my Cyrus 1 history

jamal

Member
2010-09-20 1:53 pm
hi, I bought a Cyrus 1 in the 80's. just after the warranty the transformer when bad and I bought a replacement. in the 2nd year the selector switch got problem. actually alot of dirt have went into the selector switch. so I take it out and soak in a cleaning solution. After soldering it back, I cover it with some electric tape also the volume and balance control. take note, till today the problem did'nt show up again.

after 10 years of service the output transistor when bad. I repair it. it work fine till today. last week I change all the electolytic capacitor and the diodes. the rectifier diode were upgrade to 6A type. but I can't get the 470uf non polarise capacitor. still looking a around for it.
also upgrade the reservoir capacitor to 10000uf. I change all the RCA or so call phone socket to gold plated version. I drill a bigger holes so that all the RCA can fit in. The speaker output were also upgrade to gold plate version.
now I am enjoying the fruit of my labour:D
 

jamal

Member
2010-09-20 1:53 pm
my_cyrus.jpg
 
Yah the Cyrus is by far the best cheap amp out there "walking the dog" on amp 20 times the price. That NP 470µF you are looking for... you could use a Nichicon Muse or I just used a regular Panasonic FM because the DC there is only about 120mV. All aluminum electrolytic capacitors are non-polar up to something just over a volt. Would have to look up the exact voltage but with the low DC found there a polar works fine..

Best of luck!
 

jamal

Member
2010-09-20 1:53 pm
hi thanks, the cyrus 2 with basically the same circuit ,did not have the 470uf 6v capacitor as the Cyrus 1. that drawing is issue 2006. but some friends did reported here in this forum that their Cyrus 2 indeed was install with 470uf 6v non polar capacitor. now I am bit confuse. I think it will work fine without the capacitor. as reported in this forum, putting a polar cap ,will cause the cap to go hot, coincidentally ,I have gone thru many amplifier circuits. none of them utilize such a high value of 470uf in their feedback path. May be this is the reason Cyrus remove the cap on issue 2006 onward. just a guess.

Yah the Cyrus is by far the best cheap amp out there "walking the dog" on amp 20 times the price. That NP 470µF you are looking for... you could use a Nichicon Muse or I just used a regular Panasonic FM because the DC there is only about 120mV. All aluminum electrolytic capacitors are non-polar up to something just over a volt. Would have to look up the exact voltage but with the low DC found there a polar works fine..

Best of luck!
 
I fixed one and replaced the NP with the one mentioned and no the cap did not get hot or show any other problem and worked and sounded fine. If the cap gets hot then there is something else wrong with the amp. Hot cap means more than the 120mV there (or oscillation) which means there is a balance problem in the amp which also needs fixed. Seems to me if the cap gets hot then blaming the cap for the problem still does not fix the real problem with the amp.
 
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jamal

Member
2010-09-20 1:53 pm
I have no problem with the cap. I just wanna change cos it is old. it were reported by a guy here in this forum that the cap get hot. btw if polar cap work fine, why do Cyrus take the trouble to put a expensive non-polar cap in the first pace?:D
 

Sherloq

Member
2009-10-26 1:30 pm
Hi guys, this seems to be the most up to date Cyrus One post around so thought I'd ask a quick one here:

Basically my quick blow fuses went a couple of weeks ago, and after identifying the dead transistors I worked back to find that pretty much everything past the Q31/Q33 drivers was pretty much gone. So i'm now in the process of replacing the transistors and the resistors inbetween. I've came to a bit of a confusing section in the user manual: The schematic shows R93, R95 and R97 as being 100ohm resistors - but the parts list shows them as 120R. The ones currently installed are 100 ohm from the color bands and doing some tests on the working ones. So what should I replace them with 100R or 120R?

Thanks for the help!
 

Sherloq

Member
2009-10-26 1:30 pm
Thanks for that. As to the cause... well I don't know for sure, but there seems to have been a short at the output stage (no physical evidence of overheating - although the amp often stays on for longer periods of time I dont push it too hard). I've identified the problem area as being after the Q31 and Q33 drivers and before Q35 and Q37 transistors as everything before and after that seems to be normal.

There maybe a chance that someone can help identify the problem, these are all the components I found need replacement:
R89, R93, R97, R101, R102, R103, R104, D3, D4, D5, D7 and of course Q41 and Q43.

Given this, are there any other parts of the board I should be devoting more attention to in search of problems?

Thanks
 

jamal

Member
2010-09-20 1:53 pm
my Cyrus 1 amp R93, R95 and R97 as being 100ohm resistors.
also try to change D3 & D4 to transdiode instead of IN4002. use the MJE253 PNP transistor as a diode for D3 & D4. it costly but it said that the transistor got a liner curve than a diode. hence a better symmetry waveform.

Hi guys, this seems to be the most up to date Cyrus One post around so thought I'd ask a quick one here:

Basically my quick blow fuses went a couple of weeks ago, and after identifying the dead transistors I worked back to find that pretty much everything past the Q31/Q33 drivers was pretty much gone. So i'm now in the process of replacing the transistors and the resistors inbetween. I've came to a bit of a confusing section in the user manual: The schematic shows R93, R95 and R97 as being 100ohm resistors - but the parts list shows them as 120R. The ones currently installed are 100 ohm from the color bands and doing some tests on the working ones. So what should I replace them with 100R or 120R?

Thanks for the help!
 
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Sherloq

Member
2009-10-26 1:30 pm
Thanks Jamal! I've actually got a few spare MJE253's I can use! How can I apply these should I disregard the base and use the emitter and collector as the anode and cathode?

I've also been doing a bit more testing and found the C53/C55 capacitors to be working OK - so still uncertain as to the cause of the short.

Another thing I failed to mention is that this happen after I opened up my cyrus to give the pots a clean as the inputs (with the exception of phono and cd) were not working properly and crackling a lot - any clues there?
 

Sherloq

Member
2009-10-26 1:30 pm
Me again... I think I've rationalised this through... Since MJE253's are PNP by shorting the base and the collector they would become the N-Type property from the base, whilst the emitter would stay as P-type. And therefore applied with the base-collector as the cathode (-) and the emitter as anode (+):

I would appreciate confirmation as I am no expert!
 
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jamal

Member
2010-09-20 1:53 pm
Sherlog, yes correct. short the MJE253 base and collector to form a diode.
regarding your noise pot, wrap up electric tape on the pot after cleanning (see pic on page 1). if not every few month you have to clean up the pot again. cause of short on my amp are usually surge current. do not ON the main while the amp power switch is on. after you on the main, wait for few seconds for all the capactor to charge up then only you can ON the amp main switch. also before you plug in the main power, make sure the amp pwr switch is OFF>

Thanks Jamal! I've actually got a few spare MJE253's I can use! How can I apply these should I disregard the base and use the emitter and collector as the anode and cathode?

I've also been doing a bit more testing and found the C53/C55 capacitors to be working OK - so still uncertain as to the cause of the short.

Another thing I failed to mention is that this happen after I opened up my cyrus to give the pots a clean as the inputs (with the exception of phono and cd) were not working properly and crackling a lot - any clues there?
 

Sherloq

Member
2009-10-26 1:30 pm
Hi Jamal, unfortunately I've had no luck with my power amp section yet...

I'm always very careful with turning the amp and power supply on - but your above point is very valid as the pre-amp section is constantly being powered by the mains (even when the amp switch is off). So it is very important to bring it up as you describe.

I seem to have narrowed the problem down to those exact transdiodes (D3 and D4), the power transistors (Q41/Q43) and the resistors that follow them (R101/R103 and R102/R104). These are all the components that failed this time - and I suspect the short should be around here somewhere! I'm going to give this one last shot before I lose my mind on this amp and go luck for a replacement (already thinking pioneer A400 or an older Marantz KI sig).
 

jamal

Member
2010-09-20 1:53 pm
these are common fault, usually these are the component that die together. mine you those are fuseable resistor. it is design to blow should anyting goes wrong. after replacing the components. Before you power up the amp, do a resistance check and compare the right channel with left channel. you know what to do if both reading differ.
 

jamal

Member
2010-09-20 1:53 pm
if you run out of ideas. just take out those transistors from driver to output and check for leakage. or you may have drop a solder lead on the board accidently. solder splash as they called it. pig tail short, while handeling the board you may touch a component lead that introduce a short. if you proceed on the board if a mine set of "every thing is ok" you can't locate the fault.