Dead 9110

[marshall]

Ive just changed the capacitors on a Hantarex 9110, then connected it all back up expecting a nice crisp picture, but was greeted only with a  static crackle as if the monitor was coming on as normal but no picture.

The fan tries to start but only moves a little.

No neck glow.

No obvious bad joints, Ive done this job before with no problems!

Fuses all ok.

What next?

[marshall]

OK I admit it, Im stupid!

Ive put C57 in the wrong way around!!!!!!!!!!

Its been swapped for the old capacitor and inserted the correct way around, but still no life, what have I fried?

[grantspain]

check whatever else you did,btw caps normally explode when inserted wrong

[marshall]

It was only the capacitors I touched, when it went back in, I get the static and the fan tries to start but doesnt and the static stops. Swappes C57 for the original, but the right way around, still same symptoms, I must be jinxed, get one monitor working then fry another.
Have checked all the other caps and they are ok, only one in doubt is C38 as there is no orientation on the board, which side should the nagative be?

[grantspain]

perhaps you are barking up the wrong tree,the most common fault on the mtc9000 series was the HOT,power transistor and flyback-normally you see the big load resistor glow orange

[marshall]

Im getting 136v DC at TP 10, static build up on start which quickly stops and the fan stops trying to spin, so that rules out  C34, C53, TR20 and the X-Ray circuit, also the big resistor is not getting hot.

I have also checked ZD1 which is allowing current one way but not the other, so that hasnt shorted.

Now what?

[grantspain]

so you are getting a constant 136vdc b+?

[marshall]

Yes voltage was steady, video inputs disconnected, I'm using an old analogue meter so not sure how accurate it is!

[grantspain]

you checked tr15?collector to heat shield

[marshall]

No, which pin is collector and what should the Reading be?

[grantspain]

with the power OFF meter centre pin of tr15 to heat shield it is clipped to using continuity or ohms-should not be dead short

[marshall]

Ok have checked it and its not short, its reading about 3.4k ohms.

Have also replaced all but one original caps (C42 left) and same result, static noise fan tries to start, static noise stops as does the fan.

[lilshawn]

sounds like the startup circuit for the power supply or something with the x-ray protection.

[marshall]

I thought if it was the X-Ray circuit there wouldnt be the 130volt at TP10? Isnt there a diode which if disconnected with show if its the X-Ray or not??

How do I check the start up circuit?
What is the next thing I should check?

[lilshawn]

sorry i was thinking of another chassis this one has discreet components that make up the power supply not a chip

check c56 it appears to be the power level feedback cap. you might as well change it if you haven't already. also check r100 to see if it's gone open, it's directly upstream (powerwise) to your backwards cap. the extra load of the cap would be a great strain also on tr21 check it out.



if you put a voltmeter on the # 3 or 4 pin for the yoke "CO" connector what happens when you fire up the unit?

red to the pin and black on the chassis ground. meter set to read DC in the 200 volt range if not autoranging.

****CAUTION****there may be +130 volts present be sure to take appropriate safety measures*****************

does the voltage spike up and then drop down again? if so while still connected ,turn down the voltmeter to a lower voltage reading setting. see if there is anything there. it may be only a small (possibly less than 4 volts) oscillating power being supplied. but something is better than nothing.

[marshall]

I will change R100 and replace C56 but have no idea how to check TR21 so will change it anyway, then take a reading on the yoke. I assume you mean the connection which has 6 connections as in the picture? It has 4 wires on it, 2 yellow a red then 2 spare then a black.
It will be tomorrow before I can get the parts so will post what happens after that.

[lilshawn]

your B+ voltage (130) runs up to the yolk connector(s) and down again (i presume to cut the supply power to the rest of the board in case the connector got unplugged)

Would like to get a reading from there since it seems to be the end of the line before it gets to the rest of the chassis...

[marshall]

Im having trouble getting the transistor and looks like they will be a few days before arriving so will just take a reading on that pin anyway and get back to you.

[marshall]

Have been clearing the garage this weekend and finally got those readings for you.

On pin 3 of the yoke I get 0.5 of a volt and then as static noise stops the voltage it goes to 0, the curious thing is that its a - voltage, in other words to get a + voltage I have to have red probe to chassis and black probe to pin 3/

[lilshawn]

well sounds like you might have a bad diode in the rectification area d19,20,21,22 or a bad C53. also check TR20.

i think you are just getting a negative voltage just because of the feedback caused by collapsing magnetic fields when the power shuts down.

i'm just concerned that your meter isn't responsive enough to see the initial inrush of voltage. I cant tell if it's powering up and shutting down, or not coming up at all.

i don't want to send you off shotgunning parts off the board

[marshall]

The C53 is expensive to purchase so want to leave that till last!

The negative voltage is showing until it shuts down, then goes back to '0', its an analogue meter and quite sensitive, if there was anything there it would let me know. Im no expert but it seems like its coming on but quickly shutting down.

Is it worth changing the diodes or should I just check them?
I have no idea how to check TR20, how do I do that?

I dont mind changing every componant on the board if I have to, but would like to know where to start............

UPDATE...

Ive just unsoldered one end each out of D 19,20,21,22 and not getting continuity, is it likely they have all failed open?
If i set the meter to measure resistance on the 200M scale I get a reading, does that sound right or have they failed?
Checked R100 and its ok.

[lilshawn]

if your measuring diodes with  the resistance setting, test it one way then the other, you should have some resistance one way but not the other. if you get resistance both ways, it's shorted and needs to be replaced.

[marshall]

Its definatly only one way but a high resistance, I thought it would be straight continuity.

[lilshawn]

diodes have what is known as a "voltage drop" because of it's design, it doesn't have perfect continuity. IE if 12 volts begins to flow through one side of the diode, you would measure 11.4 volts (aprox.) because the voltage drop on most diodes is about .5 to .6 volts.


it should have "zero" or read "open circuit" in one direction and have resistance in the other (when the leads are reversed)

[marshall]

Im not getting zero resistance but a very high resistance so think they will be put on the list of parts to change.

[lilshawn]

to be quite honest, i don't even know what a diode should read when measuring it with the resistance setting, since my meter is digital and has an actual diode test function.....BRB....

okay, a good diode I have here measures 2.2 megaohms with the red lead on the unbanded side and the black on the banded side of the diode....reads "open" or infinite resistance with leads revesed.

[grantspain]

you have to remove one side of a diode when reading

[marshall]

Thanks grantspain, I did remove one side to measure it, still got the result as above.
Maplin dont stock that particular diode but do stock something which handles more power so Im hoping that will be ok?

Ive just bought an Operation Thunderbolt which is faulty but they said the monitor is ok so Im going to fetch that on Sunday and hopefully that will resolve the problem, then put the old monitor on Ebay so its someone elses problem but will have to see how it is on Sunday.