Optic Board repair

[Trimoor]

I got a used Imperial trackball, but I'm having trouble with the mouse hack.

One axis works perfectly, but the other doesn't work at all.
However, if I swap the optic board on the non-working axis with a different one, it works fine.
This leads me to believe the optic board is bad.

The board is a model P2240, the kind with a single chip and 3 resistors along with the IR diodes.

I measured the voltage at the IR reciever, and it checks out fine.
But when I measure the voltage at the pins, it's bad.

I have a few options on what to do next:
Should I wire the mouse directly to the reciever and screw the chip?
Should I buy  a new board/chip?

What does that chip do anyway?
Other boards don't even have them.

Thanks!

[brained]

http://www.arcadecontrols.org/yabbse/index.php?board=1;action=display;threadid=21725;start=msg175770#msg175770

Did you measure the voltages with this suggestion that oscar gave... This helped me a lot..

Well when I was making my trackball hack I was thinking the same, just using the receiver,  but then some how It started working!!   weird !!

You say that the connection works fine with other optic board...... hmmm...

[fixumdude]

What type of mouse is it?  I initially used a serial mouse hack on my wico trackball.  I found it had enough voltage to run one optic board, but when I plugged in both the voltage dropped to less then 3 volts.  Sometimes one axis would work sometimes neither would work.  I switched to a PS/2 mouse hack and haven't had any more voltage problems.

If the same board is always bad you can order a couple of optic packs from newark electronics or digi-key and replace the ones on the bad board.  I've done this with a few Atari optic boards and have gotten most of them to work again.  It may not be worth it for imperial boards since you can get two good ones on e-bay for $12.50 plus shipping (the optic packs run about $1-$2 each plus shipping plus a $5 charge for orders below $25 and then you have to do all that soldering).

[Trimoor]

The voltages measure fine at the sensor, but not at the output pin.

This make me think the chip is bad.
What does it even do?

It's a ps/2 mouse, and it runs two boards fine, just not the broken one.

Should I solder the sensors directly to the output pins?
Or does that chip actually do something?

[fixumdude]

One of the engineers at work told me what the chip does but I forgot what he said.  I will take one of the boards in tomorrow and ask him if he thinks it will work without he chip in the circuit.

I'm pretty sure he said the resistors were important to get the signal to the right levels and to protect the LEDs from burning up from too much current so you may not want to bypass them.  I'll check on the chip though.

[fixumdude]

My friend said that the chip was just a buffer chip and you should be able to bypass it and see what happens.

[Trimoor]

It works fine without the chip.
I guess mice have buffers built in.

Thanks all!