Repair: Need a little help from the experts

[grundle]

Sorry for the vague title, I can't think of anything better.

Anyway, as a few of you know, I have a non-functioning Jungle King cab here.  I'm trying to hook a computer PS up to it to see if it will power on.  I connected all of the voltages (+5, -5, +12) and the returns, but I don't know what the MRST pins should be hooked to.  It's an early Taito cab, and I've seen some references to neediing resistors, diodes and caps to hook it up, but I was wondering if there might be an easier way just to test things out, since I don't have all that at my house.

Good news is that I now get some garbage on the monitor, which is an improvement over nothing...

[BobA]

I think the manual said it was to pull the signal to active ground for a few seconds.  You could manually do that with a switch and a resistor.   They probably use a RC network to time it when it turns on.   Since the opto is in your PS you cannot sync that with monmentary loss  of power but just a switch and resistor so you don't short it directly might work to kick start it.

The resistor should tie the line to +5V and hold the MRST line high.   A n/o momentary switch between the MRST line and GND will let you take the MRST line low for the period of time that you need.

[D_Zoot]

MRST, or the Reset line, from the original power supply holds the CPU in reset until the old analog power supplies rails stabilized.  It also resets the CPU in the event the power supply drops below a threshold, for whatever reason.

It's easy to spoof the MRST circuit if you need to use a switcher these old Taito games, here's a quick method that works good:

http://www.arcadecollecting.com/info/taito_reset.htm


You can try holding the line low with a toggle switch and then pulling it high to +5v just for test purposes, but I don't know if generating a rst signal that way would be clean enough (smooth RST signal) to work properly.

The three parts you need to do it *should* be available at even a typical Radio Shack,  the diode number isn't critical, anything in the 1n4xxx series would work.


Regards,
D

[grundle]

I put +5V to it and it fired up.  I'll try to put this circuit together at work tomorrow.  I should be able to dig up everything I need there.