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Old 28th March 2007, 10:57 AM   #1
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Question Cyrus 2 Resistors

Hi there

I'm a newbie to the forum - I've just hard shorted the right hand output of my Cyrus 2, from visual inspection it looks like several resistors have blown. I've been goggling for the resistor colour code but I cant seem to read it from these. Does anyone now what the direct replacements would be ?

I've included a photo of the damage

http://www.flickr.com/photos/david_warner/436340581/

http://www.flickr.com/photos/david_warner/436340547/

http://www.flickr.com/photos/david_warner/436340908/

I'm hoping someone will tell me this is a simple fix. As my Cyrus is dearly loved :-(

Many thanks
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Old 28th March 2007, 11:11 AM   #2
Geoff is offline Geoff  United Kingdom
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From your photos it looks as though your Cyrus is one of the earlier versions (non-metalic case). Email me and I will send you a copy of the schematic from which you will be able to determine the relevant resistor values.

It is also likely that the output transistors, and possibly the driver transistors, have also blown so you will need to check these and replace them if necessary.
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Old 28th March 2007, 02:38 PM   #3
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Geoff

That sounds about right, Unfortunately I cant e-mail you until my account is out of moderation (not too long I hope)

Although I can solder it's been a long time, and I'm not really sure how to identify the parts of the circuit.

I was hoping to just replace the components that were visible burnt out.

Perhaps this might be a job for a profesional? Any ideas how much this would cost (just a ballpark figure would be fine)

As a sidenote, I damaged the Cyrus whilst trying to connect a mission subwoofer to the speaker outs - I have bi-wired speakers and the sub takes the signal direct from the speaker outs. After the thing blew I realised that I have the + and - of one of the bi-wire cables going into the same banna plug and something pretty similar at the other end going into the sub - silly I know, I was using flat QED cable and I got a bit confused with the labels. Do you think that would have created some kind of short?

Thanks again
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Old 28th March 2007, 02:55 PM   #4
Geoff is offline Geoff  United Kingdom
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Go to my website. My email address is on the home page. Unless things have changed recently, Cyrus will service and repair the amp but it will be expensive (it will probably cheaper to buy another working Cyrus 2 on eBay). I am happy to talk you through the process by email (or phone if necessary) if you want to give it a go yourself.
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Old 28th March 2007, 03:07 PM   #5
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Quote:
Originally posted by mannotanumber
After the thing blew I realised that I have the + and - of one of the bi-wire cables going into the same banna plug and something pretty similar at the other end going into the sub - silly I know, I was using flat QED cable and I got a bit confused with the labels. Do you think that would have created some kind of short?

Thanks again
Absolutely! In very simple terms: The amplifier is used to 'pushing' current through a resistance of ~ 4 to 8 Ohms speakers. This is something that the amplifier works against in normal operation. When you short the outputs you take away the thing that prevents too much current from flowing through the amplifier.
It is extremely likely that this has caused the output transistors (on the heatsink) to have blown and also taken out some surrounding components.

Your amplifier should also have some (better to do all) of the electrolytic capacitors changed as well due to the age of the amp. We have seen some around here that have gone. There's no point fixing it just to have it fail again due to age.

I have 2 Cyrus Ones with similar problems so I would appreciate you posting your results here if possible. I need a bit more confidence before I dive in to mine!!

Martin.
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Old 28th March 2007, 04:01 PM   #6
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Thanks for that,

The Caps look to be in very good condition. I got this unit on e-bay with a mission service sticker over it and I have a feeling some components have been replaced quite recently. If anyone knows where I could source any new caps, resistors etc then please let me know.

Is something Maplins can provide I've always found them to be very unhelpful.

Many thanks
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Old 28th March 2007, 07:22 PM   #7
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Hi,
It's interesting that it has a Mission service sticker. I wonder what they did. Must have been a few years ago though before Cyrus became a company in their own right (independent from Mission).

Changing the caps is worthwhile if only for long term reliability. For improvements in sound I heartily recommend changing the 2 large power supply smoothing caps and perhaps upping the capacitance a little. Cyrus one and two sound a little forward at the best of times but the bass can be strangled by these old caps. But, of course, you'll need to get it working first!

I'm on a very tight budget so I generally identify the bits and pieces that I need and then do a European search on Ebay. I wouldn't get output transistors from Ebay though due to the high number of counterfeits around.
I have bought some of the more exotic items from http://www.hificollective.co.uk/.
You could probably get most of the parts from Maplin and I'd be happy to help you find them. You may find it easier just to place one order with RS components ore Farnell or .......

I'll leave it up to Geoff to advise you on the replacement transistors this is where I get lost and that is why I still have two broken Cyrus amps!!

Martin.
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Old 28th March 2007, 08:08 PM   #8
Geoff is offline Geoff  United Kingdom
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Quote:
Originally posted by Sonusthree
I'll leave it up to Geoff to advise you on the replacement transistors this is where I get lost and that is why I still have two broken Cyrus amps!!
Martin

Replacement output transistors need not be all that expensive, particularly if you are willing to accept a substitute. When I ordered a replacement PT7 from Cyrus about ten years ago they sent a BUV28 which I could have bought at less than half the price elsewhere.

Grandata list the BUV28 at 1.10 but they do state in their terms and conditions that most of their stock is 'replacement parts' (second sourced?). Nikko has the BUV28 at 2.75 and the BUV28A at 2.19. Cricklewood list the BUV28A at 2.50.

If you are happy with a substitute, the MJE13009 looks a good match for the BUV28. Farnell have these at 1.33 (non-RoHS) or 1.91. They are also available from RS (1.64), Cricklewood (1.00), Nikko (0.82) and Grandata (1.00).

All of these are TO-220 and so will fit all Cyrus 1s and the earlier Cyrus 2s. If you have a v7 Cyrus 1 or 2, the STW13009 available from Farnell for 0.86 looks like it might be a good bet. It has a larger TO-247 case which means lower junction temperatures and so greater longevity and, IIRC, the SOA is better so there should be less risk of failure if the output is presented with a very low impedance load.

Another candidate in a larger package (TO-3P or TO-247 depending on manufacturer) is the BUV48/48A which last time I checked was significantly cheaper than the BUV28.

Please note that, as yet, I have not tried any of these alternatives to the BUV28 in one of my amps though I intend to do so in the not too distant future as one of them is currently running on some slow 2SD6xx devices.

Geoff
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Old 28th March 2007, 08:27 PM   #9
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Geoff

While your here I went to the farnel website to order the resistors 0.5W or 0.6W metal films for R84 but got stuck with the actual resistance rating that I need - I'm so sorry I cant work out how to determine this.

Thanks for you patience.

Dave
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Old 28th March 2007, 08:38 PM   #10
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Thanks Geoff, I don't want to hijack this thread but I suppose that it's relevant.

I have two broken Cyrus one amps. One plastic case neon logo and one rev 7. I'm especially interested in fixing the later model for bi-amping duties with my working Cyrus 2 (&PSX).

I bought both of these amps a long time ago very cheaply from Ebay and they both have one channel down. I tried to fix them a few years ago by substituting parts from one channel to another with no luck and, surprisingly, no further damage. I now know that this was a terrible idea!! I'd like to have a proper go at it now. The earlier model was occasionally being used to power a DIY guitar cabinet with it's remaining channel but unfortunately I knocked the case very lightly and saw a spark inside and then no sound!! It was the lightest of knocks.

What is the priority for testing for someone of my fairly limited experience? I know that I should check the output transistors and the surrounding resistors but what about all the small transistors. If I miss a dodgy one will all of my work be in vain? Is there a foolproof way to get it working?

I had considered a complete renewal of all the transistors and electrolytics. I want to keep these amps long term so don't mind the trouble and cost but can't afford to do it twice! The small transistors are many and quite expensive when added up.

My main issue is whether or not I can just substitute parts without re biasing anything. In an ideal world I would just change out all the transistors for recommended types and then relax.

Is it that easy or is it as hard as I have imagined?

My apologies to mannotanumber if I am getting in the way. I had considered starting a new thread but thought that we were essentially in the same situation.

Cheers,
Martin.
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