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Old 26th December 2011, 09:05 PM   #1
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Default Cyrus 3 help needed

Hi There
Can anyone help? I've purchased a faulty Cyrus 3 on Ebay. The original fault was lights fleashing and blinking, nothing works. I've worked out that the voltages to the microprocessor board are wrong. +5.5V in and +3.6v out. I'm expecting 5v out so the input I reckon should be 8 to 10v (Im talking about the 7805 voltage regulator on the contoller board)
Anyway, I'm not going to attempt a repair as I think the fault is somewhere on the power amp board and there are smts everywhere. But all the voltages to the power amp stages look ok so I'm thinking of bypassing the input and volume circuits altogther. Does anyone know where to connect an input directly into the power amplifier stage?

I'm willing to cut pcb tracks and hard wire in one of the phono input pairs. I know that there is got to be a capacitor as the input but which one?? Also, can someone send a photo of the controller board as removed the 7805 voltage reg and the microprocessor but don't know which way around they go back and it's not marked on the board.
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Old 27th December 2011, 04:19 AM   #2
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Hi
There are schematics here, Cyrus III power amp schematic here, but schematics of the later models wanted

Always a good start to any repair or fault find.

Cheers / Chris
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Old 27th December 2011, 06:16 AM   #3
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The links don't work for me
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Old 27th December 2011, 06:43 AM   #4
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Cyrus 3 Power amp schematic

Cheers / Chris
Attached Files
File Type: pdf Cyrus III.ckt.pdf (23.7 KB, 53 views)
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Old 27th December 2011, 09:07 AM   #5
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Thank you for that. I should be able to work things out with those schematics. I've put the 7805 and microprocessor back properly as there are marks on the board....just didn't see them.

This project has started as a bit of fun over Christmas but I'm not gonna get drawn into it too much. I'll use it as a power amp by getting rid of all the switching and volume circuits. I'll measure the gain of the power stage and add in my own input circuit if I need to.
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Old 28th December 2011, 10:46 AM   #6
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I've noticed the schematics you've given don't bear much resemblance to what I see on the circuit board. My amp is a Cyrus 3 but the schematics say Cyrus 3i. Is there much difference or is one a variation of the other? Does anyone know from where the power to the microprocessor board comes from?
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Old 28th December 2011, 11:04 AM   #7
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Quote:
Originally Posted by andy_kaye View Post
I've noticed the schematics you've given don't bear much resemblance to what I see on the circuit board. My amp is a Cyrus 3 but the schematics say Cyrus 3i. Is there much difference or is one a variation of the other? Does anyone know from where the power to the microprocessor board comes from?
Hi Andy
I would look up Cyrus's site, most of this equipment came from Cambridge England.
Mission audio Contact

back to your first question on this post, errors with Voltage regulators like you describe often arise from reversal of Gnd for Vin, Possibly from having a Regulator around the wrong way a 7815 or 7805 is from the front Vin Gnd Vout, .... and 7915 or 7905 Gnd Vin Vout.

The second part of your question power for the microprocessor is most likely to be from a 7805. I would carefully check the PSU for such errors.

Cheers / Chris
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Old 28th December 2011, 11:29 AM   #8
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Hi Chris

Thank you for that advice. I will check carefully if the regulators are seated the right way. Thinking about it I can't assume that they are because I don't know the history of the amplifier. I'm focusing in on the power regulators as circuit board show signs of overheating around them. Now I'm starting to wonder if I should take what I see at face value. There are 2 7915s and 2 7815s on the circuit board which I find a bit odd, the shematics are quite different. The only trouble is that the schematics have numbers on them that don't correspond with numbers on the circuit board. So far, I've only been working on it casually but I might put a bit of determination in today.
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Old 28th December 2011, 11:41 PM   #9
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The Cyrus 3 has 3 variants apart from your later 3i version which obviously added the micro controller. However, all the SMD Cyrus 3 amplifier schematics are similar. Obviously the controller. PSX and PCB designs are not. Damage could have occurred simply by connecting the wrong PSX type , bad connections or simple component failures.

3-terminal regulators dissipate heat because they are designed to do so in order to regulate, so you can expect the PCB to discolour when they are in close proximity, particularly in circuits that remain on when the amplifier is not.

Other forums like hfd have discussed recommended sources of info on the 3 but many links are now broken. Search your Cyrus 3i as posts on this forum and go through the threads and links as best you can but unless you locate the exact 3i schematics. you won't find correlations of part numbers and values and connecting leads that you may hope for.

If he is able to respond, Moderator Anatech is a service agent for Cyrus and whilst due to Cyrus policy, he can't offer you schematics, he may know of the likely problems to assist in getting help elsewhere.

Edit: Of course one point of a controller board is often to shut the amp doiwn and indicate a faults condition, as you appear to have. I would look at the output stage for obvious toasted parts there in the first instance.
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Last edited by Ian Finch; 29th December 2011 at 12:09 AM.
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Old 30th December 2011, 06:27 AM   #10
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Interesting schematic. The short protection in the schematic posted by Chris is only reducing the drop of the Vbe multiplier, so not a true protection. I don't like opto isolators to carry high levels of high frequency common mode, most of them are only really for blocking mains frequency and dc.

I would remove the suspect 7805 and power the amplifier with a series 100W light bulb and see what the input voltage is under no load. 3V6 is about what you would expect from a 7805 with 5V5 in and moderate load.
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