Keeping my Cyrus Two alive...

[captainsemtex]

I have a Mission Cyrus Two amplifier which I purchased in 1985 along with the PSX power supply. The Cyrus Two PCB is issue 4.

It's working very well for a 35 year old amplifier. I usually subscribe to the "if it 'aint broke don't fix it" mentally, but in this case I want to be more proactive.

(As I write this I am listening to Thelma Houston/Sheffield Labs via the Cyrus Two/PSX and my similar era Oracle Alexandria turntable and it sounds excellent. I want to keep it that way!)

Remembering that I have an Issue 4 PCB and use the PSX supply, what components should I be looking to replace on the Cyrus Two PCB? In other words, what are common failure points?

The only problem I have had in recent times is an intermittent right channel on both the MM and MC phono inputs (the CD, Tuner and Tape inputs are all good). I've tried the usual cleaning methods and currently the MC input is working reliably though MM is still intermittent. So replacing the PCB mounted phono sockets for the MM and MC inputs is one thought... but I cannot find a source for those components.

Additionally VR1 and VR2 voltage rectifiers seem to be running hotter than I remember, but that could be a red herring.

Any advice is appreciated... as are any pointers to the Cyrus Two service manual (I found the issue 6/7 manual but nothing for Issue 4).

Thanks in advance.

[ajgriff]

Hello and welcome. Interesting point about the manual. At the beginning of the issue 6/7 manual it states that issue 6 was the first version of the Cyrus 2 which conflicts with my recollection and the existence of your issue 4 amplifier. However, I've never been able to find a manual for an earlier version either.

If the amplifier is performing well and there are no signs of component deterioration (electrolytic capacitors in particular) I'd be inclined to leave well alone. The MM intermittency probably just comes down to the need for a little switch cleaner. It might also be worth checking the DC offset and quiescent current conditions as described in the manual.

Alan

[captainsemtex]

Thanks for the reply Alan and sorry I did not see this earlier. For some reason I did not spot the notification of a reply.

You are right that the service manual does indeed say that Issue 6 is the first version and my serial number 201725 falls inside the issue 6 range. I should have taken a photo while the top was off!

LOL, I never thought the problem could be the switch... and that would be an easy fix. That's my job for the weekend.

Thank you.

[Beobloke]

The upward facing phono sockets are an issue on these but there should be no need to replace them if they aren't causing too many problems - just take the board out and re-solder them all.

[Radio Wrangler]

Depending how firms do revision control, you can get some rather confusing markings... for example the printed circuit board design might be that of revision C but a few iterations of component value changes have happened, so the loaded PCB assembly might be revision G, but as there was no need to make changes to the board artwork, the board could still be marked C.

Confuses the hell out of the people in the field!

HP used to handle this by having the boards and assemblies using them on separate revision series, but they loaded a little etched metal label (auto-inserted and soldered) as a component stating the rev of the assembly. So if you changed a material list for a board, you switched the part number of the label to the part number of the next rev. So long as you knew of the arrangement, there was no confusion.

David

[ajgriff]

Originally Posted by Beobloke

The upward facing phono sockets are an issue on these but there should be no need to replace them if they aren't causing too many problems - just take the board out and re-solder them all.

Sound advice. Had exactly the same issue with a Yamaha amplifier recently. Re-flowing the solder joints to the phono sockets provided an instant cure.

Alan

[John Caswell]

Had several of these in for intermittent phonos, usually where they are soldered to the PCB. My solution was to wire them directly to the next PCB land, following the track routes as far as possible, with thin stranded Teflon insulated wire and a spot of hot melt glue to keep them in place.

John

[vidjoman]

Big problem is that some people use big phono plugs with cables that could tie up a ship. They are tight fitting and often break the solder joints if the socket is fitted directly to the PCB. This seems worse when the sockets are mounted flat as in the Cyrus and NAD amplifiers. Just the weight of thick cables can cause broken joints.

It is only worth fixing real faults, no hope in pre empting future ones.