Newbie

[dibstwo]

U8 Pin 6 with metal close to coil, sine wave 6.65kHz, clips at 7.2V when metal very close
C24 noisewith or without metal
U12 pin 2 noise pin 5 noise
U8 pin 3 4V dc pin 7 8V dc
U9 pin 5 193k ohm pin 6 141k ohm

U12 pin 1 should have a similar output to pin 7, just phase shift and different amplitude? Measured pin 1 at 8V dc, high reistance to either rail.

[Carl-NC]

4016 pin 6 sine wave (distorted, more like a rounded square wave) pk-pk 880mV 6.65kHz, with metal more like noise
4016 pin 5 noise only, with metal, no change

Sounds like this is the problem. Both clocks should be fairly nice looking 8v square waves. Make sure the virtual ground is working (U13-pin5 = 4V).

[pito]

U8 Pin 6 with metal close to coil, sine wave 6.65kHz, clips at 7.2V when metal very close = what you have on pin 1 U8 in that case ?
U12 pin 2 noise pin 5 noise = missing 4V, show picture another side of PCB

working (U13-pin5 = 4V). = U8 pin 3 4V dc pin 7 8V dc


show a photo of the other side of the PCB, no connection between these points = damaged track or oxidation, how old is the PCB?

[dibstwo]

PCB is in good order, nosign of mechanical damage or corrosion, etc. R50 is 4Vdc either side. The pin on U13 is not connected to PINS 1 or 6 of U2. The pin of U13 is 4V dc, pin 1 of U12 is 8Vdc and pin 6 iI s 4V dc.I have always stated the ac conditions when asked unless asked for dc conditions - sorry if any mix up.

[dibstwo]

Hi Carl-Nc,
Thank you for your reply. I checked the virtual earth and it is 4Vdc. Will do some more checks on the inputs/outputs of the 4016.

[Carl-NC]

Focus on the U12 comparators.

[pito]

solder wire jumper from right side of R50 to U12 pin 2 and check what you have on pins 1 and 7 with oscilloscope

[dibstwo]

Thanks Pito, will do as soon as back from work later today. By the right hand side, do you mean the side nearest U2 in the photo of the pcb? Just want to be 100% sure.

[dibstwo]

Hi Pito, just done some dc checks before leaving for work. The connections are OK, no breaks. As no voltage drop across R50, is it safe to assume that the next part to suspect is U12?

[pito]

mean the side nearest U2 = U12
next part to suspect is U12? =U12 is not yet suspect but connection of it to 4V. Before making a jumper re-solder the pins of U12 because bad solder connection can be invisible, just touch pins with soldering iron.

to be save, instead of the wire jumper you can use 100 ohm or similar resistor


The pin on U13 is not connected to PINS 1 or 6 of U2. = it is hard to see any traces on your picture from post # 19, maybe it is a 3 layer PCB ?

[dibstwo]

SORTED!!!!
Thanks Pito, it was a dry joint at pin 5. It now detects my keys at about 1ft and coins at 8 inches. Back to normal!

[pito]

Good