LM394 on my Minelab PCB

[mario]

man is this thing kicking me in the balls!

I doubt It'll ever be the same after I'm done with this. I'm melting the plastic shielding of a lot of wires from all over the board. I just don't have much room to maneuver the soldering iron...

I've removed many resistors from around the oscillator area. I'm finding it difficult soldering those 1/8 watt resistors back without negatively impacting the shape of the sine wave. Its taking me a lot of time through trial and error getting that sine wave back to its proper shape (I have been reinstalling every single resistor I remove until that sine wave starts looking nice. That white gunk on the resistors is having some impact on the soldering ). So far, from the resistors I've replaced, I have yet to find one that will change the frequency.

Also, if you're going to upgrade those darn BYV28-200 diodes, make sure you install them properly (as shown on my diagram)! I might end up replacing many more parts simply because I improperly installed one of them.

I should get all my caps tomorrow, sorry for the lack of updates...

[Mechanic]

Hi Mario,

How long is one full cycle? (start of long tx back to the start of the long tx)

Cheers Mick

[Mechanic]

Hi Mario,

I just had a second look at the scope shots and the frequency is changing with the different caps! Bigger cap = longer tx and longer sample delay and smaller = shorter tx and shorter sample delay. The frequency does look to be about 1.2mhz standard and the frequency with the different cap is about 1mhz. If you can get the sine wave to complete in about 500 to 600ns you should notice a definite improvement in small target response, but ground noise may suffer, but then again the ground you have over there is nothing like the varaible ground here so it may not be a problem.

Now that oscillator I think would be a VCO so if you can change the control voltage by changing some resistor values this may also help control the output frequency. I would start be removing a resistor and measure its value and then put in a small trimmer potentiometer with the original value about midway and then just carefully move it a little bit to see if the frequency changes.

Cheers Mick

[mario]

Hi Mick,

Is it possible to calculate the frequecy from the pictures? or is it best to set up the scope for that?

[Mechanic]

Hi Mario,

It does not look like the frequency is changing at all. You may have to try the 86nf one and see what happens then. Also you may have to try changing resistor values in the area. Use some variable resistors. Make sure you record the value of the original resistors along the way too.

Cheers Mick

[mario]

scope out put of the different caps

No caps, Stock
50mv/Div 2uS/Div x10 settings
Purple trace between caps








Pin 10,IC 4040
.1V/Div 2 uS, 10X


====================================
====================================
5.8nF cap

50mv/Div 2uS/Div x10 settings
Purple trace between caps


Pin 10,IC 4040
.1V/Div 2 uS, 10X


====================================
====================================
14nF cap

50mv/Div 2uS/Div x10 settings
Purple trace between caps





Pin 10,IC 4040
.1V/Div 2 uS, 10X



===================

Hi Mick,

I removed one of those three caps ( the fat green one next to IC 7 ) and installed some resistor pegs to the soldering points. From those pegs I soldered my caps.

Those green, larger caps are adjustable caps, as they are only rated at 1 nF! It is the small purple one (the one next to the other fat cap) that is rated at around 86nF...

Anyways, so much to do so little time...I don't have have caps rated at >15pF, so I am hold up on the order...

Can you help me understand what is going on with my scope readings? I don't think the frequency is changing by much ( just the voltage), by increasing the size of those caps? Am I wrong?


Also, I have thought about it, and you're probably right. I will have to have some one else with the proper station to remove that eeprom. I don't mind at all if it helps me preserve the contents of that IC...The only problem that I see is time, I have so much to get done, and this will come at a later time.

[Mechanic]

Hi Mario,

The best way I can think of to extract the binary would be to remove the 4040 and hookup you address lines from an eeprom programmer there and then also hook up your i/o lines to your programmer to read from. But you will not get the full eeprom this way but you will get enough to revert back to the original timings. To do a full dump you would need to also gain control over the other address lines too. If there were any secrets in there they will be revealed this way and you would also be able to figure out how to access them.

The best way I can think of to remove the eeprom would be using a hot air rework station or an even better way may be to use an infared soldering station. A mobile phone repair place should have one of these and probably places that repair playstations and x-box's too. But I would not recommend you do it because if it fails your detector will be kaput! If you were going to do it however, I would make sure you had all of the timings (i/o pins)figured out so you could replicate them if you had to start from scratch programming a new eeprom. The other thing we don't know is if the addresses are being accessed in their logical order. Someone more cluey on the 4040 may be able to figure that out.


Cheers Mick

[mario]

Maybe just a txt file to re edit and reprogram.

If things were only that easy!

I have not dumped the file just yet, but its not going to be a txt file, its going to be a binary editable with a hex editor. The good thing is that this eeprom has wide adoption so the software to extract it and modify it is not going to be an issue.

The hard part is the actual removal and relocating it. From prior experience, I can attest to the risks involved in the damage to data integrety when handling these eeproms.

[Rov]

Maybe just a txt file to re edit and reprogram.

[Rov]

Is there a dump from the prom! for this yet anywhere,an what format to read?