Cyrus 2 Repair Advice Needed - diyAudio
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Old 25th August 2010, 08:37 PM   #1
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Default Cyrus 2 Repair Advice Needed

I've been kindly given a Cyrus Two (Issue 07) by a friend. He had a proble with it where one of the channels went down. He sent it for repair (not to Cyrus) and it came back with both channels working, but, as he described it, with reduced volume and mains hum on it.
I've only been able to test it with headphones as I don't have speaker connections to fit (I'll get some at the weekend to try it out) but I can't hear any noise and the volume seems pretty damn loud! I presume the problem is on speaker output only.
Anyway, I've had a look inside and noticed a couple of things (see photo).
One of the fuses has a small blob of solder in the centre, as if it's blown but not completely. Is this possible and could it affect the sound?
Also, R119 (I think) seems to have been replaced and resoldered - rather badly from how it looks.
Is it possible that these could be causing issues? Any ideas would be most appreciated. I'll post more info when I test it with speakers.
Click the image to open in full size.
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Old 25th August 2010, 08:54 PM   #2
Puffin is offline Puffin  United Kingdom
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The fuse is perfectly ok. Some look like that, slow blow I think (someone will confirm)

Do you have a meter to check continuity and voltages?

Last edited by Puffin; 25th August 2010 at 09:06 PM.
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Old 25th August 2010, 09:45 PM   #3
liquias is offline liquias  Israel
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Default That's a nice amp to receive. :)

I am not sure what the problem seems to be with the amp.
One of the fuses IS a slow blow (i'm not sure about the other) and by itself should not indicate any harm. I cannot see what its rating is.

Schematics states that ratings should be 2A f.b. (thats fast blow - regular) for FS1 and FS2 and 1A s.b. for FS3 if you are on 220/240VAC grid.

Strange thing is that the rating printed on the board is nothing like the schematics state it should be.

Did the lab replace the final stage transistors ?
Are the final stage transistors original ?
Are the final stage transistors the same on the left channel as the ones on the right channel ?

Let me know if i can help with anything ...
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Old 25th August 2010, 10:02 PM   #4
lohk is offline lohk  Europe
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Location: Somewhere in Austria, near the Danube
Your description is a bit vague.

Let me look at your images:
This amp is from the late 80ies. The headphone output is directly driven by the amp itself (via resistors) so if there is a good sound the amp is working well. These outputs maybe nevertheless overdrive a 32Ohms headphone quite easy.
The fuses MUST be 4.0A fast blow, the one with the "blob" maybe is a slow blow one. If the fast blow types break when you power on the amp something is wrong.
The lower one of the "burned" resistors should actually be a diode (D12), the parts in your photo are - as far as I can remember - the circuits for the LEDs in front. This can be very easy checked. Put out the parts just in case.

Please measure at least the power supply voltages (maybe at the fuses, ground at the black speaker output). They should be symmetrical. Do not forget to check the ground connection resistor (15R) which connects the two grounds (necessary also for the use with a PSX).
The schematics are here, the Cyrus 2 is very similar (more voltage, different output transistors and drivers, but the same schematic):
The Class-A Amplifier Site
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Old 26th August 2010, 07:46 AM   #5
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Thanks for the advice. I'll replace the fuses and try some speakers on it to see what happens.
Unfortunately I don't have anyway of testing voltages etc.
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Old 26th August 2010, 08:20 AM   #6
Puffin is offline Puffin  United Kingdom
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Where in the UK are you?
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Old 26th August 2010, 08:47 AM   #7
Puffin is offline Puffin  United Kingdom
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Here is a pic of my Cyrus One. It seems that some of the components in the Two, have not been used in the One. Both fuses are 4A Fast blow.

Click the image to open in full size.
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Old 26th August 2010, 05:41 PM   #8
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Well I've tried it out with a pair of crappy Sony speakers and it seems fine. No mains hum at all, and no distortion or lack of volume.
I think I need to speak to my friend who gave it me and get him to have a listen. He has also given me the psx but I haven't used this with it, so I'll try that soon.
Any recommendations for modern, budget speakers that could go with this?
Puffin - FYI I'm in Stockport.
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Old 26th August 2010, 07:59 PM   #9
Puffin is offline Puffin  United Kingdom
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roguerobot. Glad to hear it's working as I am a long long way from Stockport in Surrey.

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Old 28th August 2010, 05:10 AM   #10
Aleko is offline Aleko  Bulgaria
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Default Mission Cambridge amplifier - switch

Hi All,

I am making use of this forum.
I have the above specified amplifier.
It is so nice, I upgraded it with Cardas connections,
speaker cable, 4 Black Gate capacitors.
Sounds wonderful after heating up for 1 hour.
But as the speaker cable appeared thick for this small box
I had to dismantle it many times in order to adjust the cable position inside and by doing so damaged the input selector switch .
The switch looks exactly the same as the ones on photos here.

Appreciate if anyone tells me where to find this switch .

Best to all

Aleko Markov
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