A tester for LM13700 and CA3080

These IC are used in a lot of vintage and pro audio equipment. They are also prone to failure. This simple tester uses a VCO circuit and a small speaker. Simply plug in the suspect IC into the socket and 'twiddle the knob'. If the OTA is good/genuine you will hear a frequency sweep on the small speaker.

There are two DIL sockets for the LM13700. This is because this is a dual OTA, you can plug the IC into both sockets to test each side of the LM13700. Only insert one IC into the tester at a time. You can also insert a SOIC to DIL 16 or 8 pin adapter and the the tester for SMD devices. I have tested it with CA3080 SMD variants such as TA3080 and SA3080 and it will also test these devices.

Note about RV1. The value is not critical. I used a 100K linear potentiometer. If you find the tester does not oscillate with a known good IC, then disconnect the leg of the potentiometer that connects to +15V (the left hand side of the potentiometer when looking at the PCB wth the speaker at the bottom). On the prototype version I left this side of the potentiometer disconnected and it functioned correctly.

If you do not have the MPSA14 NPN Darlington Transistor you can substitute if for a similar device. I used the BC817 which worked well but I needed to fit the transistor the opposite way round due to the different pinout.

Find this project on my Youtube channel https://www.youtube.com/watch?v=CrTq0XjvPdc