GO5-802 Issues

[ToplessZ]

Ive got a GO5-802 in an Asteriods machine.  The machine is playing blind right now.  The guy I go the cab from told the same ol story "It was working fnie, but then the pciture started to slowly fade away".    Starting off, there is no neck glow, but there is a small LED lighted on the right hand side PCB(not sure what to call it) .

I ordered a repair kit from Bob Roberts.  Installed all the caps and the 4 transitors.  NOw I have neck glow, but the red LED on the right hand side PCB isnt on??  I also noticed that the anode hole area looks funny.  I have the tube facing the outside of the garage so there is light shining around the top side of the anode hole on the tube.  It looks like someone may have tried to repaint the inside around that hole but not sure, could just be factory.  Im wondering if the anode is making a good contact?  It fits really loose even after I spead both the prongs out.

Any suggestions? 

[ToplessZ]

This is a 19" model.

[ToplessZ]

Okay, I found three fuses blown.  I replaced all of them and turned it on.  Now Im blowing Fuse F600 (2A) every time I turn it on.  The red LED is back on. 
Anyone have a flow chart for this monitor?
edit*  After reading through the manual the red LED is called a Spot Killer.  When its on, there will not be anything dispalyed.  NOw to figure out whats causing that....

[Kevin Mullins]

Down and dirty.......

Visually check for burnt resistors.

Check EVERY transistor with a meter. (including ALL the small ones)

Re-flow solder joints of course.




If you are blowing fuses then it's a sure bet that it's a sign of shorted transistors.

[ToplessZ]

Yea Kevin, your right... 
I managed to swap two of the transistors around when I installed them.  One if them is shorted now.  The other seems fine, but Ill replace it too.  Problem is I dont have any to replace then with.  Looks like a made a 15 dollar mistake, so far...bummer...
Mouser order should get me back on track..  unless you have a 2n3792 laying around?

[Kevin Mullins]

You may want to double check all the transistors before making an order of any kind.
The matching pairs on the heatsinks can be hard to come by. (the medium sized ones like the MSU 057 and such)
I believe I had to get an alternative for one of those before because they are becoming obsolete, etc.

Just better to check it all out real good first....... especially resistors as well. I forget which ones off hand, but an open resistor can take out several transistors at once.


Oh and by the way........

[ToplessZ]

Man, Ill drive out to Shawnee if your willing to give one up??  Are you going to be in OKC any this weekend? 

[Kevin Mullins]

Man, Ill drive out to Shawnee if your willing to give one up??  Are you going to be in OKC any this weekend? 

There's actually two of the 2N3716's and two of the 2N3792's pictured.
(two pairs, imagine that)

If you drove out here I'd have to show off my red-neck moj-poj junk I have laying around.
Seriously, if you think you can use one you're welcome to it. Just keep in mind how easy they are to blow if something else is still wrong on the chassis. And don't forget the insulators where needed.

[ToplessZ]

okay, Ive replaced the transistors and the fuses.  Now when I power it up no fuses blow and the spot killer doesnt light up, but the neck doesnt glow and there is still no picture and the game is playing blind..  I checked the transistors and fuses and they are all still good even after a number of power ups.  Ive adjusted the brightness and contrast all the way both ways to see if that was all.  It seems like the high voltage unit is bad now.  I ohmed everything on it and found one resistor R908 that is fully open.  One of the caps seems to 'act' open for a slight second but then acts normal. 

If a resistor ohms out to zero(meter beeps) out of circuit is it always bad? 
There are several places on the regulator PCB that have seemingly shorted parts, but after removing 3 of them I found they arent shorted out of circuit.  Could this mean that something is shorted or do parts sometimes work this way?

 

[qrz]

don't forget that the filament voltage is sourced externally. (p100/pin 11)
r908 is a 4.7 ohm  1/2 w


schematic here:
http://technical-department.servegame.com/monitor_schematic_diagrams/electrohome/GO5-802.pdf

qrz

[ToplessZ]

The link above doesnt work..
Could someone tell me what the value of R900 is?  Its a cement resistor,, I think it says 18R on it but its too hard to read...

[ToplessZ]

Figured out the value...
Now when I turn it on, nothing at all happens...  No fuses blow..no spot killer light.. no neck glow..no transistors blow...

There is a loud snap when I first turn it on coming from the transformer assembley at the bottom of the cab, is that normal?  Ive read up on the "Big Blue" cap. do you think this might be my problem>?

[ToplessZ]

What direction does the high voltage diode go in the anode cup line?  The diagrams for the manual contradict themselves.

[Kevin Mullins]

The banded side of the diode goes towards the monitor tube.
(which is where you want the high voltage to go)

[ToplessZ]

new progress! After replacing the High Voltage diode, I now have bright dots with spider webs moving around the screen, I can also see the bullets when I fire.  Im getting close, but Im not sure what to do next.  I also replaced the big blue cap and the diodes on the power supply.  Its gotta be something on the deflection pcb, but what?  The spot killer is off, and it doesnt blow fuses or transistors..