F1A4 Mods anyone?

[fo0bar]

Well LM311 is used for this job in a later model, so it is possible that I misread the scraped away marking.

Actually you're probably right, it likely is the 1011. Looked over the datasheet again and found typical applications which matched the configuration here - along with a phrase "When the emitter is used as the output, the collector istypically tied to V+ and the load is connected to groundor V–."

I guess it was the output transistor that confused me - I'll stick with LT1011 after all!

[Mechanic]

Well LM311 is used for this job in a later model, so it is possible that I misread the scraped away marking.

[fo0bar]

Ahhh, try lt1011 instead.
Bit of a dyslexic typo! I need to fix that up in the source.... Thanks for finding that one!

Hrm, maybe I'm missing something...?

Here's the datasheet for the lt1011 - https://www.analog.com/media/en/tech...ets/lt1011.pdf

On the board, Pins 7 & 8 are connected - according to the datasheet, this is the output (pin 7) and V+ (pin 8 ), both connected to +5v. It just doesn't seem to fit in the circuit...

On the datasheet however, it states "Pin compatible with the LM111" - So I checked out the LM111/LM211/LM311 datasheet - https://www.ti.com/lit/ds/symlink/lm311.pdf.

The LM111/211/311 seem to fit much better in this circuit, with pin 1 being "EMIT OUT" connected to MCU[16], Pin 7 being "COL OUT" connected to +5v, and pin 8 being VCC+, also connected to +5v.

I'm not sure how they could be "pin compatible" with such different designations. Again, maybe I'm missing something...?

Anyway, I'm now starting to think it's a LMx11... What are your thoughts, Mick?

[Mechanic]

Ahhh, try lt1011 instead.
Bit of a dyslexic typo! I need to fix that up in the source.... Thanks for finding that one!

[fo0bar]

U504 is an LT1011, used as part of it's adc setup.

Hi Mick!

Yes, This is what I've currently got for that part - though it just doesn't seem right as according to the datasheet, pin 7 is the output and pin1 is GND - however on the board, pin 7(output) is connected to the +5v rail (via pin 8 ), and pin 1(gnd) is connected to MCU[16].

...Does this seem right to you? I've never come across an comparator or opamp output directly connected to +5v before...?

[Mechanic]

I'm not Zed, but I'll give you a few clues..

U504 is an LT1011, used as part of it's adc setup.

U503 I have as 277, however 272 could be more likely. I'll keep an eye out and confirm that one. Worst case, it can always be decapped!

And from the pulse board, yes they are 5534.

Cheers Mick

[fo0bar]

G'day fo0bar

Nice one mate,you been busy...which chips are you struggling with ?

Hi Zed, Sorry for the extremely delayed response - lockdown shifted my lifestyle and I've hardly been fiddling with detector stuff or checking forum messages.... But this hard lockdown's hopefully ending soon which means I need to get cracking on it all again!

I'm having issues figuring out what the SO8 IC is in line with the DAC and nearest pin 20 of the MCU. I think it's U504. Seems to be a balanced opamp but nothing I can find looks right in the circuit.

Also the SO8 near pins 3 & 4, I think that one's U503. I suspect it's a TLC277C but I'm unsure:

And on the power/clock/pulse board, I'm unsure what the RX preamps/amps (4 SO8's after the LM394) are exactly - I've assumed NE5534's for the time being as they pin out correctly:

If you've got any clue or hints, I'd be all ears!

I've got pretty much every other major component figured out (I think/hope!), leaving a handful of passive components to double check. I've now also cloned the external PSU controller and whipped up a PCB front panel design to accommodate the L3 mods. Looking forward to all my mistakes being manifested in magic smoke....

[ZED]

Hello james

Your problem sounds like Karma.

[Mechanic]

Try and get hold of Downhalo, he seemed quite knowledgeable on all things f1a4 and had lots of diagrams and stuff.

[JamesAU]

having a weird issue with my F1.

This morning i switched it on to start detecting and it isn't going through its 3 tone start up process, it just makes a single threshold tone and does nothing.
also noticed a day before that it had no sensitivity to targets.

Any idea's on what might be jacked up? probably trash now but figured i would ask before i harvest it for parts.

[ZED]

fo0bar said

"I've also managed to "see through" the paint and trace out/reverse engineer the entire circuit & boards in kicad and have got the boards cloned very accurately, almost ready for production though there are 2 or 3 IC's I'm still yet to properly identify."

G'day fo0bar

Nice one mate,you been busy...which chips are you struggling with ?

[JamesAU]

wow, sounds like you've made great progress, colour me intrigued!, hope you can find those missing IC's and get them rolling out.

Completely understandable, And i very much agree. I've done a couple of the mods myself, like multiple frequencies, gain, all the stuff, like threshold and tone, took me a long while to get them just right, except for the timings.
Thankfully one of the more well known modders was willing to point me in the right direction to save me from letting the smoke out lol.

I'll shoot you a PM.

[fo0bar]

G'day James,

Sounds like you're in for some fun and frustration. Just remember to "measure twice, cut once". I've got hot-snot plugged holes on my front panel due to getting a bit enthusiastic with the drill...

I've now got a far greater understanding of the F1A4 with all common mods taken care of, though I do have to credit a great deal of my knowledge to another very generous person who's been very helpful along the way. I've also managed to "see through" the paint and trace out/reverse engineer the entire circuit & boards in kicad and have got the boards cloned very accurately, almost ready for production though there are 2 or 3 IC's I'm still yet to properly identify.

I'd be happy to answer questions via PM rather than publicly - while I've done a great deal of work on this myself, a lot of information was also given to me on good will and the well-known mods aren't my work/research to publish.

[JamesAU]

I've now received the F1 and carefully removed the paint to expose some of the tracks and lands next to the EEPROM. I've also tested around the place with a meter to check continuities.

Looking at a photo from geotech of the eeprom, there's 6 little lands. I have a feeling on some revisions there may be a couple of 0R resistors there covering two traces, which could be what are being referred to in the post you reference above. I'm working on a REV3.2 board.

Firstly a little disclaimer - I'm sharing this information as there seems to be a lack of it available. It seems in the past there was a bunch of secrecy surrounding these mods but I've emailed detectormods asking for info and he's said he avoids working on them now, and I can't find anyone else still active on forums that's actively modding these to ask, so I'm assuming no one's really trying to rake a profit off these mods anymore. Nonetheless, if anyone loses their shirt over this info being public, just let me know and I'll be happy to remove it. I'm not out to rustle any feathers.

Anyway here's my findings:

- The top two are connected to VCC.
- The left middle goes up to the EEPROM. The right middle goes down under the IC below the EEPROM.
- Both the left and right middle are connected to VCC via traces to the lands above them.
- The bottom two are connected to GND.

Here's a super professional drawing based on the one I found here at geotech:
[ATTACH]46931[/ATTACH]

This is leading me to believe that I'll need to:
1. Cut the traces which are connecting the middle two to their respective top lands (shown in green)
2. Switch the middle two between their corresponding top/bottom (top == high & bottom == low)

If I'm correct, this will give 4 possible combinations of timings ....A level 3 modded F1A4 pictured at https://www.prospectingaustralia.com...c.php?id=18986 shows 4 levels of timing (big/gen/std/fine), but I'm unsure of what the other knob does. Most other modded machines show 3 levels of timings so maybe I've got something wrong here... At some point I'll see what my scope tells me but I might have to wait for my logic analyser to arrive before being able to see the big picture.

I'm probably going to wait a little while before testing this theory...Planning to take the machine out this weekend and would really like to get at least one use out of it before potentially releasing the magic smoke.

Hi Fo0bar,

Did you ever have any luck with timings? btw you are correct in that if you mod the unit as such you will have 4 different timings, as seen on the L3 units
The other knob you mention is for Frequency, by adding/subtracting capacitance you can change the frequency at which the machine operates (as i'm sure you know)

You're on the right track for gain also, i noticed you had scraped the gain resistor off.

any info you're willing to share here or via PM would be appreciated, as i've just purchased an F1 myself and would love to mod it up a bit.

- J.

[fo0bar]

hi fo0bar, if you can can get access to a media blaster soda blasting makes short work of that epoxy paint, strong enough to shift paint but gentle on the boards and components.
there is a thread somewhere talking about removing that paint.

Thanks sinclairuser - great suggestion! I'd searched the forums for a solution but again maybe my search skills were lacking. I'd been considering asking a couple of people I know whether they'd be OK sticking a "foreign" object in the x-ray machine at their practice, but that wouldn't help with any component markings (that hadn't been ground off by ML) so perhaps soda blasting would be a better alternative.

Also, looks like a battery/PSU mod has moved its way up my list of priorities. Took it out Castlemaine region yesterday and barely squeezed 4 hours out of a set of Energizers, which doesn't seem right. No way I'm taking kg's of D's on a multiday trip - going to look at squeezing in 4x18650's dual parallel, with switchmode regulation @ 6v. I'm hoping the 10mV switching ripple doesn't affect its performance.

I've also observed the stock-standard pulse timings on a scope; Interestingly different to anything I've seen mentioned here on GT - a 150uS pulse, followed by 5x 25uS pulses. Hadn't seen that mentioned anywhere.