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
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
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
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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.
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.
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.
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.
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
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.
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.
thanks for the tip
i was looking at maplin Farnell and RS components.
can transistors just fail due to age or is there likely to be another underlying cause and the transistors failed as a consequence?
Hmmm... transistors don't wear out as such, and don't age as such but it is a fact that certain devices of a certain age (and from certain manufacturers) do suffer problems and unusual failure modes. There are no hard and fast rules on that, but I found as a service tech you did get a second sense when faced with these things.
RS, Farnell and CPC are probably the best suppliers in the UK as a generalisation. CPC is part of Farnell.
RS, Farnell and CPC are probably the best suppliers in the UK as a generalisation. CPC is part of Farnell.
what's would cause it to go wrong if not a transistor failure do other bits die of old age ?
Hello there,
Most of us here have been in the service trade for many a year and getting started on such topics can cost a high price if things go wrong plus you get zapped along the way!
Basic ohms law help's with working out volts current and resistances. Followed by test equipment use, meters for checking and how to carry out live testing.
Try a small chip amplifier ie tda2030 this gives 10 to 18 watts and very easy to build.
There are plenty of audio file books or even on line info and remember electrical saftey at all times.
Good luck with things
I would prefer he send it to ARS for a full service personally, but he can't afford to. Basically if i can't fix it she just has to do without. Which is looking likely ! reading up as best I can ...