Mission Cambridge
Hi Lohk,
The switch works OK .
Thank you very much.
Unfortunately .........another issue appeared - the power board .
Ther is a strong pressure on one of the bass drivers left channel at medium to high levels.
The amplifier cannot be used in this condition.
Initially I thought to replace ALL transistors except for the power ones but eventually decided to bring the amplifier to a service.
The guy who once had repaired a Cyrus 1 initially gave the opinion that it is a power transistor that failed.
Hopefully it is not as I even don't know what transistors they have used.
They are not marked.
Will know how it goes in the next week and report here.
Best regards,
Aleko
Hi Lohk,
The switch works OK .
Thank you very much.
Unfortunately .........another issue appeared - the power board .
Ther is a strong pressure on one of the bass drivers left channel at medium to high levels.
The amplifier cannot be used in this condition.
Initially I thought to replace ALL transistors except for the power ones but eventually decided to bring the amplifier to a service.
The guy who once had repaired a Cyrus 1 initially gave the opinion that it is a power transistor that failed.
Hopefully it is not as I even don't know what transistors they have used.
They are not marked.
Will know how it goes in the next week and report here.
Best regards,
Aleko
aleko,
if a power transitor has failed you will hear a strong distortion at every level. Or your fuses will blow immediatly. There is alson a chance that the driver transistors have failed (Q33, 37, 38, 34). I have repaired many of those Cyrus amps (way back in the 80ies) and these were the failures in 90% of them.
I think you can measure the transistors in situ, they are all NPN and should behave more or less the same. To be sure you have to look at the output waveform with a signal generator and a scope, but I fear you do not have one, otherwise you would have done that anyway. It is difficult to help if I have no more detailled infos.
The power transistors are custom made for these amps and should be still availlable form the company. What size are yours (depending on the age of the amp): TO220 or TO247?
if a power transitor has failed you will hear a strong distortion at every level. Or your fuses will blow immediatly. There is alson a chance that the driver transistors have failed (Q33, 37, 38, 34). I have repaired many of those Cyrus amps (way back in the 80ies) and these were the failures in 90% of them.
I think you can measure the transistors in situ, they are all NPN and should behave more or less the same. To be sure you have to look at the output waveform with a signal generator and a scope, but I fear you do not have one, otherwise you would have done that anyway. It is difficult to help if I have no more detailled infos.
The power transistors are custom made for these amps and should be still availlable form the company. What size are yours (depending on the age of the amp): TO220 or TO247?
Mission Cambridge amplifier - power amplifier module
Hi Alohka,
Thank you for the information and the circuit diagram of Cyrus 1 amp.
Please note that my amplifier is Mission Cambridge.
It is a different amplifier to the Cyrus 1 .
Today the power transistors of the bad channel have been checked ok.
The guy at the service said that the rest of the transistors also checked OK.
However he is unable to repair the amplifier .
He is giving up.
The reason is that there is a problem with a resistor (and yes - it smelled at home) .
I am taking the amplifier back home tomorrow .
Sent an e-mail to service@cyrusaudio.com asking them for circuit diagram and parts .
Will see how it goes .
The transistors up to the power ones are available.
I may need to measure all of the resistors of the good channel and make a diagram .
Then to replace the transistors in the bad channel or in both channels.
I have no clue what to do exactly to speed this up.
Best regards,
Aleko
Hi Alohka,
Thank you for the information and the circuit diagram of Cyrus 1 amp.
Please note that my amplifier is Mission Cambridge.
It is a different amplifier to the Cyrus 1 .
Today the power transistors of the bad channel have been checked ok.
The guy at the service said that the rest of the transistors also checked OK.
However he is unable to repair the amplifier .
He is giving up.
The reason is that there is a problem with a resistor (and yes - it smelled at home) .
I am taking the amplifier back home tomorrow .
Sent an e-mail to service@cyrusaudio.com asking them for circuit diagram and parts .
Will see how it goes .
The transistors up to the power ones are available.
I may need to measure all of the resistors of the good channel and make a diagram .
Then to replace the transistors in the bad channel or in both channels.
I have no clue what to do exactly to speed this up.
Best regards,
Aleko
Aleko,
it's the same amp - there is no difference - differences exist maybe in the age of the amp, there were of course slightly different models over the years. Did you specify your amp exactly yet?
If a resistor is "smelling" that means that it is getting hot because the currants went off a lot. It is very likely the a transistor is faulty (and maybe also the resistor already).
I would like to help you more but I need much more information:
Which resistor gets hot?
Do you measure an output CD offset? (the "strong pressure" maybe...)
Did you or your technician measure the driver transistors?
alohka
...everything can be repaired... but we should be careful with the planet...
it's the same amp - there is no difference - differences exist maybe in the age of the amp, there were of course slightly different models over the years. Did you specify your amp exactly yet?
If a resistor is "smelling" that means that it is getting hot because the currants went off a lot. It is very likely the a transistor is faulty (and maybe also the resistor already).
I would like to help you more but I need much more information:
Which resistor gets hot?
Do you measure an output CD offset? (the "strong pressure" maybe...)
Did you or your technician measure the driver transistors?
alohka
...everything can be repaired... but we should be careful with the planet...
Well, in December 2000 I bought (from cyrus in UK) 4 final stage output transistors for my amp, so I would have them reserved in case I ever needed them. At first they sent me two PT7 (TO220) transistors by mistake (I have a cyrus two - wich needs PT77 not PT7) however I got two bags (of matched pairs?) of transistor couples NOT MARKED PT7 but marked BUV28. after talking to them the technical department told me these are the correct transistors but I need PT77 (TO247). and they asked me to send them back so they can replace them. I did, and got two bags (again, matched pairs? I don't know?) of BUV48A.
As lohk said, all transistors were from ST.
This confirms the final stage being regular BUV28, relabeled (maybe matched).
As lohk said, all transistors were from ST.
This confirms the final stage being regular BUV28, relabeled (maybe matched).
Mission Cambridge
Hi Lohk,
I had specified the amplifier - yes.
In fact this appeared to be Mission amplifier and not Cyrus amplifier.
Anyway, need transistors ST 646 x 5 and 666 x 5.
These are the driver stage transistors for the right channel.
The left channel is OK.
The selector switch you sent appeared to be higher than the original .
It short circuited the power amp board.
Strangely enough what got damaged is the other channel...
The resistors almost burnt ( I had no fuses in the power supply!!!).
I will supply good resistors from Parts Connexion .
But the ST bipolar small signal transistors are not available.
Then do I need to know if they are PNP or NPN ?
How do I find an indication ?
Can you supply those transistors?
Or do you know wherefrom I can supply them?
Couldn't find them at the Mouser Electronics web shop.
Thank you
Best regards,
Aleko
Hi Lohk,
I had specified the amplifier - yes.
In fact this appeared to be Mission amplifier and not Cyrus amplifier.
Anyway, need transistors ST 646 x 5 and 666 x 5.
These are the driver stage transistors for the right channel.
The left channel is OK.
The selector switch you sent appeared to be higher than the original .
It short circuited the power amp board.
Strangely enough what got damaged is the other channel...
The resistors almost burnt ( I had no fuses in the power supply!!!).
I will supply good resistors from Parts Connexion .
But the ST bipolar small signal transistors are not available.
Then do I need to know if they are PNP or NPN ?
How do I find an indication ?
Can you supply those transistors?
Or do you know wherefrom I can supply them?
Couldn't find them at the Mouser Electronics web shop.
Thank you
Best regards,
Aleko
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Did you specify your amp as a Mission 778 somewhere? If this is your amp, I have very little information about it.
What has happened? The power amp cannot be shorted by the input switch (the power stage was not even activated). So something was fully wrong, which is beyond my imagination. I have no idea how I can help you here. Can you post close-up images of the pcb on both sides and post what exactly you have done?
I also have no idea which transistor you mean - I have never heard about the mentioned ones. The earlier Cyrus amps use ZTX753/653 for drivers, later MJE243 / MJE253, as far as I remember.
I am very sorry that my support created more trouble. But if you have soldered the switch into the amp without checking it and all possible connections and problems it is not my responsibility.
Klaus
What has happened? The power amp cannot be shorted by the input switch (the power stage was not even activated). So something was fully wrong, which is beyond my imagination. I have no idea how I can help you here. Can you post close-up images of the pcb on both sides and post what exactly you have done?
I also have no idea which transistor you mean - I have never heard about the mentioned ones. The earlier Cyrus amps use ZTX753/653 for drivers, later MJE243 / MJE253, as far as I remember.
I am very sorry that my support created more trouble. But if you have soldered the switch into the amp without checking it and all possible connections and problems it is not my responsibility.
Klaus
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