The EICO 150 Solid State Signal Tracer redux, part 5: Mistakes were fixed.
Monday, June 1, 2026 at 07:25:24
In the last part of this series, I put some new transistors in the device. And had to replace them once again because they were inserted incorrectly.
With that being fixed, it’s now time to check the unit for actual operation, make one final mod, and see what we have. Here’s the data:
What the manual says:
What the old transistors said:
What the new transistors said:
And finally, the noise levels:
The noise is very similar to what we saw after Q3/Q4 replacement, so the previous transistors, while providing the noise, don’t seem to be causing it. Some commentors on the youtube videos suggested the resistors are probably doing it, and I tend to agree. Old carbons are noisy.
The transistors also show some improvement in voltages, especially Q1 and Q4. Q1 should be off when measured in this configuration, and it is. Q4 is now closer to the Vdd rail, as it should be. Current draw on Q4 has also reduced, but is still high - probably because it’s amplifying noise. We’ll see what resistor levels do to that.
The final piece is to change the meter level. You really have to drive this thing hard to make it deflect, and I don’t want that. Calculations made during a forthcoming video suggested something around 3.1kΩ would make the meter happy. I accomplished this by paralleling a resistor with the 10kΩ input, and that resistor turned out to be around 4.7kΩ. It was stuck into the holes in the terminal strip so a future owner can easily remove if needed.
With that, this project is finished. I’ll probably start a new one later to swap out those old carbon resistors - but for now, that’s all and the device is working well. There’s one more post for the wrapup, and please check out the YouTube playlist for this device.
References
Youtube playlist: https://www.youtube. … yAcib71v-995pS_-4jDr
Manual: https://wereboar.com … 0and%20Parts.pdf.zip
Fixing the speaker: https://wereboar.com … -and-final-thoughts/
Next part of this series: https://wereboar.com … -and-final-thoughts/
Previous part of this series: https://wereboar.com … ah-that-doesnt-work/
Wrapup and final thoughts: https://wereboar.com … -and-final-thoughts/