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Uncle Bulgaria · 20th Jul 2019, 2:06 pm

Interpretations please!

I've jury-rigged a headphone-out to three crocodile clips and used this to put a 1kHz sine wave into where the tape heads meet the motherboard (tape heads disconnected).

The sine wave is 0.5V.

At the collector of the first transistor in the path (T301 - labelled in the diagram as a BC 384 BS, but on the board both channels have a BC 550B) is the waveform shown, approx. 1.5V total amplitude.

At the emitter is the form shown; ~20mV.

Call me wet behind the ears, but shouldn't the wave in be amplified as the wave out?

20th Jul 2019, 2:06 pm	#10
Uncle Bulgaria Nonode Join Date: May 2016 Location: Cornwall, UK. Posts: 2,339	Re: Uher CR240 Troubleshooting Best Practice Interpretations please! I've jury-rigged a headphone-out to three crocodile clips and used this to put a 1kHz sine wave into where the tape heads meet the motherboard (tape heads disconnected). The sine wave is 0.5V. At the collector of the first transistor in the path (T301 - labelled in the diagram as a BC 384 BS, but on the board both channels have a BC 550B) is the waveform shown, approx. 1.5V total amplitude. At the emitter is the form shown; ~20mV. Call me wet behind the ears, but shouldn't the wave in be amplified as the wave out? Attached Thumbnails