4900/5900 modification

[scrungy_doolittle]

The 4900Di pro has a fixed volume control. I tried replacing it with a 50K pot, but it doesn't give much control.
Does anyone have a schematic for the 5900 that would give the pot value? And just removing the jumper wire that connects the ends of the pot location
on the board, essentially making the pot into a single wire may not be enough.

[scrungy_doolittle]

pot value

The pot value is 100K.
Additionally, you can make the sensitivity mod to the 5900 and 6000 as follows:
The sensitivity control on the 4900 controls the current through the coil. This bit of the circuit on all of the detectors is essentially the same. The oscillator signal is divided by a 4024 and on pin 11 of that chip, the drive signal comes out to the transistor. there is a 2.7k resistor in series (but what I have found in actuality, is that the built boards have a 4.7k. This doesn't make any difference. The base of the transistor is tied with a 4.3 volt zener diode to the positive rail. This means that the base is for all practical purposes locked to 4.3v. There is a resistor from the emitter of the transistor to the end of the didoe that ties to the + supply. This resistor controls the current through the transistor, by virtue of the base voltage being locked at 4.3 volts. on some schematics, this is listed as 68.1, on others it is 150. on the 4900 it is 150. the sensitivity control, simply lifts this resistor on one end (R80 in the 4900 and R11 in the 6000 and R24 I think, ion the 5900. ) and ties it to the center pin on a 5K pot. The outer pin on the 5K pot then ties back to where the end was lifted from, resulting in the 5K being in series. The end of the pot used, is such that when the pot if fully clockswise, it's resistance is 0. This puts the 150 ohm resistor in , maximizing the current, and driving the coil maximally. When turned to low sensitivity (the left end of the pot), you now have 5K+150, so the current is really less, and the signal does not penetrate as deeply. This reduces the depth, but is important when working through high mineralization, looking for ore. The mod is trivial to make on the 5900, and indeed can be made on all of the instruments. One objective has been achieved. Next I am looking at installing sigbal as a modification to the 5900Di pro. That looks to be an extra amp, and indeed the 5900 schematic has it as a daughter card. It has been integrated in the 6000s. I don't seem to have it on my 5900.

[Silver Dollar]

That sensitivity control sounds good! Many just adjust a threshold and it doesn't really do much.

[kt315]

mr bill mods he shared. can you give pics inside and outside of your 4900?

[scrungy_doolittle]

I will be glad to as soon as I get back in town. Will be gone all next week. The first mod you posted, is essentially what I am discussing. He replaced the 68 ohm with a 51 ohm. Whites usually uses a 120 ohm. The 4900 to the resistor (R80) which was a 120 and put a 5K pot in series with it. When the pot os turned fully clockwise, the resistence is 120 and at maximum sensitivity. I would guess that one could use a 51 ohm resistor in series with a 5K pot.

[Mrand]

The enlargement TX power does not cause the special heigh of range. It can however cause pretty big troubles in the difficult ground. Here is necessary compromise. Better solution is the regulation of sensitivity and change her depending on the ground.

[kt315]

can you give pics inside and outside of your 4900?

[scrungy_doolittle]

can you give pics inside and outside of your 4900?

as I said before I will be glad to as soon as I get back in town. Will be gone all next week. The first mod you posted, is essentially what I am discussing. He replaced the 68 ohm with a 51 ohm. Whites usually uses a 120 ohm. The 4900 to the resistor (R80) which was a 120 and put a 5K pot in series with it. When the pot os turned fully clockwise, the resistence is 120 and at maximum sensitivity. I would guess that one could use a 51 ohm resistor in series with a 5K pot.

[n0xes]

I'm curious if you ever posted the photos of the inside of your 4900? I have a 4900 DL max im trying to revive and do some mods/upgrades to.