Hi All I'm troubleshooting a Sharp CD-370E cd/tuner/tape-deck combo. It's probably about 15+ years old - probably beyond economic repair, but it's a 'sentimental value' job as it belonged to my late Dad.
Unit worked fine when put into storage a couple of years ago - but doesn't work now.....
Symptoms - no fluorescent display, but CD system does seek when a CD is inserted.
Have checked the PSU - all voltages present & correct. The Sharp service manual suggests a sequence of troubleshooting as follows
- Check Power voltages - OK
- Check Oscillator Circuit on control micro - OK, seen via 'scope
- Check to see that the reset circuitry of the control micro is operating normally -
here's where I need guidance - as to 'what' constitues 'normally'.
The unit has internal reset circuitry on the main control board - using a PST600D IC. This device connects to the control micro's RESET pin. I'm guessing that I should see a low level on this pin when power is first applied, followed by 5V after a suitable delay - sound right??
There's also a 'hard reset' via a switch on the back panel - which not only pulls on the RESET line but also seems to pull down the micro's
5V line. Oddly, pressing this button doesn't cause either of these pins to drop significantly - although, viewed at the reset button, the 'hot' end of the reset button does get pulled to 0V.Sorry if this is all very basic stuff - but my audio experience is very much in the era of 'audio gear that didn't have micros in it' - where much trouble-shooting could be done with the application of a wet finger at various points in the signal path......
At the moment I'm working on the basis that the micro's not getting a 'proper' reset, and so it's not running correctly. As the micro enables various power supplies, I'm thinking that this could account for the lack of activity around the unit.....
Any suggestions / pointers welcomed Thanks in advance Adrian - Suffolk UK ======return email munged================= take out the papers and the trash to reply