed the meter though (unless it just a fluke). Got a Harbor Freight nearby? They've got meters for a few bucks.
 
Sounds like he was measuring the B+ at the spot most monitors get tested at. Not sure why that would have killed the meter though (unless it just a fluke). Got a Harbor Freight nearby? They've got meters for a few bucks.

One side of that resistor had some pretty high voltage on it, so that could easily blow an older meter...
 
Use the test point for B+. It's probably zero. If you want to get the reference voltage points from WG's support site, you can check some other voltage points to see what you have and what you don't...
 
Ok, I guess I will order a K7400/K7500 High Temp Cap Kit from Bob Roberts.

How do you turn down the B+ pot when they put glue all over it? Last time I tried turning one down, I broke it. I then replaced the entire pot with a new one and guessed its location and it worked fine.

Oh, and how do you order from Bob? I see he does not accept PayPal.

Thanks,
John[/QUOT

should be 120v's@ jumper {j12}
If 160v the set is in shutdown..
mention the P# on the board and the chassis #
The problem has nothing to do with the neck board..

Ok you were testing the wrong side of smps thats why you had 160v..
its the secondary voltages that you adjust J12 comes right out of the
power supply It need to be set at 120v's...use the vertical Ic heatsink
for ground..t202 is ok to test the voltage but its the other side of chassis
and you counld have an open trace,so i would test it as close to the powersupply you can..

First you always need to do and ohm check or diode check on the Horz transistor first
Q704 if it reads shorted replace it....this will save time,starting with the ohm meter first,it should be high ohms on all chassis.
Most of the time it shorts from colector to ground.
Check the ohms colector to ground..then let us know what you findout
 
OK, I replaced the HOT Q704. Still does the flyback clicking. I tested at TS 202 and there is no reading.
Thanks!
 
OK, I replaced the HOT Q704. Still does the flyback clicking. I tested at TS 202 and there is no reading.
Thanks!



Ok,no reason to replace Q704 if its not shorted,second did you find a short there
on the collector?All supply lines should read high in ohm's.Get that meter from HF
for $22. it's good enough.

check the voltage at D118 22v line out of power supply,if missing replace U101
you should have already replaced C117 from cap kit.
Others to check are R102,R103 68k for increased resistance..
U101 pin 7 should read 18-19 volts with hot {ground pin 5}...
if pin 7 reads 25-30v or better U101 needs to be replaced.
 
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