Hi all. I've ran into a fault with a home built VCO module which I can't seem to locate.
When I plug in it's power supply -12v +12v 3a it shorts across it's rails. I went to buy a new power supply today as I thought it must be that, i checked the supply befor plugging it in and there was no fault, I then plugged it into the MFOS dc converter and there was still no fault. I plugged it in for a few seconds to the module and it shorted straight away, and now the power supply is broken.
When there is no power supply plugged in there is no short accross any of the rails. So I thought it must be a resistance problem, incorrect resistor somewhere. Checking the resistance accross the rails I get these readings -12v to 0v = 43k. 0v to +12v = 6.5k. -12v to +12v = 42 k.
I went around the circuit looking for the 6.5k elsewhere other than on the +12v supply points and found it at R1(1). Disconnecting R1 (1) gve me 10k resistance between 0v and +12v.
I'm not sure if i'm on the right track with trying to find the fault.
I have taken out all Ic's to rule out them. I disconnected the pots to rule out them.
When I first had the circuit made it worked fine, however it gradually broke down. It's first symptom was the triangle wave would only show up as a saw wave, thus the sine wave only had the fall part of it's wave. I continued trying to check and calibrate to no avail. I discovered that the output pins 1,8 and 14 of U4 all went to 0v, after this I was reading shorts across sine, triangle, ramp and square outputs with 0v. Further testing culminated in U6 shorting across pins 1-4 and going up in smoke. Then my first transformer shorted out for good.
I know I've been making some mistakes with power supplies so this latest incident has forced me to buy a proper dual rail bench supply which will make diagnosing/testing safer.
I can give resistance readings off the circuit, I've checked all over the circuit and nothing is going to 0v it shouldn't be. I will have my bench supply on Tuesday when I wish to resume testing. However I though as i'm stumped maybe you folks could point me in the right direction.
Thanks
Darren
below are attached schematics and a link to the VCO build notes from MFOS
http://musicfromouterspace.com/inde...G=VCFJAN2006/VCFJAN2006.html&VPW=1386&VPH=538
When I plug in it's power supply -12v +12v 3a it shorts across it's rails. I went to buy a new power supply today as I thought it must be that, i checked the supply befor plugging it in and there was no fault, I then plugged it into the MFOS dc converter and there was still no fault. I plugged it in for a few seconds to the module and it shorted straight away, and now the power supply is broken.
When there is no power supply plugged in there is no short accross any of the rails. So I thought it must be a resistance problem, incorrect resistor somewhere. Checking the resistance accross the rails I get these readings -12v to 0v = 43k. 0v to +12v = 6.5k. -12v to +12v = 42 k.
I went around the circuit looking for the 6.5k elsewhere other than on the +12v supply points and found it at R1(1). Disconnecting R1 (1) gve me 10k resistance between 0v and +12v.
I'm not sure if i'm on the right track with trying to find the fault.
I have taken out all Ic's to rule out them. I disconnected the pots to rule out them.
When I first had the circuit made it worked fine, however it gradually broke down. It's first symptom was the triangle wave would only show up as a saw wave, thus the sine wave only had the fall part of it's wave. I continued trying to check and calibrate to no avail. I discovered that the output pins 1,8 and 14 of U4 all went to 0v, after this I was reading shorts across sine, triangle, ramp and square outputs with 0v. Further testing culminated in U6 shorting across pins 1-4 and going up in smoke. Then my first transformer shorted out for good.
I know I've been making some mistakes with power supplies so this latest incident has forced me to buy a proper dual rail bench supply which will make diagnosing/testing safer.
I can give resistance readings off the circuit, I've checked all over the circuit and nothing is going to 0v it shouldn't be. I will have my bench supply on Tuesday when I wish to resume testing. However I though as i'm stumped maybe you folks could point me in the right direction.
Thanks
Darren
below are attached schematics and a link to the VCO build notes from MFOS
http://musicfromouterspace.com/inde...G=VCFJAN2006/VCFJAN2006.html&VPW=1386&VPH=538