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


chiil

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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.

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Chiil:  Thanks for sharing this information.  I personally would be interested in following their work and progress.  Do you have a link to their site that you care to share?  If I had a second TDI SL or a used version in addition to my current one, I might be willing to try some of the circuit mods.  However, with only one in my collection, and "old man fingers", I hesitate to perform the circuit mods.  None the less, it is interesting to learn more about these experiments.  Again,  thanks for the info. 🙂

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I like the idea of separate power supplies for different functions, but question whether or not  it can be done. As far as running 16v...I've done that for a few years with no ill effects. I definitely would not put 18v thru mine, even for short periods. The capacitors are rated for 16v, so limiting your voltage to 16v is all the protection you need. In the field, I doubt anyone

could tell the difference between 16v and 18v.

Jim

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There have been several threads here on this topic.  Some kind of search should find them.  The late Reg Sniff was the guru of TDI mods and he posted quite a few things here, as well as other forums and possibly hardcopy publications.

I recall there were different versions of the TDI/SL and that some mods work for some and not others.  So I don't think every garage mod works on every TDI/SL.  I also recall Carl Moreland (who had a hand in its development at White's) warning against too high of a voltage but I don't remember exactly what his recommended threshold was.  That would be a good thing to look up.

I also modded a battery pack with an external 4-pack to be able to run 12 AA cells in series.  I bought some dummy batteries (basically shorts) so I could choose 8, 9, 10, 11, or 12 cells in series.  On top of that I did this specifically to use NiMH rechargeables which, very soon after having been charged, come down to ~1.4V; thus 12x1.4V = 16.8 V which I think is below Carl's max recommended potential.  (NiMH's have a gradual decay falloff of 1.4V-->1.2V which is their nominal operating range so typically they aren't even as high as 1.4V for long.)

If I recall (and don't trust me on this but better to read all the posts), my TDI/SPP was a version which couldn't be helped by increasing the voltage.  There also was some discussion (disagreement?) as to whether running with Ground Balance set to 0 (off) would improve depth.  The consensus was that it would and that certainly is the case with my /SPP.  But because of the different factory release versions maybe that was also dependent upon the particular version -- IDK....

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Cascade: Here's the link, hopefully I'm not breaking any rules posting cross-threads from other forums.  I use Google Chrome's (right-click) translate to english to convert the text.

https://www.forum-sud-prospecteurs.com/t7997-Adaptation-TDI-SL.htm

Definitely a lot of info posted in our forums - just don't recall some of the specific ones being mentioned in the above link.  Maybe I haven't looked hard enough.  I remember hearing about the sweep speed mod, and the battery pack.

 

edit: one more thread about lowering the pulse delay below 10uS.  I believe it was discussed in our forums, or sending it off to Reg to perform the mod.  However, this individual shows where/how he performed the work on the PCB, specifically for the SL version.

https://www.forum-sud-prospecteurs.com/t9026-White-s-TDI-au-dessous-de-10us.htm  

 

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21 hours ago, Geotech said:

The original TDI was limited to a max battery voltage of 16V. I designed the SL so it could take 20V and will probably be OK up to 25V. That's the rating of the power supply caps and anyone not comfortable running caps all the way to their rating (I'm not) can swap them out for 35V caps. The next limitation are the voltage regulators which have a max rating of 30V.

Wow...that's the first I've read that the SL will handle 5 li-ion cells (21 max volts). That may be a game-changer for the SL. Many thanks!

Jim

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23 hours ago, GB_Amateur said:

There have been several threads here on this topic.  Some kind of search should find them.  The late Reg Sniff was the guru of TDI mods and he posted quite a few things here, as well as other forums and possibly hardcopy publications.

I recall there were different versions of the TDI/SL and that some mods work for some and not others.  So I don't think every garage mod works on every TDI/SL.  I also recall Carl Moreland (who had a hand in its development at White's) warning against too high of a voltage but I don't remember exactly what his recommended threshold was.  That would be a good thing to look up.

I also modded a battery pack with an external 4-pack to be able to run 12 AA cells in series.  I bought some dummy batteries (basically shorts) so I could choose 8, 9, 10, 11, or 12 cells in series.  On top of that I did this specifically to use NiMH rechargeables which, very soon after having been charged, come down to ~1.4V; thus 12x1.4V = 16.8 V which I think is below Carl's max recommended potential.  (NiMH's have a gradual decay falloff of 1.4V-->1.2V which is their nominal operating range so typically they aren't even as high as 1.4V for long.)

If I recall (and don't trust me on this but better to read all the posts), my TDI/SPP was a version which couldn't be helped by increasing the voltage.  There also was some discussion (disagreement?) as to whether running with Ground Balance set to 0 (off) would improve depth.  The consensus was that it would and that certainly is the case with my /SPP.  But because of the different factory release versions maybe that was also dependent upon the particular version -- IDK....

The main two mods reg recommended were the Sweep Speed mod (mod 1). That mod applies to all SL's regardless of date. The second mod was to increase the sensitivity, and that mod was adopted by the factory in 2015. I'm not sure which 2015 machines have it, or don't. my understanding is that all SL's after 2015 had that mod from the factory. A search should locate the posts regarding what`needs to be done to do the mods. Mod 1 is fairly simple, as the caps needing to be replaced are large, and thru the board connections, and can even be done on the top surface of the board by cutting the wires of the old caps, and connecting the new ones to the old leads. The second mod requires a decent soldering station, and some serious skills as the components are really tiny, and surface mounted. I did both and the second taxed my skills as a solderer...LOL

Jim

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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. 

 

Geotech: Thanks for the input!  Having scoured the 'internets' it seems many of the threads mention to not exceed 16V on the SL version.  That is definitely good news!  I have been undercharging my Li-On batteries to about 14.8V.  Sounds like we have plenty of headroom to bump that a bit.  I remember having looked up the components, and they didn't quite match what other were saying in the forums.  I think the caps are panasonic (1000 E FK) 1000uF, E=25V and FK series.  Voltage regulators look like Fairchild FQT7N10 - but I could be completely wrong.  All I remember is that the voltage specs didn't quite match up to what I found on mouser/digi-key.

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