U2000 Help Please

[robsinfl]

I have a wells gardner 25k2193 u2000 monitor with a black screen. I need to know if anyone can assist me in fixing it. I dont have a manual only a schematic. Also the chassis p717 has been repaired before .... before I got it .. and there are lots of nasty solder points. Is there another chassis I could replace it with that would work with the tube and yoke I have.


Thanks
Rob

[SirPeale]

Well...you've done a good job on telling us which monitor you have.

Have you dug any more into this chassis?  Is the fuse blown, for example?  If not, does the neck glow when the monitor is powered up?

[robsinfl]

Thank you. No neck glow and the fuse is good. How do you test the flyback? I have been told this is a common failure of these models.

Rob

[SirPeale]

Check the chassis for bad solder joints and correct as necessary.

Check your B+.  Is it around 130VDC?

Visually inspect the flyback.  There may be cracking or even a hole in it.  But at this moment I'm kind of doubting it.

[robsinfl]

There is 250VDC at B+ tp202 and  0 VDC at B+ tp203. There are no visible cracks or holes. I noticed that a cooper coil part at L701 has the magnet loose and half out I dont know what this part is but would it affect the monitor. It looks like the glue has broken loose on it. Can I reglue it? I kind of looks like a horizontal width coil but its not. It has a part number of 9a2813-015 on it.

Thanks for the help.
Rob

[SirPeale]

You have horizontal deflection failure.  Measure the voltage on the collector of Q704.  If it's the same as your B+ @ TP202, check the voltage on pin 10 of U701.  It should be ~9VDC.

[robsinfl]

Q704 Measures the same 250 - 260 vdc and pin 10 / u701 measures .06 vdc

[sarge]

If your problem is the monitor won't start up, the first thing you should do is see if your monitors power supply is operating.  Does it make a clicking noise?  Lift jumper W159 and try wiring a 40W light bulb between the end of the jumper and ground to see if the bulb lights. If it does light then measure your B+, should be around 130VDC.  If your light bulb is lit and your voltage is correct, there are a couple of possibilities for the problem.  If it does not light then your power supply is not operating.  One thing to try is replacing C117 if this is the case.

[SirPeale]

Q704 Measures the same 250 - 260 vdc and pin 10 / u701 measures .06 vdc

Test Q708, Z705 and/or Z702.

[robsinfl]

Q708 has only .08 vdc on one leg, Z705 has .01 vdc on the cathode side and Z702 has .08 vdc on the cathode side.

[SirPeale]

You don't want to measure the voltage, you want to test the parts themselves.

[robsinfl]

Ok sorry. I think I understand how to test diodes check continuity both ways. z702 measures 800 ohms in ones direction and 1500 ohms the other ... z705 measures 1300 ohms one way and 85k ohms the other. The transistor as I understand it is basically 2 back to back diodes. I measured from the center pin to each outer and reversed them and got on one leg to center 1200k one way and 933 the other and the other leg to center I got 1000k one way and 0 the other.Let me know if I did this correctly and if not please tell me how.

Thanks much for your help.

[SirPeale]

Does your meter have a diode test?  Use that instead.

edit: you'll probably have to remove the parts from circuit to get an accurate reading.

[robsinfl]

All test good using the diode tester on my otc meter. I removed the transistor and lifted one end of the diodes.  I looked up the datasheet on the transistor and was wrong earlier the base on q708 was the 3rd leg not the center.

[robsinfl]

Peale all three test good what do you think ... any suggestions as to what to do next?

 

[SirPeale]

I was using Randy Fromm's flowchart to diagnose.  Until you said those three parts were okay, it was textbook.

It has been suggested to check/replace C119.  Try that.

[robsinfl]

Ok I went back and checked q704 and it is bad. I was wrong earlier. I had the collector and the base mixed up. Also r760 and r104 are bad. Any suggestions before I order these parts. Also does anyone know where to get r104 its a 10k 7w resistor in a ceramic block with standoffs and I cant find it anywhere except happs for $28.00 wich is rediculous. Mouser had it at one time but its listed as obsolete. I am trying to fix this thing as cheap as possible and then sell it.

[SirPeale]

You're sure it's bad?  Reading open?

[robsinfl]

When I test it I test from the base to the emitter and switch the leads and then do the same from the base to the collector. Using the diode test function on my meter. After doing so the base to emitter test fine but the base to the collector shows .470 ohms one way and .01 ohms the other instead of 0.L ... A transistor is like 2 diodes right and should show 0.L one way right?

[SirPeale]

Sorry, I should have been more specific.  I was talking about the $28 resistor.

Did you test that transistor out of circuit?

You're correct that you should be able to read from .400-.700V one way, but not the other.  And yes, that's volts, not ohms.  It's called a voltage drop.  It's the amount of voltage needed to get the diode to "open the floodgates" and allow electrons to pass through.  Such a small amount (.01?) is odd.  If you have a known good replacement, meter it the same way and see if it does the same thing.

[robsinfl]

The resistor test open and I tested the transitor with the diode test function on my meter I do not know what exactly that tests voltages or ohms. I have a similar transistor I can check.

[SirPeale]

Weird that particular resistor going bad.

Diode test passes voltage from one probe to the other.  It then measures how much voltage was lost on the way thru the part, and displays that amount.  This is called the voltage drop.

Yes, test that transistor.

[Ken Layton]

The U-2000 is a standard resolution monitor that does not need an isolation transformer. If you can't repair it, you could use a Wei-ya model 825H or 826H universal replacement chassis from Alva Amusement in Florida.

The Wei-ya 825H and 826H require the use of an isolation transformer though. So, if your cabinet does not have one, then you'd need to install one.

[robsinfl]

Thanks for the info Ken but I am not ready to give up on this yet.

I replaced the HOT and r104 I bought a bunch of junk u2000 and u5000 chassis off ebay for 10 bucks shipped and got the parts from them They tested good.

First I replaced the resistor at r104 and it started clicking then I replaced the HOT and the clicking stopped but I now have a b+ voltage of 160v.

Earlier I said r760 tested bad but I dont think it is. It measures 100 ohms but the schematic I have for the u2000 says it should be 470 ohms but the parts reference in the same manual says it should be 100 ohms and the other u2000 chassis I got r760 measured 100 ohms.

 I checked d106a d106b d106c and they are all good. Pin 10 on u701 is 0 volts and Q708, Z705, Z702 all test good.

Any ideas what to check next? The neck board has had a lot of repairs done to it some where down the line and is nasty looking. I checked the resistors and transistors on the neck board .. all good.  Somewhere I heard something about u701 maybe being bad?

Rob

[SirPeale]

Earlier I said r760 tested bad but I dont think it is. It measures 100 ohms but the schematic I have for the u2000 says it should be 470 ohms but the parts reference in the same manual says it should be 100 ohms and the other u2000 chassis I got r760 measured 100 ohms.

What does the color code tell you the resistor is?

[robsinfl]

It is a 100 ohm resistor.

[SirPeale]

If the color code tells you it's a 100 ohm resistor, and the reading tells you it's a 100 ohm resistor, it's not a bad resistor . 

Of course, if the schematics tell you another resistor altogether is supposed to be there, that's another ball of wax.

[robsinfl]

Right I was confused because the schematic said different. So any suggestions as to what to test next or replace as I have other boards to pull parts from? Has anyone used a company in california called pnl I heard about them on another forum. I called them and they quoted me $45.00 flat fee including shipping to repair the board I would like to do it myself but I might have to use a option like this.


Rob

[SirPeale]

So much work has been done on this, bring us up to speed about the current conditions/symptoms of the chassis.

[robsinfl]

Ok I get a black screen nothing else. The B+ voltage is 160v dc I am assuming that the high voltage shutdown is not letting the monitor work but I am not a tech. Thats about it. I have replaced the HOT and r104

[SirPeale]

Have you tried turning the B+ down?

[robsinfl]

Yes the B+ adjustment pot does not seem to affect it at all and I checked the pot and its good. Measures 0 - 1k ohms

[robsinfl]

I think I figured it out I never thought to check this but the remote adjustment board has 2 pots that have broken connections. I need to get 2 5k pots and repair it.

[robsinfl]

Wasnt that ..... I replaced the pots and it did not change.

[grantspain]

did the original hot read faulty?

[castlesteve]

I have to repair a U2000 this weekend.  So ill check back with what I have to replace to have you check as well.

Previously,  I have had to replace a couple caps on the power supply side that shorted strangely.  These are not caps that come with the standard U2000 cap kit... so I would measure EVERY cap on the power supply side (ohm meter) installed in the circuit.  If you see less than 0.5 ohm, then refer to the schematic and investigate.  Most of the time, it is a 5 cent part that goes bad (and end up paying $2 for it at a local electronics parts store).


-s

[robsinfl]

Well I replaced u101, q101, c105, c117 and t101 checked r102 and r103 (good) and now the B+ voltage is 150v so I must be headed in the right direction. Frustrating.

[robsinfl]

Swapped a few caps on the power supply side and tested every diode and resistor in that area and now the b+ is 139v

I read in randy fromms flow chart for a different wells monitor he recommends bypassing the high voltage shutdown and turning the monitor on to see if it is a horizontal deflection problem or a VOLTAGE REGULATOR problem. I said power supply problem by mistake earlier. Does any one know how to disable the high voltage shutdown and does this sound reasonable?

Also when I replaced q101 it was from a used parts chassis can someone tell me how to test a mosfet with a DVOM?

How did you come out with your u2000 castlesteve?

[robsinfl]

Ok  update  ...!!!! I replaced a bad resisitor .... I now have 130 vdc b+ voltage. I can adjust it either way as well. I still have no picture I have no neck glow and have tried adjusting the flyback and screen controls. Any suggestions? I am wondering if the flyback is bad. I have a couple I could try but they are from u5000 boards and I dont know if they are compatible.

[robsinfl]

Ok I checked and there is no voltage on pin 10 at the tube or on the board. I also ohmed the heater ... pins 9 and 10 on the tube ... and its measured 5 ohms. I also checked r812 and r823 and there good. I had a spare flyback with the same part number and tried swapping them no difference but it was off a bad chassis so it might not be any good.  I am at a dead end and need some help.