battery drains when i plug in jack. can not find cause

Thread Starter

ninjaman

Joined May 18, 2013
324
hello,
i have this problem with a broken guitar pedal, no schematic.
i removed a capacitor which was causing the battery to drain. when i plug in the jack lead it drains the battery again. i also, have a flip flop that activates the pedal. i put a momentary switch in place as the old was broken. the light goes off when pressed but comes back on when not pressed. i dont know what to test, how to test or what to look for. i have a basic volt meter which does diode testing as well. if i were to test a chip, what is the best way and what would i be looking for. i imagine removing the chip is best, but then do i have to make another circuit specifically to test that chip?
the chips on the board are
tc401 3bp d type dual flip flop
5222 8701 serial dac voltag output
555d not sure if this is a timer, i dont know what the d is for. i think that is provides a clock for the flip flop
mn3007 bbd delay chip, this one is sat in a socket
m5218l low noise op amp, there are five of these

can these be tested in circuit?
 

Audioguru again

Joined Oct 21, 2019
1,595
On most guitar "pedals", the circuit is turned on when a cable is plugged into a jack on the pedal and the circuit stays turned on draining the battery until the cable is unplugged.

The current from a little 9V battery for an old fashioned original 555 is about 10mA even when it is doing nothing. A modern Cmos 555 draws almost no current.
Each opamp draws a few mA each and you have 5 of them.
I did not lookup the current draw of the other ICs.
So it looks like an ordinary little 9V battery will not last long, use alkaline for the longest life.
 

drc_567

Joined Dec 29, 2008
855
... There appears to be a similar schematic on the page here:
circuit diagram
However ... need more info. Which capacitor did you remove?
One electrolytic cap is adjacent to a diode ... C23 ...Could that be the one ... 100u? Are you able to see if the diode next to it is intact?
 

Thread Starter

ninjaman

Joined May 18, 2013
324
... There appears to be a similar schematic on the page here:
circuit diagram
However ... need more info. Which capacitor did you remove?
One electrolytic cap is adjacent to a diode ... C23 ...Could that be the one ... 100u? Are you able to see if the diode next to it is intact?
Hello, I am not sure that this is the problem. It is to do with the power supply. I am currently running off the battery. what i would like to know is some method of testing using a basic multi meter. testing components on the board with a battery connected. is there no way a faulty could be found. would an oscilloscope be more use? a small one is available on ebay, i am not sure what kind would be best for fault finding.
thanks
simon
 

drc_567

Joined Dec 29, 2008
855
See if you can locate the positive lead of the 10uF electrolytic capacitor labeled C24.
With a good 9v battery connected, you should measure about 4.5 volts, with respect to circuit ground, at this pin. If you do not measure 4.5 volts at C24, then something is bad in the vicinity ...most likely a 1N4001 diode, which can be be desoldered in order to further test out.
 

Thread Starter

ninjaman

Joined May 18, 2013
324
i cant seem to get that 4.5v yet as when i connect the battery and plug in the jack the battery starts to go down straight away. i am running out of 9v batteries quickly.
it seems also that the switch is not latching. i have seen how a flip flop is used to latch the pedal on. however this is not happening. the red button comes on which means the pedal is activated and does no go off except when i hold the button closed. does the flip flop need a clock signal to latch it shut? i was thinking that maybe the clock is not working properly. i am trying to find a logical way through this.
i tried to remove the flip flop and now i am worried i am going to screw up the board if i can not remove it.
 

LesJones

Joined Jan 8, 2017
2,667
The logical way is to trace out the schematic of your unit. If it does not make sense to you then post it on this forum and there will be many members that can work out how it is designed to work. They will then suggest ways to attempt to diagnose the fault.

Les.
 

Dodgydave

Joined Jun 22, 2012
9,206
Take pictures of the pcb both sides, and put your Dvm on DC Amps, with the Positive lead to the battery and Negative to the pcb positive Terminal.
 
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