UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Cyrus III amplifier

samjmann · 3rd Jul 2021, 8:28 pm

Thank you for all the replies, I've followed Refugee's sage advice.

The the main amp board is now back in the chassis, which is the the top cover and heatsink. Quite a fiddly job getting the output transistors and isolating washers all aligned.

I mentioned on my last post about a channel imbalance on certain inputs - this is still present. On the the tuner and Au inputs both outputs are identical. But on CD and VI the signal is much greater on the left than before. To make things clear, the Rh isn't low, it's the left that actually increases in level.

If you look at the circuit snipits on IC107A pin 1 from my test disc the level rose from 1v P.P to 3vP.P when I swopped from tuner to CD.

I cannot monitor the input signal to IC107-A as its so small. All I can think is that there is a problem with IC101/103. Both of these are surface mount DIL 16pin, I want to be as sure as I can before removal

Any thoughts about this?

At first I thought the RH was low, its actually that the LH is HIGH only on certain inputs.

Regards SJM.

3rd Jul 2021, 8:28 pm	#11
samjmann Heptode Join Date: Feb 2014 Location: Nottingham, UK. Posts: 648	Re: Cyrus III amplifier - output stage failure. Thank you for all the replies, I've followed Refugee's sage advice. The the main amp board is now back in the chassis, which is the the top cover and heatsink. Quite a fiddly job getting the output transistors and isolating washers all aligned. I mentioned on my last post about a channel imbalance on certain inputs - this is still present. On the the tuner and Au inputs both outputs are identical. But on CD and VI the signal is much greater on the left than before. To make things clear, the Rh isn't low, it's the left that actually increases in level. If you look at the circuit snipits on IC107A pin 1 from my test disc the level rose from 1v P.P to 3vP.P when I swopped from tuner to CD. I cannot monitor the input signal to IC107-A as its so small. All I can think is that there is a problem with IC101/103. Both of these are surface mount DIL 16pin, I want to be as sure as I can before removal Any thoughts about this? At first I thought the RH was low, its actually that the LH is HIGH only on certain inputs. Regards SJM. Attached Thumbnails __________________ It's never been right since we've had it...