Tech: player 1 joystick analog X needs work

[jasonbar]

Howdy-

I just installed a Console5 PreAmp buzz reduction kit. It seems to have cut the buzz altogether--I hear just faint deflection chatter--very nice!

However, I boogered something up a little in the process.

Player 1's joystick X is no longer responsive. Y works, but not X. I popped in Sean Kelly's Multicart 2.0 (which uses naught but buttons to navigate the menu--phew!) & confirmed that player 2 X & Y work, & player 1 Y works. It's just player 1 X that's wonky.

I ran through the Vectrex logic PCB & found where the joystick analog signals go--all seems to be in order over there near the back of the PCB.

I checked GND, +5, & -5V at the player 1 controller port on pins 7-9. All OK.

I double-checked the audio circuit (desoldering GND, +5V, & -5V to isolate it--INPUT & OUTPUT are hard to get to right now, so I didn't undo those). Circuit seems OK.

Then, I desoldered the +5 V lead on the audio circuit & the Minestorm ship started spinning left. Desoldering all power lines to the buzzkill circuit mutes the sound but restores the joystick 1 X control.


Before I go & tear it all down & see what the issue is, does any of you w/ good electronics/Vectrex knowledge have any advice or idea on what might be the problem?


Thank you very much,
-Jason

[woolfman]

Well, I am not a Vectrex expert, but it sounds like there´s not enough power to support all (buzz amp kit, loudspeaker, joystick) at the same time. If you kill sound and the joystick works again, it might be power-related. What about tapping +5V for the buzz amp circuit somewhere near after the power transformator?

Did you do a cap replacement on all the boards?

[kokovec]

Not sure if you fixed this yet but it may have something to do with the MUX chip.
The joystick pots all go through the MUX and the speaker volume control pot is also tied to the MUX.
The MUX also uses the +-5V sources so you may have accidentally shorted something.
I also believe that one of the Joy pots is tied to the +5V source through a 1Mohm resistor near the MUX. You may have shorted something there.

[jasonbar]

Thanks tons, kokovec--I've been too swamped to attack this. I'm sure that my next step is disassembly & inspection of all of the parts that I touched. :]

vectrexmuseum.com/collection/_picts/vectrex-board.jpg

Please elaborate on which chip is the MUX? It seems to be, from this page ( www.vectrexworld.com/#!console/c1b0b ) the CD4052 chip.

But, my quick perusal of this image ( vectrexmuseum.com/collection/_picts/vectrex-board.jpg ), I see nothing labeled CD4052. Which one is it?

Thanks,
-Jason

[kokovec]

The one marked MC14052B

[jasonbar]

Thanks--I too had traced the circuit back to that chip--I didn't do any work in that region, but I'll check it nonetheless.........when I can find time to come up for air.... :\

Thanks,
-Jason

[jasonbar]

Good news, everyone!

Fixed this Vectrex!

It took a bit of troubleshooting to find something so very simple. Isn't that how it usually goes?


1 - I removed the no-buzz circuit (I'd built it up on a little bit of protoboard).

2 - I rebuilt a fresh circuit & installed it. Same problem. So, the culprit was not in my protoboard circuit.

3 - I reconnected the sound circuit as if it were once again a stock Vectrex. Normal speaker buzz & system sounds returned, intact. But, when I moved joystick 1 in the X direction, it now did function properly but made this super spacey zappy buzzy interference through the speaker. Interesting.

4 - I referred to the controller pinout found at www.gamesx.com/controldata/vectrex.htm

5 - I followed that pin's trace on the logic PCB to see where it went & if something was amiss along the way. Indeed, that one trace takes a circuitous (ha!) route around the logic PCB & passes right by the resistor & capacitor that get half-removed for the no-buzz mod. The joystick 1 stick X pot pin was shorted to the resistor! Visual inspection showed that I must have just barely brushed my soldering iron against a pad & smeared a bit of solder, removed a smidge of the overcoat on the P1 stick X trace, shorting them together.

All better now!

Thanks,
-Jason

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[kokovec]

Nice work