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Title: Help with transistors
Post by: Den. on April 26, 2026, 04:28:17 PM

Hi... I'm looking at a Bose L1 model II PA amplifier and I'm looking for help in interpreting a series of voltage measurements. There's a pair of what I think are transistors that look suspicious. On the diode mode these are the readings I got. Can someone help me? Thanks.DSCN2636.JPGDSCN2638.JPG

Title: Re: Help with transistors
Post by: galaxiex on April 26, 2026, 08:08:46 PM

Those look like voltage regulators.

Clean the schmoo off the top where the "L78" number is so we can read it.
That is likely the part number.

Title: Re: Help with transistors
Post by: Tassieviking on April 28, 2026, 07:29:01 AM

U115 Volt Regulator -15V L7915CD2T D2PAK ST
U116 Volt Regulator +15V L7815ACD2T D2PAK ST

Service Manual:
https://studylib.net/doc/27942375/l1-model-ii-service-manual?p=32

Title: Re: Help with transistors
Post by: Den. on April 28, 2026, 07:05:02 PM

Quote from: Tassieviking on April 28, 2026, 07:29:01 AMU115 Volt Regulator -15V L7915CD2T D2PAK ST
U116 Volt Regulator +15V L7815ACD2T D2PAK ST

Service Manual:
https://studylib.net/doc/27942375/l1-model-ii-service-manual?p=32

Thanks for the service manual, this will be very helpful. Den

Title: Re: Help with transistors
Post by: joecool85 on May 01, 2026, 09:17:39 AM

Quote from: Den. on April 28, 2026, 07:05:02 PMThanks for the service manual, this will be very helpful. Den

And thank you, Den, for the detailed photos and testing information - this makes it a WHOLE lot easier to known what you are looking for.

Good luck in the repair!

Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Solid State Amplifiers => Amplifier Discussion => Topic started by: Den. on April 26, 2026, 04:28:17 PM