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cyrus 1 output transistor question. push-pull?
cyrus 1 output transistor question. push-pull?
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Old 9th December 2017, 05:14 PM   #1
randombeliefs is offline randombeliefs  United Kingdom
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Default cyrus 1 output transistor question. push-pull?

Hi all

I fixed my brother's mission cyrus two for him recently (pre amp power supply circuit track fault and a sulphided selector switch. He now thinks I'll be able to fix his daughter's cyrus one.

that's a bit sicker though.

when i plugged it in one of these white things glowed red and started smoking.

I assume this isn't good and unplugged.

So I'm guessing (wildly, cos I'm not knowledgeable) that a transistor has gone open and too much current ran through the white thing ?

<a href="https://ibb.co/mtvZVG"><img src="https://thumb.ibb.co/mtvZVG/20171209_174840.jpg" alt="20171209_174840" border="0"></a>

I thought I'd replace the white thing, and all 4 output transistors but they all have the same marking on them (C8837 CYRUS PT7) and i expected each channel to have a pnp and an npn ? Im also guessing they aren't made by mission and are obsolete.

could they be different but have the same code marked on them ?

can i test them with a multimeter or will that not work cos of failure ?

I could do with knowing what to order.

thanks for any help
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Old 9th December 2017, 05:38 PM   #2
rayma is offline rayma  United States
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Quote:
Originally Posted by randombeliefs View Post
I thought I'd replace the white thing, and all 4 output transistors but they all have
the same marking on them (C8837 CYRUS PT7) and i expected each channel to have a pnp and an npn ?
Many amplifiers are "quasi-complementary", using all the same output device for both polarities.
This amp uses all identical outputs, with paralleled pairs for each polarity for each channel.
There's probably more wrong than just those, like the emitter resistors and driver transistors.
Cyrus 2 - Manual - Stereo Integrated Amplifier - HiFi Engine

Last edited by rayma; 9th December 2017 at 05:44 PM.
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Old 9th December 2017, 05:42 PM   #3
Mooly is offline Mooly  United Kingdom
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cyrus 1 output transistor question. push-pull?
If the output transistors are all the same then the output stage will be a 'quasi complementary' type, probably using NPN devices. These were quite common.

Not familiar with the C8837 but transistors marked Axxxx Bxxxx Cxxxx and Dxxxx usually refer to the JIS marking system. See 6.1 here:

Transistor - Wikipedia)

The mission might be outside your comfort zone to work on. The resistors (white thing ) will need replacing along with any failed semiconductors and the unit given a thorough inspection for dry joints and other possible problems.

Edit... service manual is available here:
Cyrus 1 - Manual - Stereo Integrated Amplifier - HiFi Engine

It is a Quasi design, two NPN's.
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Old 9th December 2017, 05:45 PM   #4
richie00boy is offline richie00boy  United Kingdom
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cyrus 1 output transistor question. push-pull?
They are all npn because it's a quasi complementary output stage. You will need driver transistors as well.

One or more likely both output transistors have blown. The drivers usually get damaged as a consequence. The white thing that got hot is a dual resistor.
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Old 9th December 2017, 05:55 PM   #5
randombeliefs is offline randombeliefs  United Kingdom
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thanks very much. could you help me locate the driver transistors ? there are two little transistors between each output pair and they have a kind of heatsink connection to the output ones. or could they be thermistors or something ?

the white thing says
RGC33
0.220KX2
NOBLE U88

off to google that ...

thanks for the manual link too. half a chance of locating the duff bits.
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Old 9th December 2017, 06:08 PM   #6
amptech is offline amptech  Scotland
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Quote:
Originally Posted by randombeliefs View Post
Hi all

I fixed my brother's mission cyrus two for him recently (pre amp power supply circuit track fault and a sulphided selector switch. He now thinks I'll be able to fix his daughter's cyrus one.

that's a bit sicker though.

when i plugged it in one of these white things glowed red and started smoking.

I assume this isn't good and unplugged.

So I'm guessing (wildly, cos I'm not knowledgeable) that a transistor has gone open and too much current ran through the white thing ?

<a href="https://ibb.co/mtvZVG"><img src="https://thumb.ibb.co/mtvZVG/20171209_174840.jpg" alt="20171209_174840" border="0"></a>

I thought I'd replace the white thing, and all 4 output transistors but they all have the same marking on them (C8837 CYRUS PT7) and i expected each channel to have a pnp and an npn ? Im also guessing they aren't made by mission and are obsolete.

could they be different but have the same code marked on them ?

can i test them with a multimeter or will that not work cos of failure ?

I could do with knowing what to order.

thanks for any help

Hello, I would say read up on amplifiers on how they work etc before warming up the solding iron as a little understanding could make things even sicker!

Plus looking on here for the answers may confuse you a little regarding terms such tail pairs/ vas stages etc.

Hope all goes well.
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Old 9th December 2017, 06:44 PM   #7
randombeliefs is offline randombeliefs  United Kingdom
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far enough thanks I'll go learn
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Old 9th December 2017, 06:46 PM   #8
randombeliefs is offline randombeliefs  United Kingdom
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Quote:
Originally Posted by richie00boy View Post
They are all npn because it's a quasi complementary output stage. You will need driver transistors as well.

One or more likely both output transistors have blown. The drivers usually get damaged as a consequence. The white thing that got hot is a dual resistor.
thank you !
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Old 9th December 2017, 06:47 PM   #9
randombeliefs is offline randombeliefs  United Kingdom
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Quote:
Originally Posted by amptech View Post
Hello, I would say read up on amplifiers on how they work etc before warming up the solding iron as a little understanding could make things even sicker!

Plus looking on here for the answers may confuse you a little regarding terms such tail pairs/ vas stages etc.

Hope all goes well.
thanks very much. i am trying to learn but it's hard to know where to start and at what point you know enough to have a go
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Old 9th December 2017, 07:00 PM   #10
Mooly is offline Mooly  United Kingdom
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cyrus 1 output transistor question. push-pull?
There are a couple of variations of this amplifier in the service manual although both are basically the same configuration details.

You need to be confident in fitting replacement transistors, probably of a different type to the original parts. Also as a general rule, avoid buying semiconductors from well known auction sites, there are just far to many fakes and remarked devices around.
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