TGSL-EDU

[Silver Dollar]

They should be -V to ground as they actually pull up to ground from the minus supply.

4" it sounds like my Bandito! I had 10" and cleaned the PCB and now 4". I noticed low amplitude
to a target one one side of the first filters. My plan is to inject a signal and see how it looks following
it all the way through the filters. Unfortunately there is no amplitude measurements you can do as
the signal is changing. That's why I'll use a 10 hz signal and compare GEB to Disc to find the problem...

Have a look at GEB and Disc vs RX too to see if you are sampling at the right times. Then you can look at
the outputs of each filter and wave a target and compare amplitudes. The sens not working is a clue. Mine
chatters above 8 on the sens pot so you are missing some gain somewhere or one channel is missing.

I see ~ 40 mv of noise at the input of the comparitors and the sens goes lower than that so you can hear chatters.

Poke around a little and tell us what you find.

[Davor]

@Daren, the level is fine for gating FETs, but I see glitches originating from U102 (I guess) that are not supposed to be this big. Could you check U101 and U102 decoupling capacitors?
These glitches are far too big for mere FET charge injection so there must be something else. In case it is in fact charge injection - your FETs are fried.

[Daren]

Got it to work! Haven't test it well, but not beeping and the range is fine...
@manny77: You were right I just did not listen.... I rather refused to believe... The damn FET ARE swapped inside. The marking on them is wrong!!! Had to take them out and test... manny77 thanks.
Thank you all for the support.
See the FET here

[manny77]

Hehe! Very well! This thing drive me crazy that time...not easy to understand the problem because everything is correct. Anyway i point silverdog to this problem...he said that place a paper with information for those fets in tgsl kits...but he don't....

[Davor]

So the FETs were not fried, but the pins were swapped.
FETs are easy to check on a multimeter (MOSFETs are not). Using a gate as a common electrode you may observe a diode-like behaviour towards source and drain (just follow the FET symbol arrow).

[Daren]

Davor, that is exactly what I did (after googling it....); Just tested the two diodes, that clearly proved that that the gate was swapped.
( My next step was to replace all active parts one by one... Thankfully never came to that.)
I reverted the mod I did before (removing caps, diodes, adding reversed diodes). With the mod I was not able to crank sens to the point that detector chatters. Now I have just the sens pot hooked up to -V and left 1Ms in place to 470Ks.
Range: 30cm with the wedding band, 22cm (8.5 inch) with the US copper penny. The disc works great too.
The signal on the U101 pin7 still looks choppy on the top, but who cares... I can't explain it...
Thanks!

[Silver Dollar]

I'll have to check my FETs now..

[paku]

is that same transistor BF245B and F245B

[Daren]

I don't know; I could not find anything on F245B

[ice413]

Hmm, anybody know if the fet's still reversed ? Or if the PCB silk are wrong ?
I got my kit from Silverdog last friday, and start soldering today. It would be nice if i could place
the components correct from start.
There was no note in the envelope i got.
Here's what my PCB looks like:

[bernte_one]

hello ice

just take the datasheets of the parts you are not sure
for example in case you take 2n2907 in metal version the emitter ist where the metal pin is
if you take the plastic case variant you have to rotate the part compared to the silk screen print

[ice413]

Thanks .
I have the metal version, and will check how they work tonight.

[Daren]

>>FETs are easy to check on a multimeter (MOSFETs are not)
Google it

[Daren]

>>FETs are easy to check on a multimeter (MOSFETs are not)
Google it

I used this method to locate gate:
http://www.allaboutcircuits.com/vol_3/chpt_5/3.html

[ice413]

Everything on my TGSL-EDU is OK, nothing reversed.
Now i also tried it, with 2piece of 13mH degauss-coil from 14" monitors
Work OK. So next step for me is to make som 6 & 6.5mH coil and zero these.
Just waiting for my oscilloscope and LC-meter i've just ordered.