4900/5900 D board and schematic

[kt315]

can you give pics inside and outside of your 4900?

[scrungy_doolittle]

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.

[Altra]

I found one labeled meter which might just be the meter PCB?
It was in a directory labeled 6000 so might not be the right one....

[ATTACH]31128[/ATTACH]

Just for reference that drawing came from this patent. DI6000 is mentioned in the citation

http://www.google.com/patents/US4783630

[scrungy_doolittle]

I think there is more to the meter circuit. looking at the 5900 schematic, and a board, it appears that ic's numbered 200 are all on the daughter card.

[Silver Dollar]

I found one labeled meter which might just be the meter PCB?
It was in a directory labeled 6000 so might not be the right one....

[scrungy_doolittle]

Thanks, Silver Dollar! I downloaded it. This is going to be a huge help. Now I just have to find a 4900. I have the 5900di pro (but not the SL, which I understand is just the 5900 in a new case.)
I have compared it to the 6000 schematic. Quite a bit of difference. Even in the audio. For example, I can't find the volume control on the 5900 schematic. They did not use the same audio circuit. Seems like that should have just been a jelly bean dropin.... This schematic is a bit clearer than the 6000 schematic. Gives more information. It is for board 505-0162. my 5900 is 505-0129, so this is quite a few boards later 1989 board number.

The detector picked up as non working off ebay, just has a bad battery case. Connect 6v and it works just fine on the bench.

Cheers
Woody

[scrungy_doolittle]

can't see it. Can you zip it?
click on it and it gives an error

[scrungy_doolittle]

Well to answer some of my questions: the 5900 uses board 505-0129-3 1985. It has a large daughter card for the VDI functions, with a set of pins to connect it to the main board.
The 4900 uses 505-0132 1985. The volume pot measures about 87.k ohms on the 5900, so it is almost certainly a 100K. Which is why my 50K doesn't work on the 4900. I have not removed the boards from the housing to compare the top sides. When I do however, I should be able to get a better feel for differences.

So what I need is the schematic for 505-0132 and the one for 505-0129.
The 4900 has a sensitivity pot, and the 5900 doesn't. The 5900 has a sigbal pot. I am wondering if they are the same thing, just with different names. I plan to trace those two items out.

[Silver Dollar]

I have this for the 5900 Di Pro SL;


It looks like the 6000...

Oops can you see the pic? I cannot convert it to JPG to show as it's too big then...

[scrungy_doolittle]

I just snagged a 5900Di pro off ebay, not working or for parts 100.00 total. The guy says it doesn't power up. I have a good 4900Di pro. I have not gotten the 5900 yet, but I suspect that these will have the same board. Does anyone know (Karl?) I will be looking at the board in the 5900 as soon as it comes.

Given the design of the battery connector on the 4900, I'm betting that the 5900 battery connector is just not snugging up to the spring loaded contacts, and that
simply fixing that will fix the 5900, (the foam block on the battery compartment case might be gone) but if It doesn't, I'm going to have to try to repair it. My 4900
was missing the battery pack, so I made one, and used a pair of wires with a plug on it to connect the power to the 4900, and it works as well as a 4900 can possibly work.

I've picked up most of the schematics off the board, but while at least one claims to be a 5900, it appears that it really is a 6000.

Reading the 4900 Di pro manual, in the introduction by "Sierra", he states that Whites created the 4900 by removing the volume control from the 5900, and eliminating the meter circuit, and adding the 10 turn stacked manual ground balance pot.

Looking at the circuit board, you can see where the volume control was shorted out with a wire (which I have removed, and tried to install an external pot for volume control (which is not working quite right, it is a 50K). Looking at the schematic of what claims to be a 5900, it looks like the volume control is a 250 ohm. That doesn't make a lot of sense. You can also clearly see where the meter circuit was unpopulated

Additionally, on the 4900 board, there is a big honking coil that doesn't appear in what claims to be a 5900 schematic.
So:

I would like an official schematic for the 4900Dipro, and the 5900 Di pro.

Does anyone have one?
Cheers
Woody