Successfully repaired an instek FG-8015G

[Ferroto]

So awhile ago I purchased a used function gen from ebay. It was sold from a seller that said he got it with a bunch of instruments labeled as nonworking or defective it had a big old sticker on it saying défectueux (defective) but it was 30 bucks and located in Canada so I figured I'd take a crack at repairing it.

When I got it home I turned it on and nothing at the output however the pulse output still worked. so i took the cover off. I discovered that the board was worked on by someone else. It was easy to see where because the rest of the board was wave soldered.

Bodge City!! I especially like that resistor on stilts. You can probably smell those resistors through the internet to. I was the one who removed Q506 srry I don't have any pictures from before I started working on it.


Both Q506 and Q505 were getting hot up to round 90deg Celsius. So I decided to desolder them both and test them out of circuit Q505 was shorted internally fellas.


Now according to the datasheet the Q506 was supposed to be a 2n2905 (NPN) and Q505 was supposed to be a 2n2219 (PNP) and both are wired up in a class AB type configuration and are the final amplifier stage before the output. However when I hammered the heatsinks off both I made a shocking discovery. They were both 2n2219's they also both had fresh solder on them which means they were replaced by the previous owner.

So I replaced both transistors, reused the heatsinks, adjusted the voltage rails (I was messing with the voltage adjust trying to correct a voltage drop caused by a shorted transistor.) and now it works perfectly.

Here's the schematic for those interested.

[mij59]

The unit is quite old, you might want to check the filter caps C101 and C103, in my GFG 8015G they only lasted  25 years.

[Eng_hassan85]

Good Work .. Keep it up

[preludelinux]

Sure can smell the burnt components. good job with the fix and finding the other persons mistake. i wonder what happened to cause the last person to repair the unit like that. usually i always get a bad feeling once i find out someone has tried.

[Ferroto]

Sure can smell the burnt components. good job with the fix and finding the other persons mistake. i wonder what happened to cause the last person to repair the unit like that. usually i always get a bad feeling once i find out someone has tried.

Best I can figure is voltage was fed into the output terminals. two of the resistors fried were 1/2 watt 100 ohm's in parallel at the output for 1 watt 50 ohm effectively.