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SiriusHardware · 2nd Jan 2018, 1:27 am

It's a shame I didn't know you were going to pose this question as I recently intercepted three or four new-old-stock 8085A CPU ICs on the way to the WEEE waste. One is an original Intel part, the others are other-manufacturer clones (Toshiba, NEC).

Warm running does not necessarily indicate a fault in CPUs of this era, although excessive heat does. By excessive, I mean, you can't even keep your finger on it after a minute or so. Anything less warm than that could be quite normal.

The weird crystal frequency will (like nearly all weird CPU crystal frequencies) be something to do with either tone frequency generation/detection or baud rate generation - in this case most likely the latter.

The trick of using a receiver to 'sniff' an oscillator which might stop dead if you connect a scope directly to it is an old favourite of mine as well, but it's also worth switching your scope probe to X10 and increasing the sensitivity of the scope channel by ten and trying again.

That EPROM with the unprotected window is making me quite nervous, if it has always been like that then you could be suffering from data fade in the EPROM, assuming that's where the firmware is.

2nd Jan 2018, 1:27 am	#16
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,556	Re: 8085 processor questions It's a shame I didn't know you were going to pose this question as I recently intercepted three or four new-old-stock 8085A CPU ICs on the way to the WEEE waste. One is an original Intel part, the others are other-manufacturer clones (Toshiba, NEC). Warm running does not necessarily indicate a fault in CPUs of this era, although excessive heat does. By excessive, I mean, you can't even keep your finger on it after a minute or so. Anything less warm than that could be quite normal. The weird crystal frequency will (like nearly all weird CPU crystal frequencies) be something to do with either tone frequency generation/detection or baud rate generation - in this case most likely the latter. The trick of using a receiver to 'sniff' an oscillator which might stop dead if you connect a scope directly to it is an old favourite of mine as well, but it's also worth switching your scope probe to X10 and increasing the sensitivity of the scope channel by ten and trying again. That EPROM with the unprotected window is making me quite nervous, if it has always been like that then you could be suffering from data fade in the EPROM, assuming that's where the firmware is.