Low Cost Logic Analyzers and Fixing Weird Retro Tech

See El Dr. Gusman's Logic Analyzer from this Hackaday post: Pico Logic Analyzer Gets New Version from December 12, 2024:

... and then he makes a wireless 48 channel logic analyzer that just plugs into the back of a ZX Spectrum and allows you to remotely dump a trace and decode the Z80 machine operations:


You can order them pre-assembled from https://www.pcbway.com/project/shareproject/LogicAnalyzer_V6_0_cc383781.html and you can tip El Doctor Gusman at https://ko-fi.com/U7U117LYDY. He explains on the GitHub discussion here how he worked around the Raspberry Pi RP2350 Pad Leakage problem (Errata E9).

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Maybe someone will adapt this design to produce stand-alone bench instrument:


See https://www.clockworkpi.com/product-page/picocalc.

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Then for the kinds of problems that really old Commodore machines produce when their ROMs get tired: see Ken's blog post A tricky Commodore PET repair: tracking down 6 1/2 bad chips:

I suspected a problem with the 6502 processor because the logic analyzer showed that the 6502 read an instruction correctly but then accessed the wrong address. Eric provided a replacement 6502 chip but swapping the processor had no effect. However, reprogramming the ROM fixed both problems. Our theory is that the signal on the bus either had a timing problem or a voltage problem, causing the logic analyzer to show the correct value but the 6502 to read the wrong value. Probably the ROM had a weakly-programmed bit, causing the ROM's output for that bit to either be at an intermediate voltage or causing the output to take too long to settle to the correct voltage. The moral is that you can't always trust the logic analyzer if there are analog faults. 

Very early on in the process it was noted that the EPROM programmer was not using a high enough programming voltage and the first pass failed, but a second pass was verified OK by the EPROM programmer, ...


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