I am led to believe that this transistor came out of a (bass) woofer - one one speaker, and only one transistor (not two).

This is the best photo I can get:


The markings appear to read

MCCO - 0031

Googling L70M09CV comes up with nothing related.

Any idea what it is, a datasheet, and/or a suitable alternative?

I don't have a photo of the PCB, as it belongs to a Thai friend, who speaks no English, and my Thai isn't fluent, so more details are either sketchy or non-existant. I may be able to get a photo of the PCB tomorrow.

FWIW, I get 0.6V across the collector-base and emitter-base junctions, when forward biased - when checking it and assuming it is an NPN transistor.


It's most likely an L78M09 9V, 500mA linear voltage regulator. You may replace it by an 7809 or 78S09 if those are easier to purchase at your place.

  • \$\begingroup\$ Ah, the second number is an 8 not 0... well spotted. Many thanks. I thought I might have been a regulator and did ask my friend if it was from the power supply part of the circuit but they said no... but then he said a lot of stuff that I didn't understand :-). \$\endgroup\$ – Greenonline Nov 22 '18 at 3:22
  • \$\begingroup\$ As an update - I ordered some 7809 regulators for my Thai friend off eBay, and after a short delay they arrived yesterday. He has replaced the regulator (along with a couple of dodgy electrolytic caps) and he told me today with a big grin that it works. Many thanks for the component identification, you really made someone's day :-) \$\endgroup\$ – Greenonline Dec 16 '18 at 17:34
  • \$\begingroup\$ You're welcome. \$\endgroup\$ – Janka Dec 16 '18 at 18:49

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.