Author Topic: GFG-8215A Function Generator... No Waveform!!  (Read 492 times)

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Offline stevengendron

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GFG-8215A Function Generator... No Waveform!!
« on: August 05, 2018, 09:34:45 pm »
Hi !
I just bought a function generator. When I turn it on, I can see a dc signal comming up on my scope. If I adjust the amplitude, the DC signal also gets amplified. However, I can't see any waveform.

An interesting fact : When I turn off the unit, I can see the waveform that should have been generated for a fraction of second until the power is completely off.

Before I continue to investigate for several hours, is there anyone who could have encountered the same problem before or could have an idea of what is the problem ?

Thank you for your tips  :)
 

Offline Chris56000

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Re: GFG-8215A Function Generator... No Waveform!!
« Reply #1 on: August 06, 2018, 07:18:33 pm »
Hi!

This kind of fault nearly always indicates a missing power–supply voltage, which may NOT be simply missing from the psu circuits, there may be damaged or open–circuit pcb tracks, burnt–out supply feed resistors, particularly if surface–mount, or even defective op–amps with an output stuck near a supply rail!

Good Will circuit–diagrams are not easy to come by, but open up your gen and write down the type number of all the main devices used in the unit, then look up their datasheets online – the datasheet will indicate where (and what in the case of multi–supply devices like op–amps or Analogue–Digital converters) the power supplies are for each device are.

In a F.G., there's usually +5 for digital control and display functions, and ±12 or ±15V for analogue processing and waveform output.

Have a look round inside and let us know what you find!

Chris Williams
« Last Edit: August 06, 2018, 07:21:14 pm by Chris56000 »
It's an enigma that's what it is!! This thing's not fixed because it doesn't want to be fixed!!
 

Offline stevengendron

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Re: GFG-8215A Function Generator... No Waveform!!
« Reply #2 on: August 06, 2018, 07:22:15 pm »
Thank you ! I'm having my final exams this week so I will take a look next week. I will keep you updated :)
 

Offline stevengendron

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Re: GFG-8215A Function Generator... No Waveform!!
« Reply #3 on: August 08, 2018, 03:02:38 pm »
I finally had some time to take a look at it.
After playing with the knobs, I realized that when the Duty knob was on the adjustable position, the waveforms appeared.
So I opened the generator to take a look at the contacts of the knob switch on normal position.
When i opened it, by looking at the pcb, I could tell that somebody already resoldered the switch before.
I looked at the traces on the pcb and the switch was supposed to make a contact with 2 resistors.
One of the contacts had no continuity when I tested it with my multimeter.
I figured out that the trace on the pcb had probably melted.
So I soldered a wire between the switch and the resistor.
I works fine now. :)

 


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