Hello all hope I'm placing this in the correct place but I need help!!I have a Cyrus 2 and when I turn on I get a large bong noise out of both speakers!! I have changed a few small caps but nothing! Still sounds fab but obviously not good for speakers on start up as I've had my meter on speaker terminals and dc comes through but then settles to zero after about 15 seconds.
once the amplifer has made this noise you can flick the amp off and back on and no noise but this is because I guess that it already all powered up still inside ? Please help and any suggestions welcome. I have tryed swapping the main caps and still the noise drives me crazy!!! I dont want to use it till i get ir sorted i dont want to damage my speakers!! That would just send me over the edge!😱 I use a psx with this and still does the noise when i use psx!
HHHHHHHHHHHEEEEELLLLLLLPPPPPPPPPP.
once the amplifer has made this noise you can flick the amp off and back on and no noise but this is because I guess that it already all powered up still inside ? Please help and any suggestions welcome. I have tryed swapping the main caps and still the noise drives me crazy!!! I dont want to use it till i get ir sorted i dont want to damage my speakers!! That would just send me over the edge!😱 I use a psx with this and still does the noise when i use psx!
HHHHHHHHHHHEEEEELLLLLLLPPPPPPPPPP.
Assuming it's the Issue 7 version with toggle switch. C43 470uF may be taking too long to charge due to old age. On the other channel I think it's C143.
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Hi thanks for reply. Yes it's the toggle version,and the caps you are talking about 470uf 6v position c43 and c44 . Yes I have changed these and have also changed c67 c68 and also c53 c54 c55 c56 !! All the obvious has been changed and that's me I'm up against a wall and I don't give up this easy . Any more ideas??? Cheers
Check the bias current at the left and right bias test points. It should be 8-20mV. If not then adjust to 8mV.
Bias current won't cause pops at turn-on, and there is no way to "adjust" it without swapping resistors.
Check that R51 and R71 are good and connected properly.
Are both channels behaving the same? Did anything happen that may cause it, e.g. you unplugged or plugged a connection?
Check that R51 and R71 are good and connected properly.
Are both channels behaving the same? Did anything happen that may cause it, e.g. you unplugged or plugged a connection?
Thanks will check later. The two pins for bias testing are under ribbon cable 2 for each channel I guess? And I just put my multi meter across each set of pins per channel? I assume this is correct. I wil be back with readings later. Don't know how to adjust bias if incorrect!!(but I'm sure someone does) 🙂
You adjust the bias current using the 2 pots on the board.
If you agree to upload it somewhere and link it to this thread, I have the service manual and schematics for this amplifier. Give me an email if so.
If you agree to upload it somewhere and link it to this thread, I have the service manual and schematics for this amplifier. Give me an email if so.
Have checked the bias test points. they are readind very high.
Left channel 129mv
right channel 131mv
so they are both very similar.
The cyrus does not have bias pots for adjusment so what to do next??
I assume the noise on start up is the bias is to high then??
Please advice .
I really appreciate your help.
Left channel 129mv
right channel 131mv
so they are both very similar.
The cyrus does not have bias pots for adjusment so what to do next??
I assume the noise on start up is the bias is to high then??
Please advice .
I really appreciate your help.
I also have the service manual 🙂 and have worked on these amps before.
The issue 7 "toggle" version does not have bias pots. It used fixed resistors.
The issue 7 "toggle" version does not have bias pots. It used fixed resistors.
I've got them too, it took me three seconds to download them from HiFi Engine | Download Free User/ Service Manuals, Amplifier, Receiver, CD, Tape, Tuner, Video
wasnt checking the correct place or bias. the big white resisters.
they are reading 2.5mv so according to schematic im going with 220 resisters over to metal pillors under ribbon cable to increasd bias. See if this works!!!
Ill be back.!
they are reading 2.5mv so according to schematic im going with 220 resisters over to metal pillors under ribbon cable to increasd bias. See if this works!!!
Ill be back.!
Well I used a 220r resistor across solder pillars and then turned on amp. Checked bias and it was rocketing up going above 100mv and rising so I turned amp of!! Could fell the heat coming from transistors!! And still the bong noise on start up. What to do next ??? I'm stumped again!!!
I will not be defeated !!! Help!!!!'
I will not be defeated !!! Help!!!!'
You shouldn't have soldered anything there, it is a test point to measure with a volt meter. I still think checking the bias current is barking up the wrong tree. Your previous reading of approx 130mV indicates approx 300mA bias, which is too high. However, both channels are consistent.
Have you checked R51 and R71 yet? Also, any comment on what may have caused the problem?
Have you checked R51 and R71 yet? Also, any comment on what may have caused the problem?
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Hi richie i have now checked resistors (on the board) and the results are as followed
position r51 55k
position r71 74.5
having looked at the schematic the said resistors should be 75k but r51 is not reading this,but is this because its still in circuit???😕
Go easy on me im trying my hardest here, im a builder by trade so all this electrical jiggery is quite new to me but im finding it very interesting and i hope very rewarding when i have fixed this amplifier!! I HOPE!!!:
THANKS FOR PATIENCE
position r51 55k
position r71 74.5
having looked at the schematic the said resistors should be 75k but r51 is not reading this,but is this because its still in circuit???😕
Go easy on me im trying my hardest here, im a builder by trade so all this electrical jiggery is quite new to me but im finding it very interesting and i hope very rewarding when i have fixed this amplifier!! I HOPE!!!:
THANKS FOR PATIENCE
R51 has a bigger capacitor across it which will give a reduced reading, so I think what you have is fine.
Now I see that you measured 2.5mV across the big white resistors R107, well this shows the bias current to be approx 57mA which is perfect.
Please can you confirm if the amp just started behaving this way or if something was unplugged etc and it started doing it.
Now I see that you measured 2.5mV across the big white resistors R107, well this shows the bias current to be approx 57mA which is perfect.
Please can you confirm if the amp just started behaving this way or if something was unplugged etc and it started doing it.
This was my dads Amplifier so I don't know what happened to it. Not been used for around 5 yrs. this is why I am determined to fix it . So sorry no history to help!!!
What's next to check
What's next to check
Is there any noise or cone movement when you turn it off? I seem to recall even a good working Cyrus 2 Issue 7 amp has some turn on noise/thump - the question is how bad is it and is yours worse than normal.
Since this is it an old power amplifier you should check the power supplies voltages for ripples. Read all voltages with the voltmeter selector switch in AC. All voltages should read less than .5 volts. Hold the probes until you can see the reading it is stable. It is time when reading DC in AC.
The turn on noise is quite bad and defiantly not correct. No noise when turn of,
But after doing more probing with my multi meter I have found something!!!!! I think.
Position vr1 transistor 8930 (lm337t) is reading 18v from out pin right side
Vr2 8948 (lm317t) is reading 7.2 on the out pin middle. This should also be 18v but is not!!!
Have I found something here???????? When reading the transistors I'm grounding the neg to chassis and pos to pin I'm assuming this is correct.
But after doing more probing with my multi meter I have found something!!!!! I think.
Position vr1 transistor 8930 (lm337t) is reading 18v from out pin right side
Vr2 8948 (lm317t) is reading 7.2 on the out pin middle. This should also be 18v but is not!!!
Have I found something here???????? When reading the transistors I'm grounding the neg to chassis and pos to pin I'm assuming this is correct.