Newbie

[dibstwo]

Anyone who can help with a Garrett Ace 250 problem? It has been great for the past few years and just went to only being able to detect coins at 2" in air. Detects nothing at 5" regardless of size. Been told it is probably the coil and checked the resistances. Told they were within spec. Have a digital scope, etc. Anyone suggest any tests? Detect alone and can not borrow a coil to check by substitution.

[pito]

show what you have on oscilloscope, U8 pin 6, U2 pin 5, U12 pin 1 & 4.

[dibstwo]

Thanks Pito. Found the op amp, OP 37 and with no metal presnt it is showing 6.65KHz pk-pk 340mV. With metal pk-pk 6.5V, about same frequency. U2 and U12 appear to be different (LMC60, LM396?) but will trace through crt to check - just off to work.

[pito]

show PCB picture
6.65KHz pk-pk 340mV. With metal pk-pk 6.5V, = OK,
it is sine wave ?
4016, pin 5, 6 ?
KT1, KT10 ?

[dibstwo]

It was a sine wave, it clipped at 6.5V. Noticed that the presence of metal only altered the waveform at short distances, less than 3". Just back from work and I intend to scope the crt at the points you suggested. I attach a photo of the pcb. Once again, thanks for the help.

[dibstwo]

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

KT1 sine wave pk-pk 260mV 6.8kHz, with metal 6.6V 6.8KHz square wave
KT10sine wave pk-pk 220mV 6.8kHz, with metal 6.6V 6.8kHz square wave

[pito]

U3 pin #1 = 8V ?
416 ,5,6 = 8V square wave, shifted 90 degrees
KT1, KT10 = similar to this


bottom line, green pulses

U8 pin #8 = 8V ?

[dibstwo]

U3 pin 1 8Vdc
4016
pin 5 just noise, with or without metal
pin 6 noise without metal, distorted square wave pk-pk 6.8V, 6.8kHz with metal

KT1 and Kt10 as before, sine wave without metal, square wave with but distorted on KT10 and metal vitually touching coil.
Any thoughts Pito regards coil or pcb?
Thanks, Jerry

[pito]

Any thoughts Pito regards coil or pcb? = let see the results mentioned below tests
For now without coil.
U2 pin #6 = 8V DC ?
Pin #5 = square wave 8V?

U12, pin1, 7 = square wave 8V?
pin 8 = 8V DC ?

U8 pin #8 DC voltage ?

[dibstwo]

Without coil, U2 and U12 were just noise at pins indicated. U8 pin 8 was 7.4V dc

[pito]

U2 pin 8 = 8V DC = U2 and U12 were just noise at pins indicated = ?
with coil C31 = ?

[dibstwo]

Without coil
U2 pin 6 8V dc, pin 5 noise, pin 8 1.5Vdc

With coil
C31 sine wave/pulse pk-pk 31.8V 6.65kHz
Pins described as noise were mainly 50Hz (mains power)

[pito]

C31 sine wave/pulse pk-pk 31.8V 6.65kHz = perfect , Tx coil ok


C24 ,no metal close to the coil = ?
U8, pin 6, no metal close to the coil = ?

C38 = ?

U12;
pin 8 = 8V DC ?
pin 3, 6 = sine ?
pin 1,7 = square wave 8V ?

[dibstwo]

C24 noise
U8 pin 6 noise

U12
pin 3 sine wave 3.4V pk-p k
pin 6 sine wave 6V pk-pk
pin1 noise
pin7 sq wave 3V pk-pk
pin 8 8V dc

Having problems finding C38, my eyes not too good! All waveforms at about 6.65kHz.

[pito]

C24 noise = with metal close to the coil ?
U8 pin 6 noise =with metal close to the coil ?

U12
pin 3 sine wave 3.4V pk-p k = not perfect but ok
pin 6 sine wave 6V pk-pk = not perfect but ok
pin1 noise = not good, should be the same as on pin 7
pin7 sq wave 3V pk-pk = not perfect but ok
pin 8 8V dc = ok
--------------------------------------------------
U12
pin 2, 5 ?

U8
pin 3 DC = ?
pin 7 DC = ?

U9
pin 5 = resistance to the ground ?
pin 6 = resistance to the ground ?
---------------------------------------------------


C38