bounty huner 840 died today is there any common faults

[Dean1971]

Hello everyone can anyone help with where the test points are or any common faults?
went out detecting today I thought I take my bounty hunter 840 but after 20 minutes it died on any ideas please?
Regards dean

[geoscash1]

schematic

Don't know if this helps much but here is the schematic. maybe someone with knowledge of this can edit the schematic and put test points on it for you,

[homefire]

Dead Bug ? Define Died ? No indications of life what so ever ?

I know sounds stupid but did you try new batteries ?

Check obvious stuff. Battery Connector. Battery Wires.

[Dean1971]

Hello geoscash1 thank you schematic.i hope someone will give me test points or where to look for faults
regards dean

[Dean1971]

Hello homefire thank you I have check all the easy stuff. I'm get some power on pcb and the battery test work on the meter for both battery's
I just don't know weather it's a problem with the amp because there no sound. But not 100%
regards dean

[Tim]

What about the speaker?. My vlf-spd had a faulty speaker, but worked on headphones. Tried phones?

[Dean1971]

Hello Tim tried head phones still nothing . If I know where the fault is I can fix it but I am only learning about electronics and love doing it not has experienced as a lot the guys on here. This detector has fund me a lot of stuf in the past and I don't want to part with it so I
want fix it and learn from it also.thank you Tim
regards dean

[kt315]

Dean..... try this. i answered on tesoro faulty but its your case too... connect according this diagram...
you have to get a sound... if not sound... you have to search only sound part. if yes...
search left part...

(do not take attention on red lines...)

[geoscash1]

Here are some points of interest

Hello geoscash1 thank you schematic.i hope someone will give me test points or where to look for faults
regards dean

Well, I can give this a shot but my knowledge is lacking as well but some of the places on the board have specific points of interest, some of the gurus here can correct me if they see an error. It looks like it uses an operational amplifier to amplify the signal so you can check the outputs, it also uses a comparator LM393 for differntiating voltages or for the disciminating portion of the circuit.

First thing I'd check since the easy stuff is already known (batteries good, power to board etc) is to un plug the coil and check it, it may have a broken wire in the cable as it is an older model, I am not exactly sure how you would test this particular coil but someone here should be able to tell you.

The other important places are the op amp and other Ic's and switches on the board. I dont know what battery/batteries yours runs on (this schematic shows two 9v batts) so you will need to find out what the operating voltages should be.

Here is the op amp - LM358
Check pin 8 for input voltage
Check the output pins - if you have a scope you should see a signal or some sort of wave form


Here is the Comparator - LM393
check pin 8 for input voltage
Check the outputs on pin 1 and pin 7 (not sure what to look for as far as voltage differences)


Here are those spots plus a few others to check on the main drawing


Hope this helps a bit and surely, someone here has more experience with the older vlf circuits and should be able to help out.

NOTE - looks like kt315 posted before I was finished posting so I would recommend following his advice...

[homefire]

The MPS-A13 is commonly used in the audio for many machines. I've had to replace like three in Garrett Machines that failed for no apparent reasons.

I would check that . Then as stated check power to all IC's if good follow the audio back from Speaker until break is located. Being a older machine it could just be a dried out Electrolytic Cap that dried out.

[Dean1971]

Hello kt thank you I'm going to try a few more things if that I will your circuit for sure
regards dean

[Dean1971]

Hello homefire I have check all transistor all ok just not sure about ics
the caps was first thing I check after battery and switches power to pcb
thank you
regards dean

[Dean1971]

Hello geoscash1 thank you I have check all transistors just ics I don't know how check I'm sure if post the results some of great people on here will tell me if something wrong with them thank you
regards Dean

[Dean1971]

Hello geoscash1 thank you this is my results on my checks + _ = 15.00 volts (lm 358 pin8= 15.00 pin7 4.81) (lm392 pin 8= 14.99 pin7 4.17 but I don't know if this is good or bad ?
if any of the kind gentlemen on here can tell me
thanks everyone
and geoscash1 + kt +Tim+ homefire and anyone else I may have forgot regards dean

[Dean1971]

Thank you everyone I have got my bounty hunter 840 going. I replaced the two ic's and works as good as new
i put two ic's sockets in case it ever happens again I think it was just the conpariter ic but I had decided to put sockets on the pcb.
I replaced them both ic's
thanks
regards dean