SD2000 help

[Unregistered]

I have changed my sd2000 damper resistors so that i can use variable resistor. I had about 270 ohm fixed and 250 ohm pot.
Since that did not work i put it back to somewhat normal. Inplace of the 12 x 270 ohm resistor I put 330 plus 56 ohm in series to get close which was about 390 ohm.
Now the machine not work. It sound ok when turn on but it does not detect. I replace both FET in the front end recieve.. but still same ..
Any suggestion anyone
Henry

[porkluvr]

big uh-oh

If you screwed up your SD2000 clone it's OK because you're a genius for getting it running in the first place. But if you've screwed up your Minelabs SD2000 then I fear for your sanity.

Besides damping the flyback pulse the damping resistor network also taps a portion of the flyback signal to trigger the blanking gate. You should put the damping resistors back the exact way they were so that the blanking gate can function properly.

Your detector still possibly won't work because without a properly timed blanking signal your receiver would have very likely experienced overload because of having a low resistance path to the coil at the same time when there was a high voltage present. You know what that means.


Maybe you should look at the 1uH coil, the clamping diodes, and the LM394, and etc... . GOOD LUCK.

[Unregistered]

Thank you for your assistance
I found the problem . It was the BS170 fet
THnks again