Electrohome GO5-802 in my asteriods

Malice95

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So I have a Electrohome GO5-802 in my asteriods. Previous
owner said monitor stopped working but game played blind
then game stopped a few weeks later. I got the game playing blind
by replacing some fuses. but I cant get the monitor going.

I checked all the fuses nada...

When I power up I notice the red spot killer led lit on the
deflection board and I have a faint dot in the middle of the
screen. I turned the brightness all the way up for a few seconds
and couldnt see any game image.

Any way to tell if the game PCB isn't sending a signal and kicking off the
spot killer or the deflection board is bad?

If we assume based on the history thats its most likely the deflection
board.. what would you suggest looking at on it?

I dont have an occiliscope.. just a digital multimeter.

Thanks,
Crayola
 
If the led is lit on the deflection board it is indicating a lack of deflection input from the pcb.
With your multi meter you can test the for voltage on the main pcb in the following ways.
+ 5v DC on pcb the led is lit. You can confirm this at the test point. You can also check the output voltage at x and y test points they should be swinging between +5 and -5 volts DC.
If they are stuck at a constant voltage you know you have a pcb problem or an issue with the A/R board. The A/R Board can be tested in the following ways. Test points (Sense) should be +5 volt and the unregulated voltage should be around 14 volts.
 
So i did the tests you mentioned.. the X and Y sense points show a rapid
up a down activity.. all less then +5 to -5 that I could see.

I checked the 5v and 10.3 v test points on the AR board and they came back
as 5.38 and 11.4. If I adjust the voltage down.. I'll be to low on the 5v part.

I noticed a bad diode that burnt up on the AR board. (this isnt my board picture
btw.. just a reference for which diode it was). Not sure of its purpose but its passing
current both ways. The traces on the back it is attached to are still showng continuity
around it.

Where do I go next?

Thanks,
Crayola
 

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Of course I will replace it... but given there is output at the X and Y
and the test points show the correct voltage..I'm thinking its something else?

Thoughts?

Malice95
 
Correct. The A/R board can be shot gunned to remove R29 and R30 from the equation in the following manner. On connector J7 on the solder side connect pins 1and2 Next connect pins 3and6 they should be marked on the front side of the board. By doing this you remove the ability of the board to increase power to the pcb because it is designed to sense low voltage and increase the voltage on the board pcb to the required +5 volts to operate the game. When it fails you end up with bad resistors at R29 and R30. It is generally caused by bad edge connections. You must use a meter to adjust the board manually to the correct voltage +5 volts using the Potentiometer next to R29 after doing this modification.
 
Thanks Jimjaycee..

Confused.. the board is showing the correct output voltages..
Perhaps the diode is not REALLY necessary.. just a precaution?
I'm having trouble understanding the circuit fully.

I checked out all the resistors on the AR board and they are all providing
resistance... Also the audio is working well on the game. Another
indication to me that the problem lays in the monitor given the X/Y Output

What could fail on the deflection board that could cause the spot killer to
come on?

Malice95
 
Next step in your chain of thing to do is remove the deflection board from the monitor.
Unplug the machine first. Of course It is always safer to discharge the CRT on your monitor
to do this procedure properly get 10-100k ohm resistors (this equals 1m ohm resistor) and solder them end to end cover with shrink wrap connect one end to the metal frame of the monitor. Use a small bit of wire and connect a flat plastic handled screwdriver to the other end of the resistors. Place one hand in your back pocket with the other hand slide the flat screwdriver tip under the suction cup (Anode) on the CRT tube. Make sure you are not touching the metal part of the screwdriver. You may hear a pop. This prevents the HV Diode in the HV cage from being damaged. Unplug all the connectors on the board remove the 2 screws holding it in place and pull out the board. Check your connectors for hairline solder cracks. Since you have it out reflow them. This may be all that is required. Take pictures of things as you go so you know how things go back together.
Jim
 
My asteroids Z output seams to be going from .4 to .6 and it would vary a little based on screen size. So that one is probably good as well.
 
Thanks for checking that Jimjaycee. I just ordered a full cap kit from bob roberts and a discharge tool. Once those get here next week I will pull the deflection and HV boards
and reflow/cap everything. Cross your fingers:)

Malice95
 
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