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TDI SL Modifications I Haven't Seen Before...


chiil

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The 16V limit applied to the TDI, some people probably assumed the SL was the same. They are different designs. The FQT7N10 are FET transistors, used as reverse battery protection. Unfortunately I see they have a max voltage of 25V. It is not an easy matter to find a higher voltage rating, but would be easy to hack the board to reduce the voltage by splitting R41. It will require some documentation and photos and my SL is indisposed at the moment.

Meanwhile, anyone intending to run the SL above 20V I recommend swapping some caps. They are:

C2, C4, C5, C8: 1000uF@35V
C33, C34, C35: 100uF@35V

These are probably SMT and are buggers to get off. There are a couple of 16V caps in the audio stage but they are on a regulator that maintains 11.2V regardless of battery. I did that so audio volume remains the same if you use a bigger battery.

 

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Thanks Geotech!  Thanks some great information, especially from someone who worked on this specific product.  Here is a photo of the PCB (thanks to pjrough) - with the capacitor locations as Geotech pointed out.

2021-09-05_14-07.png

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On 9/5/2021 at 10:35 AM, chiil said:

Jim: Thanks for the info!  My machine is the SL special edition (tan box), with the later High-Q coil.  I assume I'm covered with both the mods you have mentioned. 

Chill....Mod 1 is not done on any SL from the factory. Only Mod 2 was adopted. The only way to get the increased sweep speed is to do Mod1 yourself, or have somebody do it....even on the S.E.

Jim

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  • 3 months later...
On 9/3/2021 at 8:30 PM, chiil said:

I came across a french prospecting website where some interesting mods had been done to their White's TDI SLs.... for instance:

1. Removal of resistor R86 within the gain circuit - providing a boost to the gain control.  They believe this was to make it stable, for less complaints.  Removal of this resistor provided additional gain reserve.  They had some good results with their testing.

2. Placing thick o-rings under some of the pot knobs.  Helps to add some friction and avoid dials turning themselves accidentally, especially with the above modification.

3.  With a single +16V battery pack, there was feedback that depth seemed to increase on the TDI SL.  However, this came at a cost of over-driving the 16V rated power capacitors as well as other circuits on the board.  Potentially shortening their life, by running them full time.  The moderator seems to have been able to add another battery pack in series (6V) with the 12V pack, and use a toggle switch to drive the voltage above 18V temporarily.  This "boost mode" was done as a method of improving a faint signal on-the-fly.  Just a flick of a switch, double-check that faint signal, and then back off.

Ultimately, it seems they were discussing driving the coil with it's own 18V external battery and using the standard 12V battery pack to drive the rest of the board (logic).  Basically driving the pulses in the coil without going through the voltage regulator, via a large MOSFET.  Unsure if they actually were able to do this mod.

 

Anyways, just thought they were some interesting ideas those french detectorists were messing with.

What respect to your original post, numbers 1 and numbers 2 do you have any quantifiable information about The results of disabling the R86 resistor? For example, depth increased by two inches for a target when the R86 resistor was disabled.  Item number two in you're modifications list was adding o-rings underneath the dials to increase resistance and prevent accidental setting modification or change during use. The question is what is the specification on the o-rings that were used to achieve this result? Do you have a source for the o-rings manufacturer and part number? Thank you kindly.

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On 9/7/2021 at 10:41 AM, Jim in Idaho said:

Chill....Mod 1 is not done on any SL from the factory. Only Mod 2 was adopted. The only way to get the increased sweep speed is to do Mod1 yourself, or have somebody do it....even on the S.E.

Jim

Okay. Thank you kindly.

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