Author Topic: Wells Gardner 25K7191 monitor won't turn on in NeoGeo (Read 9554 times)

MajorMarco · « **on:** August 25, 2011, 03:04:53 pm »

I have a Wells Gardner 25K7191 monitor won't turn on in my NeoGeo, when I turned it on the screen was blurry, playable, but all of the text was unreadable and definition in sprites was lost. I adjusted the contrast and brightness pots and made the system playable, however it seemed darker than regular. I started playing MS3 and about 20 minutes into the game the screen went black with that "dot" in the center of the screen like when you normally turn an old TV off. I adjusted the pots in an attempt to bring it back, but nothing...

I looked at the schematic and trouble shooting flow charts on this website: http://www.jstookey.com/arcade/WG_25k7191/ and I have replaced both the 2SD1398 and STR30130 semiconductors in attempts that it would solve the problem. No such luck.

We desoldered and checked C36 and it has a good capacitance before Q11 (Horizontal output).

Any other ideas what I should check or replace? I'm thinking the transformer could be the problem, but is there any good way to check it before buying a replacement? I don't have a high voltage multimeter or high voltage probes.

lilshawn · « **Reply #1 on:** August 25, 2011, 03:37:16 pm »

if it continues to display only a dot, i'd suspect a power problem. it sounds like you aren't getting any horizontal OR vertical deflection.

check your +12 volt line, you might find it's missing or really low.

MajorMarco · « **Reply #2 on:** August 25, 2011, 06:36:55 pm »

Quote from: lilshawn on August 25, 2011, 03:37:16 pm

if it continues to display only a dot, i'd suspect a power problem. it sounds like you aren't getting any horizontal OR vertical deflection.

check your +12 volt line, you might find it's missing or really low.

I think I may be giving you the wrong idea. There is no dot when I turn it on in the center. I only had the dot the once when it stopped working (similiar to when you turn off the monitor). The dot went away even while the machine was on.

I have checked the 12 volt line, it seems fine. But if you have any specific places I should check for the 12 volts, let me know.

srarcade · « **Reply #3 on:** August 26, 2011, 10:27:55 pm »

I'll give this a stab- anyone correct me if i'm wrong here, i'm learning myself.

Have you turned it on since? If you ever witness a flyback fail in front of you, its very much like what you described, but if you go to turn it on again, it won't power up. If it doesn't power up now after what you described, its probably because the flyback is done.

Checklist:
-you have high voltage (assuming it turns on still!)
-if you have high voltage, your horz circuit is working
-you had R G and B before it happened so your output is good
-you didnt have a rolling picture or scrambled eggs pic so your sync is probably good

So to me that narrows this down a little bit- vertical deflection circuit may have a problem?? But you describe a dot and not a horizontal line, so I'm thinking probably not. You have power, but I'd definitely check the voltage on the B+ first to make sure its within range. If your B+ is too high, it may cause something like you said possibly. If B+ is bad, could be a bad voltage regulator or shorted diode or transistor? Again- i'm not the expert, taking a guess.

MajorMarco · « **Reply #4 on:** August 28, 2011, 05:01:25 pm »

Quote from: srarcade on August 26, 2011, 10:27:55 pm

I'll give this a stab- anyone correct me if i'm wrong here, i'm learning myself.

Have you turned it on since? If you ever witness a flyback fail in front of you, its very much like what you described, but if you go to turn it on again, it won't power up. If it doesn't power up now after what you described, its probably because the flyback is done.

Do you mean "power up" as in the whole system? Or do you mean the monitor?

The monitor does not work, but the system turns on fine. I replaced the voltage regulators on the monitor already (mentioned on my first post), so is the next step to replace the fly back?

ed12 · « **Reply #5 on:** August 28, 2011, 05:57:37 pm »

hi
a few tip's here
1=do u have the b+ ie 130 vdc to the hot ??
2=isolate the chassic it is hot
3=chk the 130v to the flyback through the yoke
3=low voltage is not really a cause here
if u have the dc to the hot then it is not shorted and most lickley
nor is the flyback,but rather u have a drive stage problem
read the ken layton site >our fourm's<
if not just post back to me if u have the 130 i can and will walk u the rest of the way,just rem isotate this chassic for your saftey sake

ed

boardjunkie · « **Reply #6 on:** August 29, 2011, 11:05:54 am »

Check 130v B+ at the large resistor in the pwr supply circuit, not at the HOT/f-back. If the H circuit is running, the voltage spikes created by the switching can wreck yer meter. In fact, it says right in the manual/schematic "do not measure" at that point.

Just pwr it up and look for orange filament glow in the neck of the tube. If thats not there, then start chasing problems in the psu and H circuits.

MajorMarco · « **Reply #7 on:** August 29, 2011, 02:36:19 pm »

Quote from: boardjunkie on August 29, 2011, 11:05:54 am

Check 130v B+ at the large resistor in the pwr supply circuit, not at the HOT/f-back. If the H circuit is running, the voltage spikes created by the switching can wreck yer meter. In fact, it says right in the manual/schematic "do not measure" at that point.

Just pwr it up and look for orange filament glow in the neck of the tube. If thats not there, then start chasing problems in the psu and H circuits.

When the monitor was blurry, I opened up the back to adjust the brightness and contrast and the orange filament was glowing at the time, but when the monitor stopping working and I looked behind the monitor it was not glowing.

Just to make sure I understand correctly, should I be looking at the power supply unit for the entire Neo Geo? Or the power supply unit (circuit) for the monitor? I would think that if the power supply for the entire Neo Geo would be bad, that the whole system wouldn't even turn on.

I'm relatively new to repair of arcades, so please explain a few things to me. First, what or where is B+? Second, I presume the H circuit is the Horizontal output circuit, if not, please correct me. I have checked the capacitor for the Horizontal output circuit and the voltage, both were good. We have replaced the transistor Q11 for the horizontal output circuit as well.

I'll do the tests mentioned about when I have some time this week and report back the results.

Where do you recommend looking for problems in the PSU?

ed12 · « **Reply #8 on:** August 29, 2011, 05:01:48 pm »

hi
the 130volts we are talking about is the output of the voltage reg..on the monitor
best to chk it after the :power: resistor ,also known as load resister
so black lead of meter to ground red wire to either the str or the resister
set multi meter to dc range and if it id not digital autoranging
use the 200v scale
if u have 130vdc,then we go a tad futher

ed

boardjunkie · « **Reply #9 on:** August 30, 2011, 10:29:24 am »

http://www.100megspop3.com/jimbo/monitorboard2.jpg

See that white block mounted to the heatsink in the upper L corner? That is where you need to measure voltage. One side should be the raw B+ (which will be higher than the regulated output) and the other side will be regulated B+. This chassis uses the STR30123 (or 3123 if its the 4 pin version) so the B+ should be at 123v. Anything higher than that by more than a few volts will trip the HV protect and the H circuit will be shut down. So if thats the case, you'll have a dead monitor.

The regulator IC is a common failure on these 7000 chassis.

Before you go chasing that, check the fuse. If that is blown, then its likely you have a shorted horizontal output transistor(2sd1398)....another common failure. But....good news is they're cheap so its a good idea to order an extra to have on hand in the event of failure.

MajorMarco · « **Reply #10 on:** August 30, 2011, 11:50:28 am »

Quote from: boardjunkie on August 30, 2011, 10:29:24 am

http://www.100megspop3.com/jimbo/monitorboard2.jpg

See that white block mounted to the heatsink in the upper L corner? That is where you need to measure voltage. One side should be the raw B+ (which will be higher than the regulated output) and the other side will be regulated B+. This chassis uses the STR30123 (or 3123 if its the 4 pin version) so the B+ should be at 123v. Anything higher than that by more than a few volts will trip the HV protect and the H circuit will be shut down. So if thats the case, you'll have a dead monitor.

The regulator IC is a common failure on these 7000 chassis.

Before you go chasing that, check the fuse. If that is blown, then its likely you have a shorted horizontal output transistor(2sd1398)....another common failure. But....good news is they're cheap so its a good idea to order an extra to have on hand in the event of failure.

The link above sends me to a 403 Forbidden page. Apparently I do not have permission.

I have checked the fuse, it is good. I'm guessing I can track down the resistor and give it a check. What voltage should I see for the unregulated B+?

ed12 · « **Reply #11 on:** August 30, 2011, 01:05:24 pm »

hi
as a rule we use either the input dc cap rating as our guide
or u could google the reg and find it's max dc input
either is a good way to do it,but as pointed out
chk for dc on the output of the reg
str30123 is indeed a 123v reg
from what i read on the schematic the input cap is rated to 200vdc
so i would be good with 165 at the input to the reg
from what i read on the spec's max vin is 200vdc
but 165 is a good starting point

ed

boardjunkie · « **Reply #12 on:** August 30, 2011, 01:47:48 pm »

IIRC the raw B+ is around 140vdc. YMMV, but if you see the same thing on both sides of that 25w resistor, yer regulator is shorted.

boardjunkie · « **Reply #13 on:** August 30, 2011, 01:49:09 pm »

The pix link works for me....

MajorMarco · « **Reply #14 on:** August 30, 2011, 10:17:00 pm »

I have measured both sides of the 25watt resistor and have 173 volts on one side and 170.3 volts on the other side.

What should I replace or check next?

I noticed that one of the paper or cardboard sleeves (perhaps an insulator) that was somewhere on the board is not there anymore. It was on my table. It was between one of the transistors I replaced but I don't remember which one. It doesn't have any holes in it though.... I thought it would slip behind the transistor and the plate it gets attached to.

I appreciate your help guys on this subject.

boardjunkie · « **Reply #15 on:** August 30, 2011, 11:12:01 pm »

The regulator IC is shorted then. Replace it and it should fire up.

MajorMarco · « **Reply #16 on:** August 31, 2011, 12:12:59 am »

Quote from: boardjunkie on August 30, 2011, 11:12:01 pm

The regulator IC is shorted then. Replace it and it should fire up.

I performed a continuity check on IC4, and it seems ok, I did not get any shorts, but I also did not get continuity from pin 1 to ground like it shows. I'll check it again. However, looking at the drawing here http://jstookey.com/arcade/WG_25k7191/k7191-complete_lg_.jpg I notice that there are some strange jumpers it talks about (JA and JBB). I don't see how I would insert or use jumpers.

Hopefully the chip is still good, I replaced it last week. If not, it was only 3 bucks but then I have to wait for it to be shipped.

boardjunkie · « **Reply #17 on:** August 31, 2011, 10:35:51 am »

The jumpers only need to be changed if you use the 3123 in place of the 30123. If you replaced the regulator chip with the same one that came out then don't change the jumpers. That procedure is detailed on the schematic in the lower L corner.

If there's no gnd connection to the reg IC it won't regulate. Fix that first. Pin 1 should be at GND.

MajorMarco · « **Reply #18 on:** August 31, 2011, 02:45:32 pm »

I checked the circuit again, and pin 1 is connected to ground, some how I missed it when I was checking before.

Are there any other things I should check in the regulator circuit?

boardjunkie · « **Reply #19 on:** August 31, 2011, 03:03:48 pm »

Well if thats the case, and the reg IC ain't shorted, the only other thing I can think of is that the B+ isn't getting to where it should be. IIRC I repaired a 7000 once with a higher than normal B+ and no signs of life. Turned out it was a severed trace that connected the B+ to the f-back primary winding. This is in series with the h-out x-istor and the lack of load caused the B+ to be way higher. Meter the traces to that section and verify they are intact.

The traces on these boards are pretty fragile and ham fisted repairs can cause teh trace to break loose from the solder pad.

Just to clarify....you *did* replace the reg IC right? They don't need to be obviously shorted (via meter check) to not function correctly. If something's wrong in the error amp or pass sections, they won't meter shorted but once you apply power they operate as if shorted.

ed12 · « **Reply #20 on:** August 31, 2011, 08:51:01 pm »

thats a perty straight foward reg.
vdc of 145 in and 123 out

ed

MajorMarco · « **Reply #21 on:** September 01, 2011, 11:03:49 am »

145 in and 123 out? That does not seem to fit the 173 and 170.3 voltages that I received when I checked previously.

This is strange... I'll have to look at it again later today after work.

To boardjunkie: Yes, I did replace the regulator IC already. I replaced it first when the screen went blank, but when I replaced it though (2-3 weeks ago), it still did not work. I don't think I'm ham fisted, but it takes a bit of work to get the board accessable from the cabinet to test it.

Kevin Mullins · « **Reply #22 on:** September 01, 2011, 02:15:27 pm »

Quote from: MajorMarco on September 01, 2011, 11:03:49 am

145 in and 123 out? That does not seem to fit the 173 and 170.3 voltages that I received when I checked previously.

This is strange... I'll have to look at it again later today after work.

Exactly..... You need to figure out why the input voltage is so high. Output voltage is reletive to input voltage. Remove the regulator and measure the input voltage. Measure the resistance of r301. Backtrack through the power supply section.

MajorMarco · « **Reply #23 on:** September 05, 2011, 01:21:49 am »

I thought I would note that a friend of mine and I are going to look at the cause for the 170V on B+ later this week since we have had a lot of things come up recently.

However, I was looking at the flow chart listed at http://jstookey.com/arcade/WG_25k7191/wg-k7000.pdf and it shows the first thing to check is the filament circuit (since the filament is not lit)... So what is involved in checking the filament circuit? According to the schematic, the voltage on the connection "FIL" is 1,100 volts which exceeds my multimeters range. Otherwise, I don't know what else to check. Any thoughts?

MonMotha · « **Reply #24 on:** September 05, 2011, 02:44:59 am »

With no load, there'll be no drop across R103 and therefore it will hover pretty close to the 170DC rectified input. So, if the chassis is in shutdown, there will be minimal load on B+ and the input will creep up. With no load, the regulator may also be unable to pull B+ down to the regulation point due to the pass resistor (R301) to it might run high, too.

Have you tried the light bulb test? (Which looks like it may not be easily done on this design...grumble)

ed12 · « **Reply #25 on:** September 05, 2011, 04:04:52 pm »

hi
ok we have gone over this
1-the regulator=123vdc on it's output
2-the voltage at the "filament" will = 6.3 !vac! volt's a/c not 1100
>However, I was looking at the flow chart listed at http://jstookey.com/arcade/WG_25k7191/wg-k7000.pdf and it shows the first thing to check is the filament circuit (since the filament is not lit)... So what is involved in checking the filament circuit? According to the schematic, the voltage on the connection "FIL" is 1,100 volts which exceeds my multimeters range. Otherwise, I don't know what else to check

3-now come back to the regulator and tell us what u get on it's output pin ?
if the hot is shorted it will drag the :bypass: resistor down,to confirm remove the :hot: horz-output-transistor,with that done u will have no load on the regulater,but it should still reg to it's ouptput ratiting and no higher,u c these are a self comtained ciruit >ic-chip<...
if it is lower and or higher then the reg chip is done
if it is spot on,then look into it some-more
i have the manual for that chassic open and was waiting for u to respond

ed

boardjunkie · « **Reply #26 on:** September 05, 2011, 04:28:27 pm »

Kids....the heater in the tube runs off the flyback. That is part of the horizontal section, and if thats not running, the monitor will appear dead. First <<<you *NEED* correct b+ supply>>>. The protect kicks in at just a handful of volts above normal and nothing runs then. If the b+ is not what is specified for the particular monitor, find out why.

Now, did you verify trace continuity for the b+ lines as I suggested before? Is the horiz output transistor failed *open*? This is a rare occurance, but still could happen.

MajorMarco · « **Reply #27 on:** September 07, 2011, 11:42:02 pm »

This monitor is driving me nuts!

Here is what we found, from our investigation...

We have 0.6 VAC on the filament, not 6.4 VAC.

We removed IC4 and checked the input voltage and it was still 173VDC.

We removed R301 (with IC4 still removed) from the circuit and had 175VDC on the on the unregulated B+ side. I believe the regulated B+ side was 5 volts or less...

According to our diagram, only a full bridge rectifier and diodes remain, which perplexes me on how we are getting 175 volts.

We checked the 12V line and it was about 0.4 volts.

A few things to note:

The original IC4 when I got this machine was a STR30130 vice STR30123 which the diagram calls for. The machine worked great when I bought it several months ago. Regulated B+ on the diagram however says it is suppose to be 130VDC.

Strangely, the jumpers were set in my board to work with the STR3123 per the note on the bottom left. We found it strange, but the machine DID work in the past in this configuration.

Current plan:

We are currently stumped, the next thing we are thinking off is to try a variac, or build and put an attenuation circuit ahead of the full wave bridge to see if we can decrease the B+ voltage to 130+.

If anyone has an idea of where we are getting 175 volts from a full wave rectifier, I'd love to hear it!

boardjunkie · « **Reply #28 on:** September 08, 2011, 07:39:48 am »

Right....the 12v runs off the flyback as well. So it the H section ain't running, the 12v won't be there.

Correct B+ first, everything else later.

ed12 · « **Reply #29 on:** September 08, 2011, 10:59:06 am »

i think u are still missing the point of the regulater

on the input bridge and filter :no-load:,should be roughly 170vdc
u have to understand 120.vac x >rms 1.414 < would equal 145 vdc give or take a volt or so,
now what u would expect to the input of the reg. would b the full no load of the bridge,it is the output of that circuit we want to know about,remove and load on that reg. and remesurace the vdc it cannot be above 123 or 130 which ever reg u are using..
next the 6.3ac and 12vdc are
flyback sec. voltage's,these are the least of the concern right now

ed

Kevin Mullins · « **Reply #30 on:** September 08, 2011, 02:23:21 pm »

Quote from: MajorMarco on September 07, 2011, 11:42:02 pm

The original IC4 when I got this machine was a STR30130 vice STR30123 which the diagram calls for. The machine worked great when I bought it several months ago. Regulated B+ on the diagram however says it is suppose to be 130VDC.

The 130 is for 25" monitors, the 123 is for 19" monitors.
It appears they just didn't update that on the schematics.
Your regulated B+ should indeed be 130vdc.....with about 145vdc input on pin one of the regulator. (if it were a 19" your regulated B+ would be 123vdc)

Double check those jumpers though since you brought them up.....they should only be changed if going from a STR3130 to an STR30130. (different package/pinout regulators)

MajorMarco · « **Reply #31 on:** October 11, 2011, 02:53:17 pm »

I thought I'd let everyone know that I finally got it working (Actually, I didn't fix it at all, it was the TV repair shop in town that has loads of experience with Wells Gardner monitors). He said the horizontal circuit went out which included two transistors and one resistor. The voltage regulation circuit was fine.

However, now the screen doesn't adjust all the way to the bottom of the screen using the V-position pot. I'd say it's about an inch above the bottom of the screen, still playable, but a little annoying to have the black space. Any thoughts on what would cause this, or how to fix it?

sonnydaze · « **Reply #32 on:** October 11, 2011, 08:26:52 pm »

Quote from: MajorMarco on October 11, 2011, 02:53:17 pm

I thought I'd let everyone know that I finally got it working (Actually, I didn't fix it at all, it was the TV repair shop in town that has loads of experience with Wells Gardner monitors). He said the horizontal circuit went out which included two transistors and one resistor. The voltage regulation circuit was fine.

However, now the screen doesn't adjust all the way to the bottom of the screen using the V-position pot. I'd say it's about an inch above the bottom of the screen, still playable, but a little annoying to have the black space. Any thoughts on what would cause this, or how to fix it?

im fighting a 25k7191 to , how much did the tv shop charge because im about to scream

MajorMarco · « **Reply #33 on:** October 12, 2011, 02:40:15 pm »

Be aware that I had to call around and ask for rates and other charges.

I had to haul the whole NeoGeo (which is not an easy task) to his shop which was a couple miles away and the total repair bill was about $150.

Alternatively, another offer I had from a different repair guy was for $260 to come and look at it. If it was something easy with minor IC components he had on hand it was just $260, otherwise he would charge for the parts and a return visit (so $300 and up in this scenario).

Since I had a friend with a truck, hauling it was much cheaper.

sonnydaze · « **Reply #34 on:** October 12, 2011, 05:18:28 pm »

i called an arcade repair company and was told to bring my monitor and he would test it for free . if he could not repare it for a reasonable amount he had a working 25k7191 he could sell me for 100 bucks with new fly back and hot


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