Pinpointers

[timp]

Sunpow OT-MD01 pinpointer worked ok initially, then stopped!
Does anyone have a circuit diagram or know where I can get one?
Many thanks,
timp

[Skippy]

" worked ok initially, then stopped!"

Why the exclamation mark? That's the performance you should realistically be expecting from such an ultra-budget pointer.

However, it may be possible to diagnose its fault, but you would need to dismantle it and post up photos of its guts. Then, you would need some forum members to actually take some interest ... which could be a stumbling point.

[timp]

Hi, it appears to be an oscillator whose operating point is set by a micro, such that changes are measured by the onboard A/D, or possibly by measuring the resultant frequency shift.
The problem is I cannot identify the 3 off SOT23 devices in the lower section of the picture (attached), the SO8 is OPA227 op amp, and the overall control is by a HOLTEK HT66F0185 micro.
If the micro is 'bust' then it's a bin job, but if it's just component tolerance/drift/bad design in the controlled oscillator section then I should be able to fix it.
Normally on a non surface mount assembly I could draw out the circuit, but it's a bit small and fiddly on this assembly, especially with the unknown SOT23 devices - which is why I'm after a schematic.

I realise it's a china cheapo but when it works it's OK.

Anyway, thanks for responding and if anyone out there has a copy of the schematic I can hopefully fix it.
Best regards,
timp

[Skippy]

Interesting. It does look to have similarities to the original black Garrett propointer. This could be a good omen, as it may indicate it could work adequately if repaired.

I assume you have a good PP3 battery, kind of obvious starting point. There will be a regulated supply, the SOT89 part, likely +5V. The vibe motor and speaker are probably run from the unregulated supply.
The micro will be OK, I'm sure. The analogue bits are the sensitive area, where trouble could occur.
It's a high-Q oscillator, the amplitude is controlled by a digital pot IC ( U2 ) controlled by the micro. The AC of the oscillator is rectified by a diode to give DC, which is measured by the micro ADC. In the Garrett, the negative peak is measured ( about -4V ), and a potential divider to the regulated +5V is created. The divider output sits just positive of 0V, and goes more positive as the amplitude of the oscillator falls ( when metal is near ).
Garretts have a 'master calibration' button that is used to get the micro to re-adjust the e-pot. Does this pointer have such a button?

Make sure the board is clean. Dirt , flux residue, etc can stop proper oscillation. Also, if water has got to the coil/ferrite rod, you're in trouble, this has to be thoroughly dried out. Water will suppress the oscillation.

This thread on the Garrett may be helpful or not:
Garrett Pro Pointer problem - Geotech Forums

[timp]

Hi Skippy, thanks for the reply.
I think you're right about the digital pot control to set the amplitude, I suspect that the oscillator operation is marginal and probably 'finessed' into working at assembly/test - as hinted at by the bad rework around the tuning caps at the coil end of the board, whereas the rest of the component soldering is good (typical reflow work)..
I'll keep probing the design as a learning process and will report any success on this site.

If anyone else has data it would be useful!