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Draco's GS 5 problem

Reg

New member
Hi Draco,

I started a new thread so it doesn't get more confusing.

Now, I apologize for my error in determining the problem. I completely missed a very important voltage reading you posted on the last op amp, the TLC2262. That voltage reading is the +5V you should have on pin 8. You measured 2.38v which is wrong. This indicates a power supply problem that has to be evaluated. So, now we have to deal with the wrong voltage and find out why it is happening.

There are a couple of reasons the +5V could be low. One reason is there is a part that is bad causing the voltage to be drawn down. The other is something is wrong in the +5V supply. If it is the supply, then the most common part to go bad is one of the capacitors, probably one of the two used in the voltage doubler stage.

So, now we need to determine just what might be wrong.

To begin with, we need to find the +5 Volt supply.

So, to begin with, we need to find the +5V supply to take a few measurements. We will be looking for VR3. Now, if you set the GS 5 up so the TL062 is in the lower left hand corner, then the VR3 will be closer to the upper right hand corner of the pc board. You will also want to look for D1 and D2 in that general area close to the VR3. There will also be two capacitors, maybe listed as C 15 and C17. These capacitors are part of the doubler stage.

Now, the +5V regulator is VR3 which is a LP2950-5 IC. The IC has 3 legs. The center leg is ground, so any ground will work to connect the black lead of the digital voltmeter. Now measure the other two legs. One should be +5V and the other should be over 10V or so. Let me know what the legs read.

Reg
 

draco

Member
Hi Reg

I guess the LP 2950 is the one marked with the red circle. (I can not read well)

I just measured voltages
and indicates that in the photos below.
 

Reg

New member
Hi Draco,

The LP2950 is located up from the TL2262. I have circled the IC. Check the voltages on the 3 pin IC inside the white circle.

Reg
 

draco

Member
Sorry Reg, online translator sometimes does not give me the correct translation.


 

Reg

New member
Sorry, it was my mistake. I said the LP2950 was in the upper right hand corner but meant to say it was in the upper left hand corner.

The LP2950 (or could be a lp 7805) requires a 9+voltage at the input but doesn't appear to have that. Located just to the right of the LP2950 are two diodes, D1 and D2. Check the voltage on the cathode of D1 and then the voltage of the cathode of D2.

Also, look the board over very carefully around the two capacitors, C15 and C17. See if one or more of them is bulging and/or leaking.

Reg
 

draco

Member
Hi Reg.

I've looked and all capacitors seem fine.

I can not measure the voltage of the diodes, because I have no space to the ends of the tester. Would have to remove the board and is complicated for me ...:stars:
 

Reg

New member
The two diodes are open enough you should be able to connect a meter to the cathodes which are the ends that have the line on them. The rectangular block has the diodes in the picture.

Either the power supply is bad or maybe one of the IC's are bad and loading down the power supply. Checking the power supply should be the next check but you can see if you have one IC that is running really hot. Don't check the power FET or any of the power resistors because they will be hot and also have high voltage. Just check the various 8, 14, and 16 pin chips.

Reg
 

draco

Member
Hi Reg.

There is no space between the pcb and diodes. I can not put the ends of the tester. Impossible, no space.

Thank you.
 

draco

Member
Oh, sorry Reg, I did not understand the question.
Confused capacitors with diodes.

The diodes give a reading of -245 with GS5 on.
and 208 with GS5 off
 

Reg

New member
Hi Draco,

There can be a couple of things wrong. First one or more of the capacitors in the +5v supply might be bad. The probably could be checked with a capacitor checker in place. I haven't tried this yet, though.

Another problem could be another capacitor connected to the +5V supply through a low value resistor like the ones near the NE5534 or AD8055 could be bad. Another possibility might be a bad IC that uses the +5V supply. If you have a heat sensor gun, you might look for an IC that is running hotter than the rest and try changing it. There is a slim possibility you could test for heat with a finger but that doesn't work that well.

If the problem isn't an IC then you will have to find someone who will fix the pc board for you.

Remember, you can find a schematic of the GS 5 on the Geotech forum. Search for GS V or GS5 schematic and you should be able to look at a pdf file that is quite accurate. Here is a link to the Geotech forum. Just drop down to the GS V and click on the paperclip to look at the attachments.

http://www.geotech1.com/forums/search.php?searchid=178988

Reg
 

draco

Member
Reg thank you very much, at least we tried. I will keep GS5, until you find someone who wants to fix it.

Greeting
 

Reg

New member
Hi Draco,

I haven't given up yet. If you get time, check to see if either of the two Tantalum 10 uf capacitors near the NE5534A at the front of the board are warm or hot. Tantalum's have been known to go bad if not used. If one is much warmer than the other, you can gamble and cut it loose on one leg but if you decide to do this, cut the leads leaving as much as possible of the lead on the top of the board so you can solder another capacitor to the leads. In other words, cut it in the capacitor or as close as possible to the capacitor to leave as much lead as possible. This will allow you to replace the part without removing the pc board which is a real pain to do. The capacitors are usually sort of round and possibly yellow or orange in color.

There are other Tantalum capacitors that can be checked. I like using a heat gun I purchased off ebay for about $25.

Do you have a capacitor checker on your digital voltmeter? If so, you can test the capacitors with them also. In fact, you can check capacitors with an ohm meter by looking for a low ohm reading. I am not sure about your ohm meter so check with the leads each way, meaning red lead on + leg and then black lead on + leg. Tantalum's don't like reverse voltage and can read low one way. If it reads low both ways and is a little warmer than the others then you might gamble and change it.

Reg
 

draco

Member
Thanks Reg, I'll try again.

This is my tester, but I also have a digital meter tempetatura.

If the tester used, please tell me how I use it. This will also learn.

Thank you.
 

draco

Member
My old goldscan5 has come back to life. a problem with a capacitor motherboard.
 

Idefix

New member
Hello Draco.

I see in the old posts that someone had sent you in the past the schematics of the Goldscan5
As it is not manufactured today, , and very hard to find documents, would you agree to send me the files you have of the Goldscan 5
I can give you my adress if you are OK.

Many thanks.

Best regards
 
Hello, sorry to bother, i'm also interested in the gs5 schematic. If is possible, my email address is: ionut_mtb@yahoo.com
If not, i understand your decision. Thank you anyway!
Jonny
 

Idefix

New member
Hello Draco.
Thanks for your help. My mail , (replace [arrobas] and [dot] with the good values. )

idefix3582[arrobas]free[dot]fr

Looking forward to read you .
Thanks again.
 
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