The EICO 150 Solid State Signal Tracer Part 2: Capacitors…capacitors everywhere!
Tuesday, April 28, 2026 at 06:01:26
This device has a lot of little capacitors all over the place. Interstage, coupling, bypass, etc. There’s even a multi-section filter array underneath. Most of the small ones were bad, as in >90Ω ESR bad.
Replacing the capacitors in the EICO 150
Here’s what we’re working with. This is a “Type 1” assembly, and has a mix of topside and bottom chassis parts:
I decided to go with all good stuff here. Small capacitors are Wurth, larger ones are Vishay or IC. As this is a single sided board, it was easy enough to heat the joint, pull the part, and then clean up the pad with some wick. New capacitors were bent as to provide leads to each pad, or folded over as needed. Parts on the bottom were simply patched in place of the previous part.
The ones that were really bad were all of the little 1μF 15V parts. Every one of these was well past useful with ESR measurement. Some of the larger ones were tired, but ok, with the filters being acceptable - although appearing to have been replaced at some point in their life already.
Every capacitor in here that’s an electrolytic has been replaced. I did a quick check on those teal blue ones, as I’ve found those to be shorted in other EICO devices. These seemed to be ok, but it would be best that those get replaced as well.
Testing the repair
The gain is certainly much higher now - 1KHz test tones are loud enough to damage your hearing. I tried a radio source, it doesn’t seem to have enough gain here - but that could be impedance matching isn’t very good, as the radio’s drive is nothing more than the low-level output of the demodulator IC itself. I need to look into this a bit more. There’s also some wiring I want to clean up in this unit, just because it’s not tacked together well. That will come with the other capacitor replacements.
It works, and is probably good enough at the moment. We’ll get come back to this one soon enough.
It’s not good enough and has some transistor biasing issues, as well as some WTF from the previous owner.
Notes
The transistors this thing uses, or can use:
2x 2N3391A. - These are generally obsolete, but can still be found easily enough.
1x 2N3906 - These are common as dirt.
1x NTE152 - This is the final output and is becoming scarce, although is still available.
If you have one of these devices, it may be wise to stock a few of the obsolete parts.
Next part of this series: https://wereboar.com … t-3-its-wired-wrong/
Previous part of this series: https://wereboar.com … part-1-observations/
Wrapup and final thoughts: Coming soon.