Hantarex MTC-900 Issues

[SirPeale]

Interesting reading...

"G1 normally is a negative voltage. Most tv picture tube do not use G1
voltage. If the G1 voltage is missing or zero voltage to the picture tube
the monitor display will becomes very bright with retrace lines (diagonal
lines or flyback lines) across the screen and sometimes the monitor will
goes into shutdown mode."

which sounds exactly like my problem.  Now I need to find where to measure my G1 voltage from.

[grantspain]

its nothing real daft like the dag earth disconnected from the neck card(don't bite my head off,just a suggestion)
according to the schem the 900 does not use -190v g1,it marks g1 as pin 5 which is to earth(thats of course if i am reading the correct schem)
have you checked also
r144 2.7ohm
r59 2.2kohm

[SirPeale]

its nothing real daft like the dag earth disconnected from the neck card(don't bite my head off,just a suggestion)

Nope.  And it should still fire up, even if it were disconnected, right?

according to the schem the 900 does not use -190v g1,it marks g1 as pin 5 which is to earth(thats of course if i am reading the correct schem)
have you checked also
r144 2.7ohm
r59 2.2kohm

I'll check those resistors later.  Thanks for letting me know which one was G1.

[SirPeale]

Those resistors checked out fine.

[lanman31337]

Slightly off-topic, but you guys are amazing with your work.  My father-in-law does repairs like this, and the wealth of knowledge is huge.  My hat is off to you fellas.  I'm scared to crack open televisions and monitors.

[SirPeale]

I spent the last hour going over this board, touching up solder joints and replacing the drivers in the neckboard.  I also took a cotton swab and cleaned the bottom of some kind of scum.

The good news is that it isn't driving full force anymore.  You can turn the screen control down now and it goes dark.  And you have to turn it up a decent amount to see scanlines now.  It's still a yellow tinge.

The bad news is that there *still* isn't a picture of any kind.

Something to note: the brightness and contrast controls don't seem to have any effect.  Yes, I've checked D9 and D34.  The pots themselves seem  okay.

[grantspain]

something in the video amp circuit,probably missing a voltage
are you the schem to trace things?
see i said you are nearly there

[SirPeale]

Better now than I was.

Randy Fromm's flowchart describes this problem and the parts to check.  Unfortunately there isn't a flowchart for this monitor.  I'll be curious to see what parts are affected.

[grantspain]

if you had this problem on a later chassis like a polo then one of the first things i would have suggested is replacing the lm1203 ic which is a video amp/decoder.the 900 chassis does not have this ic but a load of components doing the same job-the fault has to be common to that circuit

[SirPeale]

It's a large board, it's going to take me a while to go thru it.

[modessitt]

Well, i don't usually visit here anymore, but I may have some info that may be relevant - and may not.

I was working on a different model Hantarex (MTC9000) that was dead, and came to life with a cap kit, but couldn't for the life of me get a picture on it.  This is what I ended up with:



I also checked every damn thing i could think of and got nowhere.  I wasn't even getting flashing in the lines to indicate it was TRYING to draw the picture.

After a few weeks of scratching my head, I decided it needed a fresh set of eyes, so i took it to a buddy's house for him to look at.  He also did what you are doing - replaced the IC, changed out transistors and diodes and caps and whatnot.  Nothing worked.

Finally he just pulled out his meter and started doing continuity checks on every trace.  He finally found a trace on the neckboard that wasn't showing continuity from part to part, even though nothing looked evident to the naked eye (or under a magnifying glass for that matter).  He jumpered the trace and the picture came up just fine, and is now one of my prettiest monitors.

Just thought it may be relevant to your issue...

[SirPeale]

Well, i don't usually visit here anymore, but I may have some info that may be relevant - and may not.

Why not, mate?

[SirPeale]

I would suggest talking to Jomac in Australia about your problem. I think his new "Ultimate Monitor Repair" book at Star Tech Journal has a chapter devoted to Hantarex monitors.

I sent him an email last night.  His reply was:

If you post on www.arcadecontrols.com  I'm sure plenty there will be able to help you, I get around 40 of these requests per day so as you can imagine there isn't enough hours in a day to respond to them all , unless of course your intention was to send it to me for repair.

[SirPeale]

I have written a repair guide to the 900/E. There's a difference between the 900 and 900/E.

I'd like to get a copy, if that's okay.  My email is in my profile.

[SirPeale]

Jomac emailed me back with another reply. 

You couldn't have picked a more difficult monitor to tackle for you first effort , the color drive circuit is well over engineered to the point it can only cause problems .
A couple of things you need to establish , 1st find a ground point SP5 on neck board , measure all voltages with meter on DC , Check pin SP1 which is brightness pin , voltage should go up down as you adjust brightness , maximum 12 volts.
As this voltage drops the brigtness on the screen gets brighter , so to test of neck board itself is ok , momentarily short SP8 pin to Gnd , this will give maximum brightness .
To test all colors on CRT , you can momentarily short one end of R141 , 143 or 146 to Gnd , this will drive each color flat out one at a time and tell you if tube is ok .

Next using same ground point , measure SP10 , this is red input from chassis to neckboard , it should go up and down when you adjust RV3 red control on the chassis
Measure voltages at IC1  5 volt regulator , facing you , input on left is 12volts , Center pin is gnd , right pin is 5 volts .

[modessitt]

Well, i don't usually visit here anymore, but I may have some info that may be relevant - and may not.

Why not, mate?

I spend all my time over at the KLOV forums now.  While this is a good place to talk monitors, the arcade section isn't that lively for my tastes, and I'm not that into MAME stuff.  Since i fix the arcades for a living, it makes more sense to participate over there...

[SirPeale]

I'm still beating on this thing.  This is the first time I've touched it since my last post on the matter.

Jomac gave me some things to check.  He said to check the voltages on IC1, they should be 5 and 12V, with the middle pin as ground.  I'm not getting that at all, I'm getting 27V and 30V.  Also he said to meter SP5(gnd)  to SP8(brightness) and that should be a maximum of 12V.  I'm getting zero.

[grantspain]

there is a 12v regulator you should check

[SirPeale]

there is a 12v regulator you should check

Is that IC4?  Because I've already replaced it.  Though I suppose it could have gone bad again since I've done a lot of work since that point.

[grantspain]

yes thats ic4,the readings you are getting are off the scale
maybe worth metering back to ic4 to see whats happening

[SirPeale]

Definitely.  I'll give it shot. 

[SirPeale]

I've verified the voltage on IC4 - 12V(ish) out.  What's the input voltage supposed to be?  It's also very close to 12.

[grantspain]

the specs note 19v as input and 12-12.5 output for 7812

[SirPeale]

Five volts off input...what should I check?

[SirPeale]

Also, since I'm missing the brightness voltage, that comes right off the flyback.  Could the flyback be bad?

[grantspain]

i thought you had put a new flyback in,
check
byv95c-d27
100uf 25v-c85
0.5ohm-r116
this is gonna be an epic repair post btw

[SirPeale]

i thought you had put a new flyback in,

Nope.  If it comes to that I'll just ditch this.  Epic indeed!

[grantspain]

probably end up being cheaper to get a replacement chassis

[SirPeale]

probably end up being cheaper to get a replacement chassis

That's why I'd ditch it if it needs a flyback.  I've got a million components lying around in old TV chassis I can rape from.  Flybacks are a different matter.  I priced them for this monitor not long ago, and it was like $40 plus shipping.  Heck with that, I can get a junk game with a working monitor and use that.  If I can fix this, then good, it'll go in a game and get sold off, but at this point it's my "Everest".

[grantspain]

dunno on this,never seen a flyback lose just one winding(poss though i guess)
what voltage are you missing,190v video?

[SirPeale]

i thought you had put a new flyback in,
check
byv95c-d27
100uf 25v-c85
0.5ohm-r116
this is gonna be an epic repair post btw

D27 - good
R116 - good
C85 - near as I can tell, good.  I even just replaced it with a brand new one.  Same thing.

I seem to be missing 12V on the neckboard (brightness).  No voltage there at all metering SP5 to SP8.  That goes right back to the flyback.  I can trace from there back but so far all I've tested have been okay.

IC1 is getting way too much juice.  Should be an input of 12V and output of 5V, right?  There's an input of 30 and output of 27.

[grantspain]

yeah sorry,knew about the 12v .i thought you meant another

something skying the 12volts out,hhmmmm
d8,d6,r175(560ohm),d17
you know i never give up with a fault,i keep going-took me 3 weeks to fix a ceronix once ,kept on going back to it in my spare time-turned out to be a broken track

[SirPeale]

yeah sorry,knew about the 12v .i thought you meant another

something skying the 12volts out,hhmmmm
d8,d6,r175(560ohm),d17
you know i never give up with a fault,i keep going-took me 3 weeks to fix a ceronix once ,kept on going back to it in my spare time-turned out to be a broken track

I'll do the same.  Only reason I won't fix this is if it's the flyback.  Everything else I should be able to source from TV chassis.

[mcfreak]

If it would help you, I have two Hantarex 900E chassis's that I was trying to get working.  One had a blown flyback and the other wouldn't stop vertical rolling.  I switched the flybacks and now the other one is very dim, even if everything is turned all the way up. 

Would either of these help you in your quest to get your monitor working or be worth shipping for you?

[SirPeale]

HECK YES.  At the very least I could limit the problem to one board or the other, then concentrate specifically on that board to finalize the repair.  It's extremely frustrating, to say the least.  I know the problem is in the brightness circuit, but haven't found it yet.  Then again, I haven't touched it since my last post. 

[Ken Layton]

If you throw in the towel on this chassis, the Wei-ya model 1220H (requires isolation transformer) universal replacement chassis will work. Just $45 from Alva Amusement.

[SirPeale]

Thanks, Ken.  But half of the fun on this is figuring out exactly what's wrong with it.  If I can fix it for the cost of a few scavenged parts, fine.  If it needs something major like a flyback, I'll give it away.

[Carlito]

Hi Peale,
   Was just wondering where you got the cap kit for this particular monitor?  I checked bob roberts and only the 900/E is listed.  The monitor is working ok, but the colors are a little washed so i'm hoping a cap kit fixes it.

Thanks for any information and I hope you get yours working.

[SirPeale]

No kit.  I work on these things a lot, so I've got a bulk of caps here.

[SirPeale]

I got a MTC 900/E from mcfreak.  As he described, it comes up dim, but usable.  So I've definitely got a good tube. 

I was going to swap boards from one chassis to the other (power supply, etc) but I'm not sure just how compatible they are.  They look so very, very close.  Connection @ P23 (I think) isn't there on my 900, but is on the 900E.  As an experiment I connected the two to see if I'd get a picture (I didn't). 

I went through every resistor on the power supply looking for an open one, but didn't find any.