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Author Topic: Tatung Monitor Won't Start  (Read 4395 times)

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Titan91

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Tatung Monitor Won't Start
« on: March 15, 2013, 08:45:51 am »
I have a 13" Tatung VS14428 type 66 monitor from a MegaTouch XL. The only thing is does it turn on the degauss coil for a second and that's it. There is no neck glow, no ringing from the flyback. Nothing else is getting power. I have checked the HOT, fuses, other transistors, diodes, and resistors in the power section of the chassis board. The primary winding in thr flyback isnt shorted either. I believe the caps have not been replaced though. I have read that old caps can result in HOT and flyback failures, but would they cause the monitor to not start at all, in the case of old filter caps?

By the way, I'm fairly new to monitor repair. What is the proper way to test a HOT with a multimeter? Do I probe the center leg from the leg itself or the screw attaching it to the heatsink? Because if I test through the center leg it's fine, shows a reading of around 500 for the outer legs. But if I test from the screw, which should be fine since it's connected to the lug, I get a short on both sides. Is this normal or a red flag? How do I know if the insulation between the HOT and heatsink plate is good?

Also, when I got the thing the white heater(?) wire coming off the flyback had broken off of its joint in the covered white part of the neckboard socket. Would running the monitor this way ruin something? I fixed it as soon as I noticed it was D/C'd but it doesn't seem to work any different.
« Last Edit: April 19, 2013, 11:59:57 am by Titan91 »

qrz

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Re: Tatung Monitor Won't Start
« Reply #1 on: March 15, 2013, 02:10:44 pm »
defective 'lytics abound in every piece of electronics .  some due to age, some due to product design .

most SMPS's will have a "small" value cap  as part of B+ filtering to the osc. ( typ 22-100uf )
there may be a pair or single resistor from raw B+ to this cap .
typical voltage here is <25v . absence could be open res or cap/IC shorted .
any bulged/domed/puffed ( whatever you wish to call 'em ) cap should be suspect.

"testing" an HOT with a meter will only tell if shorted or leaky .
with a TO-3P case style  the collector is the center pin  with base / emitter on outside legs

many H output xistors have an internal bias resistor ( 47 ohm typical ) connecting base/emitter as well as a damper diode ( reversed biased,  collector - to emitter + ).
that said , there should not be any leakage measurable from collector to base/emitter     except perhaps one way if has damper
bear in mind , the xistor is subjected to typical dc voltages exceeding 100v  and dc pulses ranging 900+Vpp when operating .

the wire described may well be the focus lead to the CRT .
it attaches to the CRT Socket and carries the 8Kv to 12Kv  needed by the focus grid
best to have it properly terminated at these voltages  ;)

Titan91

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Re: Tatung Monitor Won't Start
« Reply #2 on: March 16, 2013, 11:50:15 am »
Removed the HOT and flyback and tested them, they are good. Tested various resistors, diodes, and traces between the AC input and hot, those are fine. I see a small 8 legged chip in this circuit as well as a large filter cap. The interesting thing is the previous owner looks like he tried to run a seperate wire from the base lead of the HOT going somewhere else, like he was trying to establish another path to ground. There are also a couple of jumped traces going to a couple small caps he may have replaced. So if the HOT and flyback are both good that means the HOT is not getting power? We've spent about 3 or 4 hours trying to figure this out and we're getting nowhere... went through schematics etc. No bulging caps but all caps are original because they have the factory glue on them. The large filter cap is not in the cap kit we ordered, it only has 21 caps and there are more caps on the chassis board. We don't have a true ESR meter and can't afford one. I simply do a resistance test across a cap to verify it's not open. Any other ideas? Schematics are below.

http://newlifegames.net/nlg/index.php?PHPSESSID=cf08c9ad62f264514d99a94b4c67da40&action=dlattach;topic=1414.0;attach=16859

qrz

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Re: Tatung Monitor Won't Start
« Reply #3 on: March 16, 2013, 01:52:56 pm »
i hadn't yet taken the time to locate a print . so TNX for the link.

no pwr

check R102 / 22k  the IC B+ source (15-25v typical) with C106 as filter.
C109 is not as critical as C106. but, also important ...
the value of R114 in the snubber circuit can be somewhat critical . should be 10K - guessing 5% tolerance
MFG data on the IC :
http://pdf1.alldatasheet.com/datasheet-pdf/view/45812/SIEMENS/TDA4605-2.html   (20pgs)

has pwr, no hv
check R828 100ohm/1w on 24v source
check IC701 pin 10  for 12v  . missing , check IC101, D107

'litics around IC701 will affect h/v deflection

Hot base should connect to driver xformer via D680/R631.........

advise what values u find ..........

ed12

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Re: Tatung Monitor Won't Start
« Reply #4 on: March 16, 2013, 09:49:57 pm »
hi
if u want to print these blow them up to 200%

ed
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Titan91

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Re: Tatung Monitor Won't Start
« Reply #5 on: March 18, 2013, 04:44:45 pm »
Ed, those schematics don't appear to match the chassis I have. Are you sure about them?

Titan91

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Re: Tatung Monitor Won't Start
« Reply #6 on: March 29, 2013, 12:16:55 pm »
R102 and R114 check out. I'm going to test some other things around the power supply area. If a cap is leaky would it cause absolutely nothing to happen? Or would I see some form of activity for a split second before the watchdog circuit shuts down due to incorrect voltages? I don't have an ESR meter to test caps and we're not getting one. I do have a cap kit for this board but it seems to be missing various filter caps in the power supply section. 

Titan91

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Re: Tatung Monitor Won't Start
« Reply #7 on: March 29, 2013, 12:40:42 pm »
The transformer at T101 appears to be bad. I've tested all possible pairs on both sides and I either get open or short, no normal high resistance readings. Also no connections across the core so there don't appear to be any windings going across. However, some of these pins are shared on the primary side anyway and I'm not sure if I'm drawing the correct conclusion because I can't find anything about this part on the Internet. It's a T60001AA LTE.

Titan91

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Re: Tatung Monitor Won't Start
« Reply #8 on: March 30, 2013, 10:59:33 am »
The board also has some jumpers run, probably from previous troubleshooting. Are these jumps correct?

ed12

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Re: Tatung Monitor Won't Start
« Reply #9 on: March 30, 2013, 11:45:07 am »
jumper's on a monitor board are not un-common
as mfg's will tailor there board's to suite a coustmers need's
and or do mod's to remove part's

second u cannot propley test a transformer without a :ring: tester
and knowing what impedace and inductance to expect
with a ohm reading u are olny going by a gut feeling,and or an open
or a dead short from primary to secondary
but in line windings such as pin 1 to 4 let's say should read as a common
and a low ohm's

ed
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Titan91

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Re: Tatung Monitor Won't Start
« Reply #10 on: April 19, 2013, 12:07:12 pm »
Ok so I dropped the components I pulled back in. Would it be ok to power up the chassis board without anything connected to the picture tube? IE neckboard, yokes, etc? This would make it possible for me to live test the power supply circuit for voltage. I figure yes since nothing is getting power anyway?

ed12

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Re: Tatung Monitor Won't Start
« Reply #11 on: April 19, 2013, 07:33:42 pm »
nope

power runs through the yoke >load<
neckboard as a rule carries the picture tube ground
back down to the chassic
hook it all the way up as pre normal

ed
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Titan91

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Re: Tatung Monitor Won't Start
« Reply #13 on: April 29, 2013, 12:54:03 pm »
Thanks for the guide Ken. I have a cap kit but it doesn't cover the main filter caps/neckboard caps so I'll probably be ordering those as part of my troubleshooting because they all need to be changed anyway.

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Re: Tatung Monitor Won't Start
« Reply #14 on: May 04, 2013, 05:25:31 am »
I am working on this very same monitor right now.  It appeared dead.  No attempt at a picture when powered on.  No noises.  No neck glow.  Installed cap kit even though most of the caps I removed were still good. I have tested voltages and am seeing 93.1vdc on the neck board accross C924 so I know the power supply is working.  The HOT is warming the plate it is connected to and appears to be working.  I am inclined to think that it is a bad flyback.  I think everything is working but the HV from the flyback.

Titan91

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Re: Tatung Monitor Won't Start
« Reply #15 on: May 10, 2013, 11:59:08 am »
Interesting, I'll test it live then and check for voltage there. Moving away from the chassis I started checking the yoke windings. Horizontal is 1.1ohm and vertical is 3.5. Isn't that a little low? Also, the chassis board isn't grounded. There is no ground tab on the output side of the EMI filter so looks like it was changed. Would no ground cause the monitor to not start?

Titan91

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Re: Tatung Monitor Won't Start
« Reply #16 on: May 10, 2013, 06:21:58 pm »
« Last Edit: May 10, 2013, 07:43:32 pm by Titan91 »

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Re: Tatung Monitor Won't Start
« Reply #17 on: January 09, 2020, 02:17:03 pm »
hi
if u want to print these blow them up to 200%

ed

Hi ed... do you hapen to know where i can find the schematics for a TATUNG VT19726Z out of megatouch force 19"?

thanks