Instek FG-8050 Function Generator Repair

Hey guys,

I've got an Instek FG-8050 Function Gen that I was given awhile ago. It produces an output, but at full amplitude, the output is only ~2v p-p. Upon inspection, R474 on the bottom board, right near the output connector, is black and charred beyond recognition.

Does anyone have a service manual for this thing? There's nothing on Google. Worst case scenario I will have to reverse-engineer a schematic of the section that blew.

You are right about the google search.

ParkingLotLust said:

Worst case scenario I will have to reverse-engineer a schematic of the section that blew.

Click to expand...

Sounds like the best plan, especially if the only problem is P-P values (i.e., correct signal except for amplitude.

My guess is that the output impedance of the sig gen is controlled by that resistor (probably 600Ω or 50Ω). That being the case, someone may have attached the output to a high voltage/current circuit and fried it.

Right off, after determining that the burnt resistor is, in fact, part of the output circuit, I'd start by replacing it with a high (say 1MΩ) value resistor and work your way down in resistance until you get the full P-P value listed. If you have a way to check the output impedance, I'd do that as well.

Also, check the physical size of that resistor and use replacements of equal or greater dimensions.