Kevin's BlogCheap ICL8038 Signal Generator Repair
I have a couple of those very cheap ICL8038 based signal generators available in PCB kit format from overseas cheap electronics suppliers. They are usually available in two options: with or without a laser cut acrylic case.
They generally work ok for the kinds of things I need and typically have:
- Four frequency ranges between 5Hz and 400kHz.
- Frequency, Duty, Offset and Amplitude controls.
- Square, Triangle or Sine wave output.
- 12V supply.
They are based around the ICL8038 waveform generator IC, available in 14 pin DIP format. The kits tend to be cheap, all through-hole components, and for simple applications it works well.
Until you accidentally feed it a reversed 12V supply, in my case from a centre-negative 12V barrel jack, by mistake. Then it goes pop and stops working.
Diagnosing the Issue
To be honest, it was pretty easy to see what had gone wrong…
A close look at U2 (bottom left) and I can immediately see the source of the literal “pop” I heard. This is a 78L09 regulator, so no wonder it didn’t like a reverse polarity supply. But what else might have gone with it?
These things come with pretty sparse instructions, but they do come with a schematic:
From this, I can see that the ICL8038 is supplied by the 12V line directly, along with the regulator. The other thing that would probably get upset by a reverse voltage is the 100uF capacitor C10 on the power input. The other two ICs are supplied by 9V which comes from the regulator, so there is a good chance they survived.
At this point I did wonder about getting some components and fixing it, but they are so cheap to buy, that I thought I’d just buy a new PCB-only kit, allowing me to reuse the acrylic case that came with my original kit. So that is what I did.
The First Issue
The replacement, PCB only, board is the black one on the left. But it is slightly longer than the original and the pots are spread out slightly more. Also the jumpers are in different positions, so this all means I can’t reuse the same case!
But at least now I had a new working module which allowed me to test the three ICs. The TC7660S and TL082 were both fine, as I thought they might – being fed from 9V after the regulator. But the ICL8038 was indeed dead.
So at this point I decided to repair the original PCB. This means replacing the 78L09, and just to be sure, the 100uF capacitor too on the original board so I can use it with my case.
It will need to use the ICL8038 from the new kit too.
The Second Issue
So, the 100uF capacitor I had was slightly too tall for the case!
On closer inspection, these kits use a particularly short and dumpy 100uF, 16V capacitor. I didn’t have any of those for 100uF, but I did have one for 220uF so I’ve used that instead.
Conclusion
It is just so typical of these overseas sites that “PCB without case” turns out to be a slightly different PCB to the PCB that comes with a case!? Oh well.
I now have a decision – do I buy some ICL8038 chips rather than pinch one out of another kit? Really, I was after repairing my encased version, but now it seems wasteful to have a full PCB ready to go for want of a single, pretty cheap, device.
I could always design and build a replacement case for the case-less version I guess…
Kevin
dr 🛠️🛰️📡🎧