This week on the channel +47K views this week

A mystery amplifier opens up on The Signal Path

Shahriar repairs an Agilent signal generator, then takes the faulty chip apart for a closer look.

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The Signal Path Story of October 13, 2026Trari Newsroom

Why this story? The channel's weekly summary: what went up this week, what is drawing views now, and where the channel stands among similar channels.

TSP #348 - Mystery MMIC! Agilent E8257D 20GHz PSG Signal Generator Teardown, Repair & Experiments

A failed self-test gives Shahriar a trail to follow, but fixing the instrument isn't where he stops. The Signal Path's sole new upload ends with the faulty amplifier opened up and its tiny circuitry examined under a microscope.

The patient is an Agilent E8257D signal generator. Its filter-test error points toward a module responsible for producing the lower end of its frequency range. Shahriar uses an active probe to trace the signal step by step, narrowing the fault to a custom amplifier chip. A replacement sourced from eBay clears the error; further testing checks the generator's phase-noise performance, the small fluctuations that matter when a signal needs to be precise.

That microscopic postmortem gives the comments something substantial to discuss. A viewer identifying himself as a retired Keysight engineer recognizes the part as a two-stage amplifier and offers an explanation for its level-shifting diodes. Others ask whether the microscope images can reveal why it failed. There's also a little amusement at a lab vocabulary in which a few gigahertz can count as "low frequency."

The repair has reached about 24,000 views and is the channel's most active video right now. Behind it, Shahriar's optical-power-meter conversion continues to draw viewers, along with the detailed Tektronix oscilloscope teardown. Together, they make a particularly hands-on catch-up shelf: repair, firmware investigation and a look inside sophisticated measuring equipment.

Subscribers stayed at 144,000 over the week, while today's viewing is below the channel's usual daily level. Its weekly view gain was close to fellow electronics channel w2aew's, though both had quieter totals than Made Vision and WeatherWatchTV. For The Signal Path, the week's new contribution is one complete investigation, from an error message to the circuitry inside the failed part.

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What viewers say

Don here -- retired Keysight engineer. I recognize the mystery part, as you deduced it is a 2 stage amplifier. It's a 0.5 um GaAs MesFET process. The string of parts that you mentioned are diodes used for level shifting. This was needed since the part is DC coupled, which creates some challenges in biasing.
@djcok5315See it on YouTube
had a few of these in my grad school lab, great to see the inside!
@outside5sigmaSee it on YouTube
Is it possible to use the microscope image of the defective ampflifier to find out why it is broken?
@lbgstzockt8493See it on YouTube

6 more comments

34:17 "And I believe this is upside down." Astute listeners will notice that there is no disclaimer about the electrons falling out. Presumably that is only a problem in the southern hemisphere - from which we can deduce that electrons _fall upwards_ under normal circumstances. The more you know.
@PasilBestoSee it on YouTube
Great video as always! Another old Agilent repair reminds me that there's a 13.5GHz PSG sitting in the lab with a dead SLODA that I need to work on...
@MPAtk03See it on YouTube
I love supporting this channel, these videos are so fascinating and you can't find this type of content anywhere else! I particularly love the fault finding repair types like this, always interesting reasoning through the problem with you guiding it. Amazing die shots. Could the flux and residue on the IC from the previous solder job been the issue since the die looks pretty good?
@JFirn86QSee it on YouTube
Great presentation, thanks for all you do. And your videos are never too long!
@5530fscSee it on YouTube
this is a must watch for ee students
@quantumality0084See it on YouTube
Beautiful work and presentation as always, thanks.
@BaconbuttywithCheeseSee it on YouTube