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Bad CRT troubleshooting


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#1 sideburn OFFLINE  

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Posted Mon Jan 11, 2016 12:15 PM

Hello,

I have a vectrex that does nothing at all when powered up so I thought I would take a shot at fixing it. The first problem is the CRT is dead so I replaced all of the capacitors on the power pcb but that didn't change anything. Hopefully someone here can answer some questions I have.

- with the logic board disconnected but switch powered on, should the back end of the crt be glowing orange? Because it is not.
I do see some voltages as high as 130v when I probe areas on the pcb near the flyback transformer and I do get a tiny spark when I discharge the crt. I'd like to know what areas to check for voltages and what it takes to have the crt glow in a normal circumstance.

The transformer seems ok, each brown lead going to the pcb is putting out 10v.

Thanks for any help!

Edited by sideburn, Mon Jan 11, 2016 12:18 PM.


#2 sideburn OFFLINE  

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Posted Tue Jan 12, 2016 8:11 AM

No one?

To simplify:

I need to know if the neck of the crt should light up/glow even if the logic board is disconnected?

Can someone with a multimeter give me the voltage readings I should expenct from the pcb that attaches to the back of the crt.

#3 juice2839 OFFLINE  

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Posted Fri Jan 15, 2016 9:59 AM

No one?

To simplify:

I need to know if the neck of the crt should light up/glow even if the logic board is disconnected?

Can someone with a multimeter give me the voltage readings I should expenct from the pcb that attaches to the back of the crt.

 

Why do you have the logic board disconnected? If you truly want to fix this you need tools like an oscilloscope otherwise your just going to be doing a shotgun repair and probably cause more damage then good.



#4 R.Cade ONLINE  

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Posted Fri Jan 15, 2016 10:09 AM

The heaters (what you call neck glow) should light if they have proper heater voltage. This is usually not related to receiving any signal from any source, but XY monitors are different and I'm not personally experienced with them.  I know some designs shut down the monitor when it lacks proper signal to avoid damaging or burning the display (spot killer).

 

You'll have to consult the service manual for that display to see what the heater voltage and pins should be. I believe the complete Vectrex service manual is online somewhere that includes troubleshooting, including scope settings and readings. It is difficult to repair without this and the scope- as mentioned it is all luck and intuition without it, which can be frustrating if you lack either.


Edited by R.Cade, Fri Jan 15, 2016 10:12 AM.


#5 Rolo OFFLINE  

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Posted Fri Jan 15, 2016 10:18 AM

Hi sideburn,

 

Quote from the service manual: "Turn brightness to minimum and measure the high voltage; it should be 5.8KV+/-150VDC." If you turn brightness up, HV goes up considerably. 7KV could well be the truth. Tv-sets with big CRTs sometimes really are using 20 to 30 KV. But this is just voltage, not current or power.

 

Schematics:

Pin 1: +170VDC

Pin 2: +50VDC

Pin 3: GND

Pin 4: 12VAC (there it is: filament) 

Pin 5: -30VDC

 

Concerning the disconnected logic board, I'd say filament voltage should be unaffected. Indeed, I'm always only switching off the logic board, when I change cartridges. I leave my filament burning, to save CRT lifetime. But I have to look it up in the schematics, to be sure. I can't do that now. Please give me some time...

 

-Rolo



#6 sideburn OFFLINE  

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Posted Sat Jan 16, 2016 4:23 PM

Thanks. I have disconnected the logic board for now while I sort out why the monitors not firing up. I do have the tools to repair. Logic probe, multimeter, oscilloscope, etc.

#7 juice2839 OFFLINE  

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Posted Sat Jan 16, 2016 6:33 PM

Thanks. I have disconnected the logic board for now while I sort out why the monitors not firing up. I do have the tools to repair. Logic probe, multimeter, oscilloscope, etc.

 

 

Hook everything back up. Are you getting sound and game play, but no picture or is it completely dead?

 

If it's completely dead then use your O-scope and check for a clock to the 6809. If the clock is good then check Ay-3-8912. I have seen that go bad more then once and cause a dead unit.

 

If it plays blind and has high voltage then it's probably the 4066 or op amps on the logic board (Check the signals with your o-scope). If it does not have high voltage then it's probably the 555 or the hot transistor.


Edited by juice2839, Sat Jan 16, 2016 6:34 PM.


#8 sideburn OFFLINE  

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Posted Sat Jan 16, 2016 7:27 PM

It's completely dead. No sound. No picture. So far the voltages I have tested are good. Since the CRT is not even lighting up I figured I don't need to have the logic board connected why troubleshooting the CRT issues. I re-capped the pcb.

#9 juice2839 OFFLINE  

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Posted Sat Jan 16, 2016 7:36 PM

It's completely dead. No sound. No picture. So far the voltages I have tested are good. Since the CRT is not even lighting up I figured I don't need to have the logic board connected why troubleshooting the CRT issues. I re-capped the pcb.

 

I'd start with getting the logic board working first myself. If you get it playing blind it makes getting the crt to work easier. You can see the game work on your O-scope with the logic board working. If your scope has XY mode. 


Edited by juice2839, Sat Jan 16, 2016 7:37 PM.


#10 Rolo OFFLINE  

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Posted Sun Jan 17, 2016 7:28 AM

So, you don't have audio, too?

You probably have more problems, than one.

 

The Vectrex should play MINESTORM with or without CRT. So you should hear all sounds, like the VECTREX-welcome-tune. Like juice2839 said, you can hook up your scope to the x and y outputs und see the video-output including the connecting beam traces, when the beam normally is switched off. I think, I posted some screen shots of that somewhere on AA.

And you should hear the deflection noise in the speaker.

 

Concerning the not glowing tube-filament, my tube keeps glowing even when I cut off the voltages of the logic board, I just had  a look at it. Do you measure the approx. 12VAC? What is the resistance of the filament-heater?



#11 sideburn OFFLINE  

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Posted Tue Feb 9, 2016 12:04 PM

So, you don't have audio, too?

You probably have more problems, than one.

 

The Vectrex should play MINESTORM with or without CRT. So you should hear all sounds, like the VECTREX-welcome-tune. Like juice2839 said, you can hook up your scope to the x and y outputs und see the video-output including the connecting beam traces, when the beam normally is switched off. I think, I posted some screen shots of that somewhere on AA.

And you should hear the deflection noise in the speaker.

 

Concerning the not glowing tube-filament, my tube keeps glowing even when I cut off the voltages of the logic board, I just had  a look at it. Do you measure the approx. 12VAC? What is the resistance of the filament-heater?

 

 

No sound.. nothing. Ive measured voltages ranging form 12v to 50v I haven't checked the board connecting to the neck of the crt yet. Where are you measuring 12VAC?



#12 Rolo OFFLINE  

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Posted Wed Feb 10, 2016 4:50 AM

Schematics:

Pin 1: +170VDC

Pin 2: +50VDC

Pin 3: GND

Pin 4: 12VAC (there it is: filament) CRT Socket P501 

Pin 5: -30VDC

 

If the filament is not glowing, then you either don't have no voltage or the filament is broken (resistance infinite).



#13 juice2839 OFFLINE  

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Posted Wed Feb 10, 2016 1:25 PM

It's extremely rare (IE: I have never seen a bad filament on a vectrex and I have worked on more than I can count). Again I suggest you get the logic pcb working then go from there. If your not getting anything (dead) try the ay-3-8912 sound chip first. If this chip is bad you get no video, no sounds and no joysticks. I have seen this fail a few time with your symptoms. If you get it to play blind then you can go from there and get your display working. I have a spare CRT I'd part with if you indeed needed one, but I bet you don't.



#14 sideburn OFFLINE  

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Posted Wed Jan 18, 2017 11:41 PM

Hi sideburn,

 

Quote from the service manual: "Turn brightness to minimum and measure the high voltage; it should be 5.8KV+/-150VDC." If you turn brightness up, HV goes up considerably. 7KV could well be the truth. Tv-sets with big CRTs sometimes really are using 20 to 30 KV. But this is just voltage, not current or power.

 

Schematics:

Pin 1: +170VDC

Pin 2: +50VDC

Pin 3: GND

Pin 4: 12VAC (there it is: filament) 

Pin 5: -30VDC

 

Concerning the disconnected logic board, I'd say filament voltage should be unaffected. Indeed, I'm always only switching off the logic board, when I change cartridges. I leave my filament burning, to save CRT lifetime. But I have to look it up in the schematics, to be sure. I can't do that now. Please give me some time...

 

-Rolo

 

 

Hi Rolo,

 

Are you referring to the 5 wires going to the yoke? I couldn't figure out what pins you are referring to from the schematic.

I took readings off the 5 wires going to the yoke and I am reading:

 

Brown wire: +132VDC

Black wire: 0VDC

Gray wire: 0VDC

Blue wire +10.4VDC

White wire: +49VDC



#15 Rolo OFFLINE  

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Posted Sat Jan 21, 2017 7:44 AM

I've been on a business trip. Sorry for the delay...

 

I was referring to the pins of transformer T502 on the power board (Pins arranged in a circular shape, Transformer inside a metal case). Those are leading to connectors EP501 to EP505 on the board and finally to the CRT-socket.

Don't ask me for colors of wires, since I don't have an open Vectrex here at the moment. And wire colors might change anytime during production.

Don't forget: filament heating is AC! Change your voltmeter from DC to AC-mode or you get a wrong 0V reading!

You must see a red-glowing filament heater inside the CRT.

:)






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