Hantarex MTC 9000 bridge coil worn off cant adjust but picture is just too large

[sollima]

I recently bought a arcade cabinet with a Hantarex MTC 9110 chassis and a US250 PSU.

The problem is that the picture is too large. About 3 cm on each side. When I wanted to correct the problem I tried to adjust te bridge coil. It had a slot for a flat head screwdriver. When I tried to adjust the ferrite coil the top part brittled off. It is still in the coil, but I can't turn it and it is set completely upward. So adjusting the horizontal bridge coil is sadly no option anymore.

I replaced all te caps on the chassis, neckboard and PSU. I replaced the pots on the adjusmentboard RV1 to RV6, and I replaced the transistors TR15, TR16 and TR17. Hoping that it would solve the problem. I can adjust the width with RV4 (10K trimmer) but if I turn it all the way clock wise the edges of the picture are just out of the viewing area.

I started googleing and found this workaround.

The problem with using a coil for the width adjustment is that the amount of change that can be produced by the full insertion of the slug isn't very much. The range of adjustment is very small. If the width adjustment is not sufficient, the horizontal size of he picture can be changed by a quick modification of the monitor.

In virtually all monitors, there is a capacitor that provides the AC return path for the horizontal deflection coil in the yoke. It's usually easy to spot on the schematic because one side will be connected to the width coil and the other lead of the capacitor will be grounded. The value of the capacitor will generally be in the range of .33 to .53 microfarads at 200 to 400 volts. The width of the picture can be altered by changing the value of the capacitor.

A higher value will make the picture wider. A smaller capacitor will cause the width to shrink. Make sure that the replacement capacitor has a voltage rating that is at least as high as the original. Changing the value +/-20% should do the job.

It suggests to change the capacitor that is connected to the width coil and is connected to ground. Does this mean that I could replace C42 with a lower value. My problem is that C42 is connected to the coil and ground, but it is in my case a bipolar 4,7uF 50V (and not  in the range of .33 to .53 microfarads at 200 to 400V)

Is replaceing C42 an option for solving my problem (schematics for MTC9110 here)?

Does anybody know the values of the (horizontal) bridge coil of the MTC9110 so I can search for a replacement?

Does anybody know if alternative coils from other systems are an alternative?

Could replacing RV4 (10K) with a pot with a higher resistance be an alternative sollution?

Thank you in advance for all your help!

EDIT: as of post 21 I now know my chassis / monitor is a MTC9000 - changed the title

[sollima]

small update:
I desoldered the bridge-coil. Now I could see the underside of the ferrite core. It had the same slot for the srewdriver as on top (the top part was brittled off). I applied pressure with a screwdriver. Gently building up torque, making sure I did not 'spun out' when it finally came lose. The upper part in the plasic cover sleve is like molten-stuck. But when appling and gently building up the force I heard it 'snap' in the middle. I believe it was just under the sleeve it was stuck in. Now I could very gently turn the part of the ferrite that was loose. I turned it as much back into the coil as I could. There is now more ferrite in the coil than when I started.

I believe that it contributed somewhat in reducing the width. But because there is less ferrite than normal the width is still too large.

I started replacing capacitors with lower capacity. But I still have not found the right one.

Hopefully, mentioning the underside of the coil will help someone with the same problem I am having.


My questions sadly remain:

Does anybody know the values of the (horizontal) bridge coil of the MTC9110 so I can search for a replacement?

Does anybody know if alternative coils from other systems are an alternative?

Could replacing RV4 (10K) with a pot with a higher resistance be an alternative sollution?

Thank you in advance for all your help!

[Ken Layton]

I've never heard the term "bridge coil".

[princess prin prin]

I've never heard the term "bridge coil".

My goodness...aren't you supposed to be a monitor expert?

[sollima]

Hi Ken Layton,

Thank you for reading my post. I've posted a picture of (what Hantarex calls) the (horizontal) bridge coil (on my chassis red part with worn out screwdriver slot on the right, and place in the manual). Partnumber 28021210 Bridge Coil UTF49.

I have been experimenting with replacing capacitors. I just replaced C41 (0.012 uF 1000V) with a WIMA MKP 10nF 1000V and then with a WIMA MKP 6n8nF 1000V. To my surprise the width was expanding instead of shrinking. The manual states that C41 should be 8n2 630V, so I think my width problem is something that was adressed in the past. (Although more capacitors were not exactly as mentioned in the manual).

So I want to try and replace C41 with a 15nF 1000V capacitor. But still hoping for the more elegant solution of replacing the width coil.

Thank you in advance for your help.

[grantspain]

is there an extra poly cap soldered underneath the chassis?

[Ken Layton]

I've never heard the term "bridge coil".

My goodness...aren't you supposed to be a monitor expert?

I've never seen a schematic for a MTC9110. I've never seen that term used before. Must be a European term. I have a horrible time trying to read European schematics. I generally don't work on Hantarex monitors and I definitely will not touch a Nanao monitor anymore.

[buttersoft]

Most of the time the horizontal coils like those don't do very much. It's a coil, so it's either conducting or burned out in some way.

[baritonomarchetto]

Just to state the obvious: check your B+ and damper diode. Have you ever seen that monitor working? Changing caps is not the best approach being that you can introduce issues, especially by toying with "sensible" components like the return cap.

[sollima]

is there an extra poly cap soldered underneath the chassis?

Thank for your answer. No capacitors of any kind are soldered underneath the chassis.


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[sollima]

Just to state the obvious: check your B+ and damper diode. Have you ever seen that monitor working? Changing caps is not the best approach being that you can introduce issues, especially by toying with "sensible" components like the return cap.

Thank you for your reply.
I must say that I have not measured the B+. I hear about this but do not exactely know where to measure it. TP10?
I don’t know the location of the damper diode. (When I locate them I will measure them)

The monitor is working fine at the moment. Colours are (as I can judge) fine. Just the sides are missing about 1> cm. I maybe have the wrong assumption that if the monitor is working the B+ should be OK.

I hear you when you say that changing capacitors is not the best approach. And issues can arrise. I try not to mess things up by only swapping one capacitor at a time. Return them when nothing happened (no shrinking of picture). Maximum of 20% capacity down in relation to the one placed originally. And only a few moments (approxemately 1 to 2 minutes) than changing it back to ‘original’ (some are different from specs).
Only at C41 I found change in width. I will use special safety KP capacitors for C41, as you and the manual stated, these are “sensible” return caps. I will first try to replace it with a new cap of the same value. Maybe the cap has gone bad.

Thank you.


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[sollima]

Most of the time the horizontal coils like those don't do very much. It's a coil, so it's either conducting or burned out in some way.

I read that too a lot. I think it is still conducting because I have picture and I can shrink it with RV4 (small potentiometer on ‘settings’ board).


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[baritonomarchetto]

The damper diode is the one soldered in parallel with the horizontal output transistor (BU508A).
Even with high voltage (an image) your ps circuit can actually be out of specs which in turn can affect the image geometry and it's fine tuning ranges.

[sollima]

The damper diode is the one soldered in parallel with the horizontal output transistor (BU508A).
Even with high voltage (an image) your ps circuit can actually be out of specs which in turn can affect the image geometry and it's fine tuning ranges.

Thank you for your answer. I am measuring all my diodes at the moment. I included a picture of the diodes I measured in relation to the HOT. I did not know which one was exactely parallel but the one in green were closed in one direction but the one in red was open (both ways there was a reading). I started measuring more diodes and found that al lot of them were open. (I measured them in circuit with a multimeter in diode-setting).



I measured the B+ this was 130V.

I'm a bit worried about all the open diodes. I think I will replace them all in hope of restoring some of the adjusment functionality you mentioned.

I replaced C41 with 15nF 1000V but I got sync issues. The upper part of the screen (about 1cm) stayed distorted. When I replaced it with the 'original' 12nF 1000V the issue remained. After I replaced it with 10nF 1000V (WIMA capacitor) it stabilized.
Now I have a screenpicture as below (I have centred it, but on the left and right somewhat is missing).

[baritonomarchetto]

BY228 is the damper. Stop toying with capacitors or you will fry your chassis
Replace the open diode, then i would start by looking at the power supply.
I am a "replace all electrolitic caps first" guy, so, if it was mine...

[grantspain]

I have repaired at least 100 of these chassis, your caps should be
c36 4n7 1600v
c40 10n 1600v
c41 8n2 630v
c37 330nf 250v and normally this has a 33nf 1000v in parallel soldered under the chassis

I would say I think your chassis may have been converted as you are missing the fan/impedance matching assembly that bolts over the flyback.
There are quite a few other components that will be different.

In my opinion I would consider replacing the chassis with a polo as I would consider this setup likely to fail badly at some point

just to clear, this is a 25" or 28" tube you have in the cab- all mtc9110 are 25-28" chassis
If your tube is 14-20" then the correct chassis is mtc9000, yours looks to be first revision mtc9000

[sollima]

BY228 is the damper. Stop toying with capacitors or you will fry your chassis
Replace the open diode, then i would start by looking at the power supply.
I am a "replace all electrolitic caps first" guy, so, if it was mine...

Ah OK. I will stop tampering with the capacitors, I do not want to fry my chassis. I will replace all the open diodes. The one you mentioned is still good. I have allready replaced every single cap on the chassis and the PSU. The voltages that my PSU delivers are all near the specified values.

[baritonomarchetto]

What grantspain said: an MTC9000 chassis in a 25-28" tube would justify the reduced horizontal amplitude, yes. Could you post a pic of your chassis/tube?

[sollima]

Thank you both for your reply.

Here is a picture of my chassis. And I measured the tube it's 20". I looked at the manual of MTC9000 and it fully corresponds with my capacitors. Even the mentioned capacitor underneath the board in the MTC9110 is absent in the manual of the MTC9000.



Picture of my chassis:




Although the picture looks very much like the MTC9000 just underneath the linear-coil there is a cilinder like capacitor that I don't have. Could this be I have a different version of the same  chassis?

[sollima]

In addition my monitor has a sticker which says: Videocolor A51-427X

[grantspain]

now we actually know what you have
so I think I saw somewhere earlier you mention one of the east/west diodes was open circuit, that will cause a similar issue- D12 and D13
C42 and TR17 are known issues in horizontal size faults on these
b+ should be 130vdc and should be checked meter ground to heatshield and meter positive to one of the centre two pins of the deflection coil connector

[grantspain]

important to note c42 should be a 4.7uf 50v non polarised cap, i use poly caps in place of these

[sollima]

now we actually know what you have
so I think I saw somewhere earlier you mention one of the east/west diodes was open circuit, that will cause a similar issue- D12 and D13
C42 and TR17 are known issues in horizontal size faults on these
b+ should be 130vdc and should be checked meter ground to heatshield and meter positive to one of the centre two pins of the deflection coil connector

I'm sorry for the misunderstanding. I was genuinely under the impression that my monitor was a MTC9110. Thank you for clearing that up.

- The east west diodes (D12/D13)  (big ones with protection around the feet and high up) were fine when measured in circuit. They measured in only one direction. D28 was open (as were more when I did a quick scan).
- I already replaced TR17 with a BDX53C (they quy form the electronic-component-store told me it would not be a problem if it was not the A version)
- I replaced all the caps on chassis and PSU. I used a biploar 4.7uF 50V. I hope that is the non-polarised cap you mentioned in the last post.

Measuring the B+ I did from the TP10 point on the board. I found it in the manual as the point to measure monitor supply voltage. But I will do it the way you suggest. I will try to locate one of the two centerpins. I presume it is the row of 4 contacts on the neck of the tube between the copper wiring.

I appreciate you taking the time to help me with my problem. As soon as I measured it again I will let you know.

[grantspain]

ok everything you have done so far is ok
the wire bridge in the centre 2 pins of the chassis side yoke connector to read b+ but you can just about read it anywhere along that line

I will look at what d28 does later when I have time

[princess prin prin]

The black and white picture is the MZ04 chassis, the very first version of the MTC9000 (14-20"). Yours is the second version, the MZ07 chassis and lastly came the BZ (01, 02 etc.). The MTC9110 (25-28") was made using the BZ chassis so it was clear from the outset that yours couldn't possibly be a 9110.

Diodes can't be measured in circuit or you get false readings (note for instance the resistor in parallel with D28) and hence wrong conclusions. You need to at least pull one leg off the chassis. The horizontal signal goes through D28 so if it were bad there would be no deflection at all.

[sollima]

The black and white picture is the MZ04 chassis, the very first version of the MTC9000 (14-20"). Yours is the second version, the MZ07 chassis and lastly came the BZ (01, 02 etc.). The MTC9110 (25-28") was made using the BZ chassis so it was clear from the outset that yours couldn't possibly be a 9110.

Diodes can't be measured in circuit or you get false readings (note for instance the resistor in parallel with D28) and hence wrong conclusions. You need to at least pull one leg off the chassis. The horizontal signal goes through D28 so if it were bad there would be no deflection at all.

Thank you for your explanation. It's my first project with an arcade monitor and I made a mistake.
Thank you for your tips on measuring diodes. I will pull one leg off the chassis when I start measuring.

Is it true that when I do get a 'good' reading (one way measurement other way OL) it can be a false reading, of are those probably correct and I should do a second reading (detached from the chassis) when I encounter a reading with both ways measurement.
I ask because I am worried that with desoldering and resoldering something could go wrong. They have small solderpoints and I don't want to accidentaly make wrong connections when resoldering. That is why I want to limit the soldering to the necessities.

But if there is no other way to get reliable readings, so be it. Replacing broken diodes is the step to take at the moment to hopefully solve my width problem.

[sollima]

ok everything you have done so far is ok
the wire bridge in the centre 2 pins of the chassis side yoke connector to read b+ but you can just about read it anywhere along that line

I will look at what d28 does later when I have time

I tried to find the spot you described, but I think I did something wrong, because my meter gives 15,43V. I attached a picture.

[baritonomarchetto]

If the diode acts as expected, the in circuit measure can be assumed to be good. If open both ways you should desolder a leg and take a second reading.

[grantspain]

ok everything you have done so far is ok
the wire bridge in the centre 2 pins of the chassis side yoke connector to read b+ but you can just about read it anywhere along that line

I will look at what d28 does later when I have time

I tried to find the spot you described, but I think I did something wrong, because my meter gives 15,43V. I attached a picture.

I said centre two pins of deflection coil header connector- look at the chassis connector

[grantspain]

d28 is on the horizontal drive, if that was open then I could not see that circuit could have been running and therefore you would not even get a picture

[sollima]

d28 is on the horizontal drive, if that was open then I could not see that circuit could have been running and therefore you would not even get a picture

Thank you for looking that up . I guess that my in circuit reading was wrong. Every time I encounter a possible broken diode I will desolder one leg to verify.


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[sollima]

ok everything you have done so far is ok
the wire bridge in the centre 2 pins of the chassis side yoke connector to read b+ but you can just about read it anywhere along that line

I will look at what d28 does later when I have time

I tried to find the spot you described, but I think I did something wrong, because my meter gives 15,43V. I attached a picture.

I said centre two pins of deflection coil header connector- look at the chassis connector

OK, i hope I have the right one this time. If not, I'm sorry, I have difficulty in identifying the deflection coil header. Googled it and I think this is it.
I think I connected to the andode-pin (see picture). Although the reading was not consistent. I've linked to a movie made of the measurement. Readings go up and down, so I probably got it wrong again. Please be patient with me. Link to movie

Thank you for your help.

[grantspain]

nope that is the crt socket
look at the main chassis, see the two green 6 pin headers behind the flyback- they are the deflection coil headers, one will be connected and on the connector you will see a link wire between 3 and 4, this is where your positive probe goes

[princess prin prin]

In this point you'll be able to attach the croc clip:

[sollima]

nope that is the crt socket
look at the main chassis, see the two green 6 pin headers behind the flyback- they are the deflection coil headers, one will be connected and on the connector you will see a link wire between 3 and 4, this is where your positive probe goes

I found it... it read 129,4V.
Any suggestions on what to pursue next?

[sollima]

In this point you'll be able to attach the croc clip:

I measured that point too, but it read 0V, strange. Though the manual states that the TP10 (+130V) should be measured one resistor to the left in the picture. I measured that one too and that was 130V.

[princess prin prin]

Those points are all the same. Probably the lead of the big resistor is a bit charred and doesn't make good contact (check the soldering and value of the resistor just to be sure). Next step, replace C42 with a capacitor like this:

http://it.farnell.com/vishay-roederstein/mkt1813547065g/condens-film-pet-4-7uf-63v-assiale/dp/1166832

[sollima]

Those points are all the same. Probably the lead of the big resistor is a bit charred and doesn't make good contact (check the soldering and value of the resistor just to be sure). Next step, replace C42 with a capacitor like this:

http://it.farnell.com/vishay-roederstein/mkt1813547065g/condens-film-pet-4-7uf-63v-assiale/dp/1166832

Thank you. I will order the capacitor through my local electronic-component store. After this weekend I hope to install the capacitor.

Is this a capacitor with the same properties or is this the wrong kind? Link to store

[princess prin prin]

It would work but it's too big and can't be installed in the proper spot. You could put it somehow on the bottom but if you can, get an axial one. Hantarex originally used a bipolar electrolytic and then switched to an axial poly cap:

[grantspain]

there was something a lot of people used to do when the width circuit had a fault, they would adjust the core of the horizontal linearity coil as a quick fix- this may be what has happened previously to your chassis