Function Generator Repair

Several years ago now I purchased a cheap open PCB style “Function Generator”. Even though it was cheap it seemed more logical then building one from scratch. I remember doing that way back when I was in my early 20’s!

More recently I have been attempting to repair a Hameg 203-6 and the only safe signal to had was the units calibrated square wave. As the Oscilloscope appears to be modulating it would have been nice to have a separate wave form generator. I do have another Hameg but space on my desk is limited.

I recalled having this function generator but suspected I had chucked it in the spare parts bin when it failed.

I fished it out and supplied it with 6V. This value was chosen as I spotted it has a 78L05. The LCD proved to be faulty as did the main PCB.

I have another LCD that will do the job on order form “Aliexpress” but that could be months arriving. So I disassembled the LCD cleaned the tracks with some isopropyl alcohol and reassembled the display. This reassembly proved quite difficult, but I did eventually get a usable LCD.

Pocking around with a meter and a scope seemed to indicate that the microprocessor was still working. The LCD confirmed that it was at least talking to that.

There are 2 other IC’s on th PCB. The first is a surface mount dual low noise op amp (NE5532) and the other is a socket mounted thru-hole super voltage converter (ICL7660S). It was far more likely that the voltage converter was faulty and possibly even expected to fail, if the socket mount was anything to go by.

As the parts were coming from China, I ordered a quantity of each. They arrived in due course and I slotted in the ICL7660S to restore operation.

I still do not have a dedicated power supply or a case for this unit so it might become a project to make it into a bench instrument as I have a supply of spares should I blow it up!

Posted in Fixes and Bodges, Projects, Work Bench

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