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8-bit acorn hardware • Re: Fault finding index

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BBC Micro Model B tape only. Doesn't boot, continuous tone, black screen.

Put in Tricky's Test ROM and still nothing.

As it has a tone, it isn't the main clock failure, so I checked the 1,2,4,8 MHz clocks and they were all present. Checking the address bus lines and they were looking relatively normal in shape, checked the data bus lines and noticed bit 0 and bit 1 were mangled.

I removed the 6502 and using a multimeter noticed a 4R reading between D0 and D1. Flipping the board over I noticed someone had done some rework, I waved the ToneOhm over the board it was screaming when I got to the vicinity of the rework around a pair of recently fitted sockets for IC71 and IC72.

Careful examination of the board revealed some poor quality rework had managed to bridge a track from pin #18 on IC72 (D0) with a track from pin #15 on IC72 (D1) removal of this solder blob and the Beeb started up and went through the diagnostics perfectly and then after an OS ROM swap, booted up into BASIC with no problems. I repaired the lacquer and re-soldered all the pins (the soldering was quite grotty) I then installed Econet and all is good.

Statistics: Posted by maniacminer — Sat Jan 11, 2025 8:35 pm



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