Hi everyone,
I'm working on a Pink Triangle Anniversary PSU, I can't find schematics or any info on the design on this so its a bit difficult for me to fully understand its workings.
The PSU switches on but it drives the motor into runaway speed. The issue started after the 12V batteries have been replaced with new ones. This is for both 33 and 45 rpm.
My understanding of how the PSU should work is:
Mains supply power to the electronics inside the PSU, the motor is driven from the big 12V (6+6) batteries and the speed control is achieved by the AC tacho attached to the DC motor.
I did check the motor separetly and suppling different DC voltages results in variation in the AC feedback so I belive the motor itself is operating correctly.
I'm able to track the AC feedback signal through the initial quad op-amp, it gets amplified and then it goes through a pair(NPN, PNP) of medium power transistors BD135 and BD136 and then it gets complicated for me as there is a comparator circuit (LM393N) two logic chips (MM74HC00N, MM74HC02N ) and a precision timer/oscillator chip (ZN1034E). All the chips have 5V supply present at Vcc pins. The collector of the PNP transistor seems to be feeding input of the logic chip.
There are two 4.01V reference voltage ics, one is sitting precisly at 4.01V the other one is attached to a trim pot for fine speed adjustment however instead of 4.01V it sits at 6.5V (adjustable with the trim pot from 6.3-7V) Those Ics have adjustable output however what is the point to have a precision 4.01V if its not set at this voltage?
I have replaced the precision timer chip however the issue remains, all the trimpots seems to be working fine. PSU is fully recapped.
Perhaps someone is more familiar with this design than me and can comment or give me any pointers.
I'm attaching a photo of the PSU and a simplified (very simplified) circuit diagram.
Thanks!!!!
I'm working on a Pink Triangle Anniversary PSU, I can't find schematics or any info on the design on this so its a bit difficult for me to fully understand its workings.
The PSU switches on but it drives the motor into runaway speed. The issue started after the 12V batteries have been replaced with new ones. This is for both 33 and 45 rpm.
My understanding of how the PSU should work is:
Mains supply power to the electronics inside the PSU, the motor is driven from the big 12V (6+6) batteries and the speed control is achieved by the AC tacho attached to the DC motor.
I did check the motor separetly and suppling different DC voltages results in variation in the AC feedback so I belive the motor itself is operating correctly.
I'm able to track the AC feedback signal through the initial quad op-amp, it gets amplified and then it goes through a pair(NPN, PNP) of medium power transistors BD135 and BD136 and then it gets complicated for me as there is a comparator circuit (LM393N) two logic chips (MM74HC00N, MM74HC02N ) and a precision timer/oscillator chip (ZN1034E). All the chips have 5V supply present at Vcc pins. The collector of the PNP transistor seems to be feeding input of the logic chip.
There are two 4.01V reference voltage ics, one is sitting precisly at 4.01V the other one is attached to a trim pot for fine speed adjustment however instead of 4.01V it sits at 6.5V (adjustable with the trim pot from 6.3-7V) Those Ics have adjustable output however what is the point to have a precision 4.01V if its not set at this voltage?
I have replaced the precision timer chip however the issue remains, all the trimpots seems to be working fine. PSU is fully recapped.
Perhaps someone is more familiar with this design than me and can comment or give me any pointers.
I'm attaching a photo of the PSU and a simplified (very simplified) circuit diagram.
Thanks!!!!
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