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GuruSantiago

TI Color Monitor problem. Looking for schematics.

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My TI color monitor just started to have a problem. The vertical linearity is way off, it seems like something overheated a few nights ago. 

 

I searched for a service manual and schematics, but I did not find one. Is there a schematic for this monitor anywhere? 

 

The Model is PHA4100A. The Chassis number is NMX-K6NC. The monitor was manufactured by Matsushita Electric Industrial Co. of Fukuoka Japan in 1983.

 

Thanks in advance.

 

GuruSantiago

 

 

 

 

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Posted (edited)

Don't have the schematics... been a while since I worked on that particular issue... if you are at all familiar with T.V. sections... Following the wires from the deflection yoke coils to their destinations can often be enough to locate the Vert. deflection section.... usually two transistors with heat sinks, driven by an I.C.. I'd probably start by checking the electrolytic capacitors near the I.C., replacing with tantalums as I go... also sometimes there is a v.lin. adjustment pot. or fixed resistor.

 

    P.S. Sorry, if I'm being presumptuous.:)

Edited by HOME AUTOMATION
punctuation
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It may be necessary to see if it's a vertical deflection IC or a simple vertical deflection circuit.  If it's an IC, it probably has integrated sawtooth generator feeding into a feedback circuit and then into the output amplifier.  The intent is to make sure the vertical deflection moves as commanded by sampling the actual output into the feedback part.  There are a few transistors, capacitors, and probably even a transformer involved.  So there are a few things to go wrong.

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If you have never worked inside a TV or CRT monitor before, I want to stress that there are voltages in there that can kill you.

 

I have found some of the best monitor troubleshooting info and help is on the arcade-museum.org forums.  The schematics for the TI monitor are probably going to be very hard to find.

 

You will probably get a lot of suggestions to do a cap-kit on the monitor, which I used to be an advocate of.  However, the last 3 monitors I did the cap-kit on, the new parts (caps, HOT, and various resistors) put too much stress on the older parts there were not replaced, and the result was a blown fly-back or killed other more obscure parts.  Even when a replacement fly-back was available, the new one would die very quickly.  It has been very frustrating because parts like the fly-back are very specific to the monitor, and finding replacements is sometimes impossible.  Trying to find a substitute would probably require an EE degree and in-depth understanding of the high-voltage section of CRTs (as well as the electrical specs on the CRT tube and coils).

 

Remember the CRT is 30 to 40 years old, and finding and replacing failed or aging components will not always fix the monitor, or keep it working for any period of time.  It is unfortunate for sure, and I don't think there are any companies remaining in the world that are actually making CRT monitors or parts for them.

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Posted (edited)

Oh yeah, not only do the mains and HV caps store juice... the screen grid in the CRT can make it act as a Leyden jar! ...get too close and, ZAP!!!:o ...I did this when I was seven.:lol:

 

I heard that when the Flyback or H OUT transistor blow repeatedly ...the high voltage clamping diode should be replaced.

 

I replaced a Sony Flyback on a large screen TV, with one from a similar model in the early 90's. The replacement part# was only off by one digit. After removing and comparing side-by-side... to the naked eye, all was the same... except for the coupling of one set of coils and the orientation of one leg. This required the cutting of two traces and cris-crossing jumper wires. After replacing a couple passive components... the screen dimentions were right. I did this "in the field" got paid $40, went home. A few days later I get a report that something's not right with the picture... they said that the letters were messed up and they couldn't read, when words were on the screen. I had a feeling what the problem might be... yes, the image was mirrored. I cut the wires to the horizontal yoke coil and reversed their connections. Problem solved ...not very profitable!:twisted: Lots of travel, time. Maybe I should have charged for the part.:grin:

Edited by HOME AUTOMATION
Hey... I didn't re-post!
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On 7/21/2019 at 10:02 PM, matthew180 said:

If you have never worked inside a TV or CRT monitor before, I want to stress that there are voltages in there that can kill you.

 

I have found some of the best monitor troubleshooting info and help is on the arcade-museum.org forums.  The schematics for the TI monitor are probably going to be very hard to find.

 

You will probably get a lot of suggestions to do a cap-kit on the monitor, which I used to be an advocate of.  However, the last 3 monitors I did the cap-kit on, the new parts (caps, HOT, and various resistors) put too much stress on the older parts there were not replaced, and the result was a blown fly-back or killed other more obscure parts.  Even when a replacement fly-back was available, the new one would die very quickly.  It has been very frustrating because parts like the fly-back are very specific to the monitor, and finding replacements is sometimes impossible.  Trying to find a substitute would probably require an EE degree and in-depth understanding of the high-voltage section of CRTs (as well as the electrical specs on the CRT tube and coils).

 

Remember the CRT is 30 to 40 years old, and finding and replacing failed or aging components will not always fix the monitor, or keep it working for any period of time.  It is unfortunate for sure, and I don't think there are any companies remaining in the world that are actually making CRT monitors or parts for them.

I agree with you 100%. Years ago, I repaired TV's and I know how parts that are degraded will fail when new and stronger componts are added.

 

My hope was to find the schematic before didding in. I already checked for a vertical linearity adjustment, but I didn't find one. The amount of dust is so much that I need to clean the monitor first before I make an attempt to a repair. I suspect that the problem is in the ramp generator for the verticle. maybe a bad resistor or cap used to linearize the ramp.

 

Thanks for your feedback. I agree on the no re-capping. Too many people latch on to that as a firs step. I have been in the industry long enough to know not to fix it it it isn'y broke.

 

GuruSantiago

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On 7/20/2019 at 6:01 PM, GDMike said:

I was just about to mention verticle sect. Spray with coolant..

It does this when it is cold, so the cool spray may not make a change. 

 

I have a friend that hit a Sony TV with some cool spray and it seemed to fix the issue, then he heard a loud pop and the TV died completely.

 

The best approach is always using a volt meeter and a scope to isolate the problem.

 

Thank You,

GuruSantiago

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I appreciate the feedback. I will continue my quest to find a schematic. If it is impossible, I will reverse engineer the vertical section and start troubleshooting  until I find the problem. I have seen and fixed this on TV's and Arcade Monitors in the past.

 

Thank You all,

 

GuruSantiago

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