06-03-2012, 07:46 PM
(06-03-2012, 05:50 PM)ed731pdh Wrote: Managed to obtain a diag for the computer, what a mess.
No it's not
Quote:Each sound channel is fed to the final amp stage via a seperate op amp. There are four op amps in the same package so it is concievable that one of the amps could go down and remove that particular channel feed.
No, that's not how it works. The sound chip (IC18) contains 3 tone generators and 1 noise channel. The combination of all of these emerges on pin 7. This travels through R5 into the summing amplifier IC17d. This sums other signals, such as the rarely-fitted speech synthesis chip (IC99), and an input from the 1MHz bus. Following on from the summing amplifier, IC17c is a low pass filter, ahead of the output amplifier.
Quote:The burrr part of the beep is apparently caused by stray signals on the data line that float around until the 555 timer initiates the data bus.
Yes, that's always been my assumption too.
However, you didn't answer the key point I raised: after the "burr", do you definitely get the "beeb"?
Mark
