The EICO 150 Solid State Signal Tracer redux, part two: Measurements.
Monday, May 18, 2026 at 09:44:02
The EICO 150 that was on the bench had a bad speaker. Now it has noise. Lots and lots of noise.
I’m going to put a scope on the transistors to see what they look like, in particular Q3 and Q4, the output pair. This is with minimal gain, no input signal. The test is trying to determine where the noise is coming from. I made a partial determination earlier with a suggested test - unhook the base of Q4 from the circuit. If the noise stays, it’s Q4. If it goes away, it’s back further in the circuit. It went away, so something further back is bad. I’m also going to measure the voltages on each transistor for reference.
There’s a short video on the testing I did, you can view that here: https://www.youtube. … /watch?v=rtbDVdCnb3k
Q3
Base
Emitter
Collector (Output)
Some noise there on the collector. This will also appear on the base of Q4 since they are direct-connect.
Q4
Base
Emitter
Collector (Output)
The signal is being amplified by the output transistor. Perhaps this explains the current draw? The output transistor is doing something instead of being in it’s no output state. What’s causing this? Maybe Q3 is just noisy. Maybe one of those carbon composition resistors is noisy. It’s going to take some more work to make that determination.
Voltages
Measured:
Manual says:
You can see there are some variations here. Further work is needed.
Stay tuned!
References
The entire EICO 150 YouTube Playlist: https://www.youtube. … yAcib71v-995pS_-4jDr
Next part of this series: Coming soon.
Previous part of this series: https://wereboar.com … -tracer-redux-noise/
Final thoughts and wrapup: Coming soon.