White's PI3000 re-build

[dbanner]

the original coil is orange and looks different : https://www.youtube.com/watch?v=q951...RlY3RvciB0ZXN0

Yet the schematic for PI1000 shows notes giving 11inches dia. 18 turns for the coil which works out to around 300uH (0.4mm wire)

[kt315]

It might be the coil.

The clock is 30kHz. It looks like the PRF is 3kHz? With a pulse width of 30uS. Time to first sample is 30uS after end of Tx pulse. Time to second sample is 270uS after end of Tx pulse. All pulse widths are 30uS in duration.

In the notes on the first post, the original coil was opened and found to have 36 turns @ 11 inch diameter which works out to app. 1200uH.

The 950 coil is around 300uH????.

Put in a higher power rated resistor for R16.

it is maybe second concept of Eric. late concept he did. MAY BE, i do not sure know here fo the 3000. yes, then, 1mH coil, high TX frequency, a resistor in circuit of coil is 30+Ohm. we say '1mH coil PI detector'.

[dbanner]

In the sim I use plus and minus 5V. The actual circuit uses VDD +5 and VSS -3.5

[dbanner]

I see clock inhibit(pin 13) is tied to Vss (set to low) on schematic. This pin must be set to low to allow clock to count normally. If there is a problem with the power supply, you need to check the voltages on the power rails of the PCB as well.

[dbanner]

It might be the coil.

The clock is 30kHz. It looks like the PRF is 3kHz? With a pulse width of 30uS. Time to first sample is 30uS after end of Tx pulse. Time to second sample is 270uS after end of Tx pulse. All pulse widths are 30uS in duration.

In the notes on the first post, the original coil was opened and found to have 36 turns @ 11 inch diameter which works out to app. 1200uH.

The 950 coil is around 300uH????.

Put in a higher power rated resistor for R16.

[Carl-NC]

R16 has nothing to do with the charge pump. 3 possibilities:

1. The TX pulse is too wide or the TX timing is not working
2. There is a dead short in the search coil
3. R16 power is rated too low

From the photo R16 does not look like a 1W resistor, more like a 1/2W or maybe even 1/4W. I would need to know the TX pulse timing to figure out what it needs to be. If you replace it, try running the circuit without the search coil attached to see if the TX pulse is working correctly.

[Lucar]

Hi,

I'm Luca , the author of the posts You resumed from Findmall if I recall; I don't remember anything about that, it was a long time ago, but I still have the PI 3000 somewhere in my house and one thing for sure is that the 950 coil is not the original one. As far as I remember the original coil was not shielded and that was a damned noisy detector. Anyway adding a pic16F did allow for flexible timings programming.

Cheers
Luca

[Octopulse]

you have not a pulse signal in TP6 (test point 6). Q3 is constantly open. Q4 is too. R16 burn.

I don't have any test equipment to check that....just my humble MM.

Thanks.

[Octopulse]

Have you checked Q4? Maybe this is faulty too.

Diode test for a PNP transistor.....about 0.45v and 0.55v between emitter and collector.

Q4 might be a problem. I'm not sure what has lead to the R16 burnout as I am keeping to the exact stock specifications except for the voltage pump IC but that shouldn't cause a problem.

Thanks.

[kt315]

can I simply change the resistor value and if so, what is recommended

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just on a time of the repair. after it you have to be back the resistor to its original value.

[kt315]

you have not a pulse signal in TP6 (test point 6). Q3 is constantly open. Q4 is too. R16 burn.

[Octopulse]

D5, D6?

All diodes across the board are good.

[GeoMax]

Have you checked Q4? Maybe this is faulty too.

[daluka]

D5, D6?

[Octopulse]

Well everything was going fine as far as 6 caps, 1 IC charge pump and one diode replacement was concerned.......shortly after powering on, R16 let out some smoke !!

Is the upgraded (to 12V) charge pump IC responsible.....everything else is to original specifications. Both the 6 x 1.5v AA pack and 8 x 1.2V NiMh gave the same smoking resistor.

R16 is 5.6 Ohm / 1 Watt (off the spec sheet).............can I simply change the resistor value and if so, what is recommended. Any other considerations?

The picture shows the R16 with it's new burnt look....coil pins directly above (coil has been removed).

Thanks for any help.
Tony