WG 7302 is dead

[kardenm]

OK guys and gals;

    I have a WG 19K7302 monitor which is dead.  No high voltage, B+ voltage is zero.  Have tested or replaced several components including;

Resistors: 802, 809(was open), 812

Transistors(Q): 402, 405, 801(was bad)

Diodes: 402, 403, 404, 801, 805(zener,was shorted)

Capictors: 326, 362, 389, 412, 422, 803, 805, 807, 808, 809, 818

Where do I go from here?
Any help would be appreciated!

[kardenm]

Surely I have'nt stumped everyone. Sure could use some suggestions!

[smartbomb2084]

Light bulb test anyone?

[grantspain]

Light bulb test anyone?

agreed but i am not 100% sure the connection points,imo desolder pins 4 and 1 on the flyback and connect bulb between 4 and ground(frame)-the b+ is marked as being 123vdc
at least that will rule out flyback
the schem i have is so blurry i can't make out where t801 is so can't be sure if thats on the vert circuit,if it is then possible there is a dead short on the vert frame ic

[smartbomb2084]

Unsolder and lift the output end of L802 in the power supply.  Connect the lightbulb between it and chassis ground. If the bulb is steady---good power supply.  If the bulb blinks ---bad power supply.  All this test does is eliminate or designate the PS as the problem.  If the bulb is steady be sure to check for +123 VDC B+ as well as the other PS voltages.

If you don't have good power you won't have a good monitor.  How simple can it be?

[kardenm]

Thanks!

GRANTSPAIN:  t801 is the transformer in the power supply section.  I would like to eliminate the flyback but not real clear how to interpert what you said. If I do the light bulb test you suggested what should I expect and, I already checked for B+ voltage at pos side of C818 and measured 0 volts.

SMARTBOMB: I will try what you suggested but probably not till Monday now. I'll let you know what I find.

[grantspain]

the test i am suggesting will rule out flyback causing the problems-you can't rule that out unless you desolder those 2 pin and check with the lightbulb(load)

[kardenm]

As an aside, I've noticed, twice now, that C803 (largest cap on board) is holding a large charge after I've removed the board from monitor.  In fact, the first time I went to test this cap it ruined a capacitance meter that I was using, second time I got a large spark when I shorted it with a screwdriver.  What does this mean?  Should'nt this cap loose its charge (thru D801 and R802 to ground) when power is shut off? Both D801 and R802 test good.

[grantspain]

the schem on wg site is too blurred for me to make out the components

[kardenm]

Light bulb test anyone?

agreed but i am not 100% sure the connection points,imo desolder pins 4 and 1 on the flyback and connect bulb between 4 and ground(frame)-the b+ is marked as being 123vdc
at least that will rule out flyback
the schem i have is so blurry i can't make out where t801 is so can't be sure if thats on the vert circuit,if it is then possible there is a dead short on the vert frame ic

Maybe this is a dumb question but how am I supposed to connect between pin 4 and ground without removing FBT?? Just removing the solder will not necessarily prevent contact with board.

Also, why is it called B+?

[kardenm]

As an aside, I've noticed, twice now, that C803 (largest cap on board) is hoeelding a large charge after I've removed the board from monitor.  In fact, the first time I went to test this cap it ruined a capacitance meter that I was using, second time I got a large spark when I shorted it with a screwdriver.  What does this mean?  Should'nt this cap loose its charge (thru D801 and R802 to ground) when power is shut off? Both D801 and R802 test good.

In general, should I always expect the large caps on a board to be charged long after power is turned off? I've not heard this mentioned before nor have I ever encountered this and I've tested alot of caps on alot of boards.

[kardenm]

Unsolder and lift the output end of L802 in the power supply.  Connect the lightbulb between it and chassis ground. If the bulb is steady---good power supply.  If the bulb blinks ---bad power supply.  All this test does is eliminate or designate the PS as the problem.  If the bulb is steady be sure to check for +123 VDC B+ as well as the other PS voltages.

If you don't have good power you won't have a good monitor.  How simple can it be?

Tried this. Bulb not light at all. ??

[smartbomb2084]

Are you sure you hooked it up right?

[kardenm]

Lifted end of L802 which is connected to C818, connected one side of 60w bulb(which I tested) to lifted end and other side to monitor frame (which has two chassis ground wires attached to it.

Also, while I was at it,I connected bulb across fuse terminals (with fuse removed). When switched on, bulb lit brightly but quickly dimmed to no glow.  Does this tell me anything?

Thanks for your advice.

[SirPeale]

Also, while I was at it,I connected bulb across fuse terminals (with fuse removed). When switched on, bulb lit brightly but quickly dimmed to no glow.  Does this tell me anything?

Quite a bit, actually.  Replace the fuse and it probably won't blow.

No glow...or very very dim glow?  Do this in low light conditions.

[kardenm]

I'll try.  Fuse had not been blown, by the way.

Are you saying to try the test again WITH the fuse removed??

[kardenm]

Tried it again.  Bulb goes completely out in about 3 seconds. (with fuse removed).

[kardenm]

Looking at schematic; I have no power at L802 but, I do have power at C803 charging it to at least 200v. So, I do have power comming out of the bridge rectifier and going to transformer T801 but no power comming out of T801 to L802.  I guess T801 could be bad or I802 or associated components. Any way to test I802 (STR-S6707)?

[SirPeale]

The bulb trick is really only necessary when the fuses keep blowing.  Since yours is not, you don't need it.  It adds a ton of additional resistance.

[smartbomb2084]

Are any pins of I802 shorted to pin 2 of I802?

[kardenm]

Are any pins of I802 shorted to pin 2 of I802?

No. None are shorted to pin 2.

[kardenm]

Still have not solved this one. Have tested or replaced many components. Problem is almost certainly in power supply section. More on all that later.

For now, when I plug this in, I hear a faint ticking sound with a freq. of about 1 per sec.  Can some one tell me what this is and why?

[MonMotha]

Still have not solved this one. Have tested or replaced many components. Problem is almost certainly in power supply section. More on all that later.

For now, when I plug this in, I hear a faint ticking sound with a freq. of about 1 per sec.  Can some one tell me what this is and why?

This is usually the power supply (SMPS) attempt to start into a heavy load (e.g. short) then giving up and attempting to restart again later, hence the repetition.  The actual ticking is generally some magnetic component physically moving just a little bit as all the fields change due to startup/shutdown cycling.  Basically, something on the output of a power supply is probably shorted or very leaky.

[kardenm]

As an aside, I've noticed, twice now, that C803 (largest cap on board) is hoeelding a large charge after I've removed the board from monitor.  In fact, the first time I went to test this cap it ruined a capacitance meter that I was using, second time I got a large spark when I shorted it with a screwdriver.  What does this mean?  Should'nt this cap loose its charge (thru D801 and R802 to ground) when power is shut off? Both D801 and R802 test good.

In general, should I always expect the large caps on a board to be charged long after power is turned off? I've not heard this mentioned before nor have I ever encountered this and I've tested alot of caps on alot of boards.

From stuff I've read (ex Monitor FAQ's) (http://forum.arcadecontrols.com/index.php?topic=45137.msg915800#msg915800) this cap should not stay charged when power is turned off. Indeed, on an identical, working board that I have , this cap does not stay charged.  The fact that this one stays charged (aprox 180v) means something else is defective. Any can shed some light on this?  

Again:

Looking at schematic; I have no power at L802 but, I do have power at C803 charging it to at least 180v. So, I do have power comming out of the bridge rectifier and going to transformer T801 but no power comming out of T801 to L802.  I guess T801 could be bad or I802 or associated components. Any way to test I802 (STR-S6707)?

T801 and I802 are not the problem as I replaced with good ones from the working board.  Could the bridge rectifer (D801) test good but malfunction when power applied?

[kardenm]

Anyone??

[lilshawn]

The fact that this one stays charged (aprox 180v) means something else is defective

all that means is that there is something that is open on the high voltage circuit, something that would normally "bleed" off (use up) the voltage in the circuit and drain off the cap.

start at the cap and start working your way across the components... eventually you will find something wrong. It's just a matter of elimination...

[kardenm]

But I have no voltage comming out of T801 (measured at C818 for ex., ie. no B+ voltage).

[kardenm]

I've had a small success!!  I replaced the bridge rectifier (D801) which had tested good when out of the circuit but did not seem to be doing what it was supposed to do. Now I have some measureable B+ voltage. I'm getting 65.5v. Supposed to be 123v.

Can anyone tell me where to go from here?? (still no high voltage and no picture). Also still hear tick, tick.

[SirPeale]

Sounds like its in shutdown.

[smartbomb2084]

Try the lightbulb test again.

[kardenm]

Thanks. I'll try that again soon as I get a few spare minutes.

Tried light bulb test again.  Bulb not light at all. Still hear tick tick.

[kardenm]

From other post.

lilshawn.   Still beating my head against that wall.  Still seems to be a power supply problem.  I802 (STR-S6707) was bad (not the bridge rectfyr).  I can measure an on/off voltage at L802 (B+ voltage) and can hear a ticking of about one second freq.

Have been in touch with Wells Gardner tech support.  Had already replaced several components which he said were likely culprits such as zener diode D805, Q801, R809 (which was open), and C807.  Have replaced a few bad caps and tested almost all components in the power supply section.  Guy at Wells said to test Q802(voltage detector SE120N or NTE#7216) and the optocoupler(I802/PC123Y11). 

That's where I'm at with this.  Unfortunately I have no history on this board as I inherited it in it's present, nonworking condition.

Thanks again for your help.

[kardenm]

 

Great news people!!  I finally got this board working.  I had gotten as far as isolating the power supply section and hooking up a light bulb to the 123v output (B+).  Bulb did not light so I knew I still had a bad component in this section even though I had tested and/or replaced every pwr supply section component.  Soo.. I started over by rechecking everything.  Sure enough, found a bad transistor(Q801), replaced it, bulb lit up as expected, put everything back together, monitor fires up and I have a picture now!!!

Only problem left to solve is that the picture is to dim, cannot adjust any brighter.  Anybody have any suggestions?  I have already replaced or checked most of the electrolytic caps (but not all).

In any case I really appreciate help that was offered and I learned alot in the process.  Thanks!!

[MonMotha]

If black is not yet becoming gray ("brightness" is too low"), try tweaking the "screen" control on the flyback up a hair if you've not done so.  It's not uncommon for things to need adjustment after a shotgun cap kit since so many parts suddenly change value.  If black is already becoming gray but colors need to be brighter (you need more "contrast"), the RGB drive pots, usually located on the neckboard, often have quite a bit of adjustment range.

There's also sometimes a "sub brightness" or "sub contrast" control hidden somewhere on the board, but I don't remember if the k7000 series has these or not.

[kardenm]

Have adjusted screen control high as can without going grey and messed with RBG cntrls on neck board.  Cant get rid of dim picture.  Also there is a darker area on right side of screen (looks like smoke).  Cant find any hidden/unknown pots on the board (yet).