WG K7000 dead... flyback? (SOLVED)

[MKFan4Life]

Hi guys.  I have a WG K7000 series (K7197 to be exact) chassis that is in my Mortal Kombat 1 cab.  I recapped it about 2 years ago, but did not install a new flyback.

A few days back I was playing it for an hour or so and it glitched for a second and went out.

There is no neck glow and no high voltage whine I detect.  No static really on the face of the tube either, however, when you first power it up, I seem to hear static and high voltage for a second and then nothing, along with no neck glow.

I figured, time to replace the flyback, but also wondered if this might be high-voltage shutdown?  I checked the AC voltage coming in which is fine, and then the fuse which is ok, too.  I haven't removed the chassis from the tray yet, but when I do, I figured I'd check for shorted diodes at D19, 20, 21, & 22 (as I have read they can short) and then check for an open R103.  And then I would check the HOT also.  (figured Bob Robert's repair kit with the flyback, fuse, HOT, and a backup cap kit would be a cheap investment at $28)

Does this in any way sound more like HV shutdown?  The flyback has no visual signs of trauma I can see. 

A note:  This chassis was originally mated with another tube, a Zenith G-A63ADG25X and I paired it up with a different tube (the original had a bad blue gun).  The new tube was from a K7400 monitor and was a Zenith A63AGD01X.  They had close resistance on the horizontal and vertical coils, and it's been running great for about 7 months until now.  Just thought I'd include this info as some people say mismatched yokes and chassis types can cause problems.

Thanks for any insight.

[Sarver Systems]

I don't have an answer for you, sorry, but I am subscribing to this post because I have the same chassis that I just recapped, and it shuts off after about 5 minutes.

I am anxious to see what others have to say about your issue so I can hopefully track down my issues.

D19,20,21,22 and R103 are something I will need to check on mine. THanks for the info!

[lilshawn]

MKFAN: the place to start is your regulator...check to make sure you are getting B+ if it pops up and then shuts off, you'll have to check more into the system, it's shutting down cause it's overloaded (shorted cap or bad flyback)... if the voltage is not popping up at all (dead dead), it's gone bad on you and will need to be replaced...

SARVER: your regulator might be overheating causing it to shut down. check the thermal interface and make sure the regulator 1) bolted down good 2) grease is not all dried up yucky. (which can act as a heat insulator more than a conductor)

you could have a component going bad that increases in resistance before it loads down the B+ supply enough to make it shut off (overload protect)

BOTH OF YOU:

you must not run this monitor outside the cabinet. it needs to be isolated from the AC by the cabinet  transformer. if not, the monitor chassis blow up on you.

[MKFan4Life]

MKFAN: the place to start is your regulator...check to make sure you are getting B+ if it pops up and then shuts off, you'll have to check more into the system, it's shutting down cause it's overloaded (shorted cap or bad flyback)... if the voltage is not popping up at all (dead dead), it's gone bad on you and will need to be replaced...

SARVER: your regulator might be overheating causing it to shut down. check the thermal interface and make sure the regulator 1) bolted down good 2) grease is not all dried up yucky. (which can act as a heat insulator more than a conductor)

you could have a component going bad that increases in resistance before it loads down the B+ supply enough to make it shut off (overload protect)

BOTH OF YOU:

you must not run this monitor outside the cabinet. it needs to be isolated from the AC by the cabinet  transformer. if not, the monitor chassis blow up on you.

Thanks for the reply.  I will check that as soon as I get a chance.  The chassis has never ran without being connected to the ISO in the MK1 cabinet.   

[MKFan4Life]

MKFAN: the place to start is your regulator...check to make sure you are getting B+ if it pops up and then shuts off, you'll have to check more into the system, it's shutting down cause it's overloaded (shorted cap or bad flyback)... if the voltage is not popping up at all (dead dead), it's gone bad on you and will need to be replaced...

I checked for B+ at the large resistor (180 Ohm 25 Watt resistor) on the bracket the voltage regulator is mounted against (on the opposite side).  I have read that you can read each side of that resistor for input and output (B+).  It's reading 179.5 VDC on one side and 177.7 VDC on the other.  (ARGH!)

I know it's best to check on IC4 Pin 4 (positive lead) Pin 3 (negative lead) right?  Just so darned hard to cram my hand there and make good contact with the chassis mounted in place at the moment.

What do you think?   

[Sarver Systems]

I'm at the point now where I am 100% certain there are no solder bridges or cold solder joints. I also verified that all of the caps are placed in the proper positions, and in the correct orientation. I even went as far as reinstalling the old bipolar cap, since it was much bigger (but the same value) as the replacement.

I am able to keep the monitor powered up for anywhere from 1 minute to 10 minutes before it shuts off.

Sometimes I can even get through the calibaration screens, and even play a game or 2 before it shuts off. Other times, as soon as the memcheck is done, it shuts off.

I reflowed every solder joint on the neckboard, just to be sure.

My B+ is 119VDC until it shuts down, at which point it goes to 190VDC (if I recall correctly).

[Sarver Systems]

PS, if you want me to start my own thread (damn hijackers!), please let me know, and I apologize.

[lilshawn]

I checked for B+ at the large resistor (180 Ohm 25 Watt resistor) on the bracket the voltage regulator is mounted against (on the opposite side).  I have read that you can read each side of that resistor for input and output (B+).  It's reading 179.5 VDC on one side and 177.7 VDC on the other.  (ARGH!)

I know it's best to check on IC4 Pin 4 (positive lead) Pin 3 (negative lead) right?  Just so darned hard to cram my hand there and make good contact with the chassis mounted in place at the moment.

What do you think?   

6 to one 1/2 dozen to another. yes, you should have 2 different voltages on the resistor (the resistor blops down the voltage for the rest of the system that's why it's so honking huge)

that said, the B+ sounds a little off (should be somewhere around +120VDC on one side of the resistor and +145VDC @ the other side) try unsoldering one end of D10, this will disable the shutdown circuit...crank up the contrast and brightness (or black level or whatever they call it) and see if the monitor powers up then. (don't leave it too long like this, just verify it comes on.) if it does power on, quickly see if you are getting just a line on the screen. (this is why we crank the brightness) this means something else is wrong. if not the regulator is probably going bad and will need to be replaced. but you can try replacing C57 first...if it's still wonky replace the regulator.

My B+ is 119VDC until it shuts down, at which point it goes to 190VDC (if I recall correctly).

if that's the case, you could probably follow the same steps, but you likely have something going open and your B+ spikes up and the high voltage protection is kicking in. you may still have broken solder joint someplace. They can be super hard to see. the voltage looks good until it shuts down.

check the temperature of your horizontal output transistor and your vertical IC after it cuts off... something is conking out. there has to be a tell someplace.

[Sarver Systems]

Can you describe some steps on determining where those components are located? And how do I measure the temperature? Just touch them or with an IR thermometer? Am I expecting to find hot components or cold components?

[lilshawn]

Can you describe some steps on determining where those components are located? And how do I measure the temperature? Just touch them or with an IR thermometer? Am I expecting to find hot components or cold components?

all the components have an ID designation next to them.  i dunno what more i could tell you. search the board until you find the one you are looking for. the k7000 is pretty disorganized. so it's tough to find some of them.

 temperature can be measured any way you like. if you decide the "touch" method, i would recommend powering down first before touching. some of those caps have aluminium cases that are open on the top. they can carry hundreds of volts while it's operating. if you have an IR or thermocuple thermometer, take a reading sitting idle to get a base and then power it on and take your readings after it's failed..

failed components with either be hot or dead cold (depending on the mode of failure. Shorted components will be hot and failed open components will be cold.) yours still works, so i suspect your problem part will be hot.

parts will get warm, but failed parts will be OBVIOUSLY way hotter.

[Sarver Systems]

I guess what I'm asking is, what does the horizontal output transistor look like? A normal transistor? Something with a heatsink?

Thanks for answering all of my questions.

[lilshawn]

BEEP BEP!

[Sarver Systems]

Mine's a 7400, but I do recall seeing a component mounted to the heatsink like that.

[lilshawn]

ahh, see this is a different system all together. it's probably best you start your own thread. as this system is a regulated power supply

your board is a switchmode power supply. Totally different animal.

[MKFan4Life]

ahh, see this is a different system all together. it's probably best you start your own thread. as this system is a regulated power supply

your board is a switchmode power supply. Totally different animal.

I was about to press submit when my cell notified me of a reply to this topic, so you beat me to it lilshawn.  That K7400 is definitely a different beast.

I'll try to desolder that leg from D10 and reply with the results tonight if I can.  THANKS!

[Sarver Systems]

I already had one going, but I wasn't getting any replies. That's why I threadjacked this one.

http://forum.arcadecontrols.com/index.php/topic,135065.0.html is my original post.

[menace]

This is out from left field but if you can get your hands on an infrared camera you can spot a hotspot very easily.  I have revived many dead tv's, crock pots, monitors, power supplies by plugging it in, scanning for the hot spots and then starting there.  Had a 32" tv that just needed a .25$ diode to bring it back to life.

I had a k7000 with a bad thermistor (upper right of the board if flyback is in the lower left).  This caused it to power off intermittently...

[qrz]

typical areas are
C57  47uF/160v
C56  22uF/160v
R101  cold solder BOTH ends
C20,21  10uF/25v x-ray shutdown
R89 cold solder
and cold solder on IHVT , driver xformers and driver/output xistors
i have seen D10 fail ( 10v zener ). but, is rare

voltage on pin 5 IC 2  should stay low ...   

http://www.wellsgardner.com/pdf/Schematics/K7000_25_27_inch.pdf

[buffett]

K7000's also suffer from ALLOT of cold solder joints and broken pads.

check it all over good for any thing that looks bad and re-flow it even if it does not look bad.

if you pull D10 and the chassis works then your VR is bad.

if you pull D10 and the monitor is still in shutdown then you have other problems.

a new flyback is needed before you can have any known good place to start.

if you are in the US and need parts i have them.
if you need it fixed i can do it for you.

email me threw my site the arcadebuffett.com

Peace
Buffett

[MKFan4Life]

K7000's also suffer from ALLOT of cold solder joints and broken pads.

check it all over good for any thing that looks bad and re-flow it even if it does not look bad.

if you pull D10 and the chassis works then your VR is bad.

if you pull D10 and the monitor is still in shutdown then you have other problems.

a new flyback is needed before you can have any known good place to start.

if you are in the US and need parts i have them.
if you need it fixed i can do it for you.

email me threw my site the arcadebuffett.com

Peace
Buffett

Sorry to bring this old thread back to life, but I am the original poster and life has generally delayed any work on this thing for 2 1/2 years or more.  (Wife had medical problems and a couple of operations right after I started this thread.)

Anyway, I started working on this same chassis again and after pulling it out with intentions of pulling D10 to see if it fired up, I quickly found a large resister (R97 I think by D16 and D17) that was loose in it's holes.  (Solder had completely cracked loose.)

I desoldered it and checked it to make sure it was still in spec and it was, so I reinstalled it with plenty of fresh solder.  I then went ahead and installed a brand new flyback, and tested the HOT while it was handy to take it out of circuit (aiding a bit in the flyback removal since they are both attached to that heatsink), but didn't replace it as it tested good and although I had a new HOT, I had no new thermal paste.

Also tested the voltage regulator (in circuit though), and reflowed almost the entire solder side for good measure.  Also tested all the diodes in the power supply section and compared readings to ones I found online to see if they were close (in circuit I admit).  All seemed good.

Installed the chassis back into the frame and fired the game up.  Seems to have gone into shutdown again.  Checked B+ and it read 181VDC on one side and 182.5VDC on the other of the large resister on the left of the voltage regulator heatsink.

Next step tomorrow after work is to indeed remove D10 this time to see if it fires up, but until then, while I was at work I thought you guys might chime back in with ideas if the D10 removal turns out to be a dead end.

BTW, Buffett, thanks for the advice back in the past on buying the Pace MBT 250 (I'm TortureBot on YouTube).  Messaged you recently about that connecting rod that broke in mine the first time I used it (darned Ebay, lol!).  I bought a new part and fixed her right up, along with a new glass tube for the SX-70 solder extractor. (It was chipped badly upon inspection, too.)  Works great at the moment.  I used your methods for the voltage regulator testing in circuit, but not out of circuit.  Looks like that's what I may be looking at replacing soon.

Any help is greatly appreciated guys!

[buffett]

Awesome, glad you found the part.

the PACE is a great tool to have.

look ALL over the chassis to see if you have any more cold solder.
the K7000 has a problem with it.

even if it does not seem like it needs solder, ADD some any way, it will not hurt.

pull D10 and see what you get.

let us know.

email me if you need any other advice or parts.

Peace
Buffett

[MKFan4Life]

Awesome, glad you found the part.

the PACE is a great tool to have.

look ALL over the chassis to see if you have any more cold solder.
the K7000 has a problem with it.

even if it does not seem like it needs solder, ADD some any way, it will not hurt.

pull D10 and see what you get.

let us know.

email me if you need any other advice or parts.

Peace
Buffett

I know this is an INCREDIBLY old thread, but came back to this old machine and the problem with it's monitor after a few more years, lol. Been SO MANY things happening in my life since I had time to work on my arcade machines, but I'd like to keep all of this in one thread since it pertains to the same monitor and it's repair.

WELL, when we last left this K7000, it was in high voltage shutdown. I had replaced the flyback, (at the time it had been recapped a few years beforehand), and I had done a reflow. After Buffet and a few others had helped me along, I was ready to pull D10 to see if it would fire up. Well, a day ago I did that, and what do you know! It is working! So I turned it off after a brief check of the B+ on R301. I got a reading of around 167V on one side and about 154V on the other side.

I assume it needs a new voltage regulator, IC4, (from everyone's advice and flowcharts I've seen), and I have that part ready to install. I did check it in circuit, and I observed one short between I think the 3rd and 4th legs of that IC, STR30130.

The problem holding me up now is that I damaged the zener diode D10. I am generally extremely careful, but at the factory, they covered half of D10 with glue where they had sloppily coated the pot to adjust the HV shutdown circuit. I burned away a bit of the glue and thought I had the diode loose, but as I was pulling one leg up that was desoldered, it broke in two.

Can anyone tell me the specs for that diode D10? I appreciate it. And mods, if I need to start a new thread, I will. Just thought this was a continuation of the original repair, but I can edit this to point to a new post or something, in case someone digs this thread up and it ends abruptly.

Thank you.


EDIT: Just saw QRZ earlier said it is a 10V Zener for D10. Anyone have full specs? (Current/Power, Etc.)

[grantspain]

On a k7000 d10 is not a zener, its a 1N914b - you could use a 1N4148

[MKFan4Life]

On a k7000 d10 is not a zener, its a 1N914b - you could use a 1N4148

Thank you! This is definitely not what I was previously told. Found the schematic for the K7000 series and I see, as you state, the symbol for D10 is not a Zener, and the value I was told was wrong. I think there was confusion between D12 and D10, as D12 is indeed a Zener and at 10V.

Funny thing is, I have come across a 1990 article where Randy Fromm states to do the leg-lifting trick with D12 on this K7000 series, but I constantly hear (and SEE on his K7000 flowchart) to do this with D10. Oh, here's a link to the 1990 article: https://www.epanorama.net/sff/Video/Products/Servicing/Video_Servicing_-_Troubleshooting_Horizontal_Deflection_Failures.pdf

Upon looking at the schematic, I guess either would work, as D10 looks like the input voltage and D12 looks like the output (connected to the wiper of the pot for shutdown). So kill the input OR the output, and you kill the circuit, right?
 

[grantspain]

D10 will disable xray protection, not sure if doing the same to D12 would have the same affect

[MKFan4Life]

One more question. Everywhere I look I see that R301 is supposed to be 220 Ohm 15W. My chassis has always had a 180 Ohm 25W there. Worked for several years, but I can't see anywhere that says a 180 Ohm can be used there.

Heck, even Mouser at the moment doesn't appear to have an exact replacement for what is recommended. Ebay, I only found one at 50W. (There are some through-hole versions, but only one chassis-mount style.)

Your opinion?
 

[grantspain]

does it have another resistor soldered underneath

[princess prin prin]

180 ohm 25W is used sometimes, for instance in the medium resolution version:

https://usermanual.wiki/Document/AtariMonitorTM3211stPrintingWG19inMedium19K7635.449281281/view

[MKFan4Life]

does it have another resistor soldered underneath

No. Just the one. It hangs off the side of the large heatsink. I desoldered one end to check it's resistance recently, and it was about 185 Ohms. (Got a funny low reading around 28 Ohms in circuit, likely due to something in parallel with it, so wanted to check for sure.)

[MKFan4Life]

180 ohm 25W is used sometimes, for instance in the medium resolution version:

https://usermanual.wiki/Document/AtariMonitorTM3211stPrintingWG19inMedium19K7635.449281281/view

Never knew that. Maybe a tech had a 180 Ohm on hand and thought it would work in a K7000 series, long before I owned this machine/chassis.

[MKFan4Life]

Hey hey! Got the K7197 running! I replaced that diode, D10, that I accidentally snapped in half after an Ebay order for a 100 pack came in. Then I desoldered the voltage regulator (STR30130) and tested it once again out of circuit. Still shorted between pins 3 & 4. Tested the new one and installed it on the board. Put the whole works back into old MK1 and Whoohoo! She's running again.

I checked the B+ at R301 and it was around 172V on the input side, and 132V on the output side. Doesn't look perfect but damned close.

After adjusting a little, the picture looks really good. Nice focus and good brightness. I do see one anomaly. Some vertical lines on the left-hand side that are only apparent when a plain dark screen pops up. Just looks like 3 or 4 vertical static lines that don't quite cover half the screen. Randy Fromm's flowchart points to C57. Sound right to you guys?

I capped the chassis maybe 10 years ago, then when the HV Shutdown problem happened, the game sat from 2016 until now. The caps might have been older to begin with. They were from Bob Roberts, and lately I've seen some posts that his kits had aged caps to begin with. I know his site had stated he was once into various things (pinball, pool tables, jukeboxes, etc.) and had kept classic gaming parts and electronic parts, but I was never sure if his caps were being freshly replenished or were all NOS.

Either way, I likely need to go ahead and install a fresh cap kit in this one. Thank you to ALL the people here for helping! Now I can start my summer semester of industrial electronics with ---my bottom--- sitting where I am now on this computer in the morning! Lol! Nothing like learning to troubleshoot and build electronic circuits via computer! Damned Corona.