# 005 - Circuits That Go Nowhere

- Show: [Unnamed Reverse Engineering Podcast](https://hardwarepodcasts.com/podcast/unnamed-reverse-engineering-podcast)
- Published: 2017-11-06
- Length: 57m
- Page: https://hardwarepodcasts.com/podcast/unnamed-reverse-engineering-podcast/2017-11-06-005-circuits-that-go-nowhere
- Listen: https://unnamedre.com/episode/5

## Summary

Ken Shirriff, a reverse engineer and blogger, details his process for reverse engineering vintage integrated circuits, from decapping chips using safe acids to analyzing die photos with metallurgical microscopes. He discusses the restoration of the Xerox Alto computer, explaining how he and collaborators resolved hardware mismatches and reverse-engineered its complex microcode using logic analyzers. The conversation covers specific historical chips like the 8008 and Z80, highlighting design quirks such as 4-bit ALUs in 8-bit processors and the use of current mirrors in analog circuits.

## Chapters

- [0:15](https://hardwarepodcasts.com/podcast/unnamed-reverse-engineering-podcast/2017-11-06-005-circuits-that-go-nowhere#t=15) Introduction: Ken Shirriff and his blog righto.com
- [3:26](https://hardwarepodcasts.com/podcast/unnamed-reverse-engineering-podcast/2017-11-06-005-circuits-that-go-nowhere#t=206) Decapping chips and safe acid techniques for hobbyists
- [8:42](https://hardwarepodcasts.com/podcast/unnamed-reverse-engineering-podcast/2017-11-06-005-circuits-that-go-nowhere#t=522) Using metallurgical microscopes and XY stages for die photos
- [12:31](https://hardwarepodcasts.com/podcast/unnamed-reverse-engineering-podcast/2017-11-06-005-circuits-that-go-nowhere#t=751) Reverse engineering the 8008 and Z80 microprocessors
- [17:38](https://hardwarepodcasts.com/podcast/unnamed-reverse-engineering-podcast/2017-11-06-005-circuits-that-go-nowhere#t=1058) Analog circuit tricks: current mirrors and strange transistors
- [27:12](https://hardwarepodcasts.com/podcast/unnamed-reverse-engineering-podcast/2017-11-06-005-circuits-that-go-nowhere#t=1632) Identifying counterfeit chips and repackaged DTMF encoders
- [37:34](https://hardwarepodcasts.com/podcast/unnamed-reverse-engineering-podcast/2017-11-06-005-circuits-that-go-nowhere#t=2254) Restoring the Xerox Alto and fixing hardware mismatches
- [44:18](https://hardwarepodcasts.com/podcast/unnamed-reverse-engineering-podcast/2017-11-06-005-circuits-that-go-nowhere#t=2658) Reverse engineering Alto microcode with logic analyzers
- [51:37](https://hardwarepodcasts.com/podcast/unnamed-reverse-engineering-podcast/2017-11-06-005-circuits-that-go-nowhere#t=3097) Advice for starting in IC reverse engineering

## Topics

- [Chips, FPGAs & semiconductors](https://hardwarepodcasts.com/topic/chips-and-fpgas)
- [Debugging & failure analysis](https://hardwarepodcasts.com/topic/debugging-and-failure-analysis)
- [Analog & power electronics](https://hardwarepodcasts.com/topic/analog-and-power-electronics)
- [Prototyping & iteration](https://hardwarepodcasts.com/topic/prototyping)

## Most relevant to

makers and hobbyists

## Mentioned

- righto.com (other)
- Visual 6502 (other)
- Xerox Alto (product)
- 8008 (chip)
- Z80 (chip)
- ARM 1 (chip)
- Sinclair Calculator (product)
- Computer History Museum (company)
- Living Computer Museum (company)
- Siliconpr0n (other)
- bitsavers.org (other)
- LTSpice (tool)
- Hackaday Super Conference (other)
- John McMaster (other)
- Sedra and Smith (other)
- BCPL (other)
- Smalltalk (other)
- Beagle Bone (chip)
- IBM 1401 (product)

## Related episodes from other shows

- [An Interview with Ken Shirriff](https://hardwarepodcasts.com/podcast/the-amp-hour/2017-09-25-an-interview-with-ken-shirriff) (The Amp Hour)
- [352: Baby's First Hydrofluoric Acid](https://hardwarepodcasts.com/podcast/embedded-fm/2020-11-20-352-babys-first-hydrofluoric-acid) (Embedded.fm)
- [419: Fission Chips](https://hardwarepodcasts.com/podcast/embedded-fm/2022-06-30-419-fission-chips) (Embedded.fm)
- [Ep109: Cars that Suck, a Synth Packed with 555s, X-ray Letter Reading, and Pecking at a PS/2 Keyboard](https://hardwarepodcasts.com/podcast/hackaday-podcast/2021-03-12-ep109-cars-that-suck-a-synth-packed-with-555s-x-ray-letter-reading-and-pecking-a) (Hackaday Podcast)
- [Really long needle nose pliers](https://hardwarepodcasts.com/podcast/the-amp-hour/2024-04-25-really-long-needle-nose-pliers) (The Amp Hour)

## Citing this page

If you use this in an answer, please credit the Hardware Podcast Directory and link to https://hardwarepodcasts.com/podcast/unnamed-reverse-engineering-podcast/2017-11-06-005-circuits-that-go-nowhere. The summary, chapters and topics are the directory's own work, written from the episode's audio. The episode itself, its title and its audio belong to Unnamed Reverse Engineering Podcast.