EEVblog 1771 – A Tricky OpAmp Exam Question

Part 2 of the PayPal Here teardown, because everyone wanted to know what was under the anti-tamper security mesh, so lets take a look. Datasheet: https://www.nxp.com/docs/en/data-sheet/IMX25CEC.pdf 00:00 – We return to the PayPal Here POS terminal teardown 04:11 – They want to stop Skimming hacks, it’s not just the keys 07:39 – Removing the keypad security mesh + a SURPRISE! 11:31 – On-die physical security 12:09 – Removing the card reader security anti-tamper mesh 13:36 – Speculating on hacking this POS terminal Forum: https://www.eevblog.com/forum/blog/eevblog-1773-paypal-here-pos-terminal-teardown/

Teardown of the now obsoleted PayPal Here POS Payment terminal. 00:00 – PayPal Here POS payment terminal 03:56 – Teardown 05:10 – Case security clips 06:31 – Battery 08:02 – Security tamper mesh 10:43 – POS Terminal companies and my job at KeyCorp 12:14 – Bye Bye secure keys 14:24 – Battery removal 16:29 – i.MX258 Secure ARM processor Links: https://www.nxp.com/docs/en/data-sheet/IMX25CEC.pdf https://listings.pcisecuritystandards.org/documents/pci_pts_poi_sr.pdf Forum: https://www.eevblog.com/forum/blog/eevblog-1773-paypal-here-pos-terminal-teardown/

A follow-up to the previous video showing the complex AC impedance answer to the OpAmp exam question. Part 1: https://www.youtube.com/watch?v=nDEGqme5Z4g https://www.eevblog.com/forum/beginners/how-to-analyze-the-opamp-circuit/ OpAmp playlist: https://www.youtube.com/playlist?list=PLvOlSehNtuHu2FviAaZaiyXwN41G4b1Lf

Dave answers an exam question on OpAmps that’s interestingly tricky. Bonus opamp tutorial on biasing. Part 2: https://www.youtube.com/watch?v=33rS0oLULqw https://www.eevblog.com/forum/beginners/how-to-analyze-the-opamp-circuit/ OpAmp playlist: https://www.youtube.com/playlist?list=PLvOlSehNtuHu2FviAaZaiyXwN41G4b1Lf 00:00 – A tricky exam question 01:45 – What’s missing? 03:11 – The two most important Opamp rules 04:44 – THINK about what sort of exam you are in BEFORE answering the question 07:04 – Capacitive reactance “AC resistance” 08:53 – They want you to use frequency, but also IGNORE it? How does that work? 10:21 – When it doubt, assume a short circuit 10:59 – Solving the first part of the question 12:20 – The 2nd rule of AC circuit analysis 13:33 – Solving the second part of the question, what is the AC gain? 15:29 – There is no need to muck around, move on to the next question 15:58 – Let’s talk about Opamp Biasing 22:59 – Single pole high pass filter 23:31 – Ripple removal filter 26:24 – Conclusion, why is this question is clever?

Teardown and reverse engineering of the new Rigol RSA800 series Real Time Spectrum Analyser, from 4.5GHz to 13GHz. 4.5GHz RSA804 8.5GHz RSA808 14GHz RSA814 https://www.rigolna.com/products/spectrum-analyzers/rsa800/ 00:00 – Rigol’s new RSA800 Real Time Spectrum Analyser 06:48 – Teardown 11:42 – RF front end box teardown. Mad Man Muntz 14:55 – Back side of the RF block 16:50 – Reverse Engineering with DaveCAD 22:05 – Attenuator & Preamplifier 23:41 – Interesting split into separate HF and LF mixers 25:47 – Preselect filters 27:33 – Flux residue! 28:23 – HF and LF Mixers and 1st stage PLL 30:58 – Downconversion mixing explained 32:48 – 2nd Stage Active IF Mixer, now we are getting serious 36:01 – Final 3rd stage active mixer 36:57 – Dave is WRONG, but why you might want two ADC’s vs one 39:20 – No Dave, it’s a DAC 40:25 – Speculating on the custom ADC used, and digital quadrature sampling 41:49 – Mystery LTC part, and what on earth is going on here with these PCB couplers? 44:32 – Teardown Conclusion 45:51 – Demo comparison of a DSA815 and RSA808, Real Time vs Swept Analysis Forum: https://www.eevblog.com/forum/testgear/new-rigol-rsa800-spectrum-analyser/ Hi-Res Photos: Datasheets: SIS378 Switch: https://www.sicoresemi.com/ueditor/php/upload/file/20250818/1755497980219246.pdf SIAT116 Attenuator: https://www.sicoresemi.com/ueditor/php/upload/file/20260427/1777277733715489.pdf LF Mixer : https://www.sicoresemi.com/ueditor/php/upload/file/20250923/1758612877124723.pdf SIM445 HF Mixer: https://www.sicoresemi.com/ueditor/php/upload/file/20260709/1783577453983448.pdf SIA070 Amplifier: https://www.sicoresemi.com/ueditor/php/upload/file/20260509/1778310579506957.pdf SIS119 Absorptive Switch: https://www.sicoresemi.com/ueditor/php/upload/file/20250324/1742806808125089.pdf SIP052 Phase Converter: https://www.sicoresemi.com/ueditor/php/upload/file/20240627/1719477861130248.pdf SIA332 Amplifier: https://www.sicoresemi.com/ueditor/php/upload/file/20240924/1727159790115927.pdf LMX2820 PLL: https://www.ti.com/lit/ds/symlink/lmx2820.pdf LTC5577 Active Mixer: https://www.analog.com/media/en/technical-documentation/data-sheets/5577f.pdf

Can you repair a PSU by REMOVING a component? Well, in this case, yeah, kinda. Not recommended for new designs, but it works (for now) because the design margins allowed it. 00:00 – My NerdQaxe++ Bitcoin miner has failed. Guru Meditation! 02:13 – Bitmain 1370 chipset thermal paste 03:54 – The flipchip die under the microscope 04:48 – Thermal paste application triggering 06:55 – Time for a new strategy R2. The Vreg temp sensor is now the suspect 07:53 – A look at the open source hardware schematic in KiCAD https://github.com/shufps/qaxe 09:42 – The TPS53647 4 Phase ASIC Buck PSU controller https://www.ti.com/lit/ds/symlink/tps53647.pdf 10:23 – The CSD95472Q5MC Synchronous Buck NexFET Smart Power Stage https://www.ti.com/lit/ds/symlink/csd95472q5mc.pdf 11:50 – We can try wacking a heatsink on + Jaycar field trip 12:41 – Did that fix it? 14:10 – It’s becoming obvious what the fault is now 16:24 – Thermal camera testing 16:56 – Oscilloscope time on the 3 phase PSU 18:21 – Desoldering time, maybe 19:42 – Will removing this component work? 23:52 – AutoBalance multi-phase buck conversion for the win Forum: https://www.eevblog.com/forum/blog/eevblog-1769-repair-by-removing-a-component/

More Mailbag! 00:00 – Dave & Dylan open random Mailbag 03:49 – DIY bodged laser engraver 04:14 – MPPT Solar charge controller 04:56 – Mixed bags 06:01 – DLP Projector Mirror Arrays 08:05 – TDA2030A Power Amp 08:39 – Analog/Digital combo watch 12:23 – Solar Panels 13:52 – Engineering Spelling + 34401A VFD Replacement https://hubequip.net/products/hp-agilent-34401a-vfd-to-led-display-replacement-led-conversion 17:58 – Treedix USB Cable Tester https://treedix.com/ 24:33 – Zoyi ZT-XC1 Combo LCR & Multimeter https://s.click.aliexpress.com/e/_c4kzCJV5 Forum: https://www.eevblog.com/forum/blog/eevblog-1768-mailbag/

Teardown and detailed analysis of the Harogic PXN-90 9GHz Spectrum Analyser. https://www.harogic.com/product/harogic-px-series-standard-spectrum-analyzer-receiver/ Forum: https://www.eevblog.com/forum/blog/eevblog-1767-harogic-pxn-90-9ghz-spectrum-analyser-teardown/

Dave’s Rode PodMic USB failed, so might as well do a quick teardown before returning it under warranty. Forum: https://www.eevblog.com/forum/blog/rode-podmic-usbs-are-failing!/

Using an Waveshare ESP32 RS485 module on the Brink Flair 400 home air ventilation system to email alert if the inlet pressure goes about 400 pascals. And using Claude AI to generate the Arduino code required. 00:00 – Brink Flair 400 ventilation system 02:04 – Waveshare ESP32-S3-RS485-CAN module 06:32 – Using Claude to generate Arduino code 17:04 – Pirate Mode Activated 24:21 – Installation and testing