Hello!
I recently acquired a Cyrus iii amplifier for cheap and was wondering if it's worth more than parts. I would really like to fix it but I'm not quite sure where's the problem. When I turn it on with the power switch in the back, amplifier displays different combination of leds (see attached pictures) almost every time and the front panel buttons or volume control aren't responsive. Power indicator shows green or both green and red at the same time. I guess that there is a communication problem between the chips in the front board (the one with the buttons). Can anyone confirm my suspicion? I've soldered and desoldered surface mount components before (no destroyed pcbs so far), so I'm willing to give it a try to repair the board.
I recently acquired a Cyrus iii amplifier for cheap and was wondering if it's worth more than parts. I would really like to fix it but I'm not quite sure where's the problem. When I turn it on with the power switch in the back, amplifier displays different combination of leds (see attached pictures) almost every time and the front panel buttons or volume control aren't responsive. Power indicator shows green or both green and red at the same time. I guess that there is a communication problem between the chips in the front board (the one with the buttons). Can anyone confirm my suspicion? I've soldered and desoldered surface mount components before (no destroyed pcbs so far), so I'm willing to give it a try to repair the board.
Attachments
In the first instance you would need to check all the supply voltages are correct (first rule of fault finding). Beyond that the problem could be 'anything' but I would begin by looking for things such as the possibility of some of the actual switches being stuck on and giving a non valid input to the system control.
Also look and see if there is any form of backup supply (battery or 'Supercap') and if so consider removing that to reset the logic and see what happens.
But... it could be anything 🙂 You have to go in and look and measure and ideally have a full and correct diagram in front of you.
Also look and see if there is any form of backup supply (battery or 'Supercap') and if so consider removing that to reset the logic and see what happens.
But... it could be anything 🙂 You have to go in and look and measure and ideally have a full and correct diagram in front of you.
Just as Mooly suggests, I would firstly check the power suplies especially around the microprocessor.
Check VR501. It is a 7805 and can be prone to dry joints.
Carefully check the oscillator pins 7 & 8 of IC501for oscillation and ensure pin17 has a good reset pulse and pin 15 of the 4094 chips. No/poor reset pulse and random things will happen.
Check VR501. It is a 7805 and can be prone to dry joints.
Carefully check the oscillator pins 7 & 8 of IC501for oscillation and ensure pin17 has a good reset pulse and pin 15 of the 4094 chips. No/poor reset pulse and random things will happen.
I did repair one of these a long time ago. Check for DC offset at the power transistors. These would blow also taking out the driver transistors. It was a fairly easy to replace the parts and get it working. The compact design is not for situations requiring continuous high power use. After repair it blew again because it was being asked to drive a big inefficient speakers in a large space.