midway 90400 reset circuit problems

security0001

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i have not found any information on the components that make up the reset signal. i tested the power supply and the reset signal is testing at 2.74 volts and should be below .5v and where should i be checking to correct this problem? any help would be greatly appreciated so i can get my space invaders working. i recapped the power supply so those components are new and all voltages check out at the power supply and at the motherboard. (at the motherboard +12.02, +5.10, -5.16) the -5.16 volts will not adjust any lower(the pot has no more turn to reduce voltage) is that a bad pot or something else??

thanks
 
First, are you checking the circuit at the correct spot (banded side of zener diode)?

There's not much to the reset circuit.....a couple resistors, a zener diode, and a transistor. Make sure the zener diode is good and check the transistor (2N4123).

Edward
 
power supply reset circuit

i did check it according to elektron forge diagram (on the side closest to the edge of the board) i also checked the 1k resistor it was okay but i installed a new one anyway. the two transistors i have not taken out and checked (2n4125 and 2n4123). any ideas on where to start that might be the most likely problem. also my -5v still being a little high but the pot has no more adjustment down (is it a bad pot or is it okay??)
thanks
 
apply pressure to the board and connector where the connector attaches and see if that changes it. sometimes bad solder joints can cause those issues. you may want to just hit all the solder on the power supply and retest. had a constant rug pattern on my old SI that was fixed by this.
 
i did check it according to elektron forge diagram (on the side closest to the edge of the board) i also checked the 1k resistor it was okay but i installed a new one anyway. the two transistors i have not taken out and checked (2n4125 and 2n4123). any ideas on where to start that might be the most likely problem. also my -5v still being a little high but the pot has no more adjustment down (is it a bad pot or is it okay??)
thanks

Your -5VDC is within tolerance....I wouldn't worry about it.

Edward
 
reset circuit

i finally desoldered every component on the reset circuit and anyone that was in the same traces and tested everything and after all that (and it was the very last component) the diode had a cold solder joint ( the 1n4004 diode on the board). it is all fixed. thanks for the help.
 
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