Cyrus Two V6 Phono Fault

Good evening guys.

I am hoping someone can help me with a problem?

On Wednesday I totally re-capped my old Cyrus 2 amp. What I did do is change all the caps for non polarized caps. Everything worked fine and sounded great. I then realized that some of the caps are polarized and wanting to keep the unit original I replaced the caps that should be polarized with the correct caps, paying attention to polarity. Since doing this the phono line has stopped working completely, all other inputs are fine. Please can someone guide me in the direction to diagnose the problem.

I am a novice in this area so any help is much appreciated. Thanks so much
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
First steps are to check the supplies to the phono stage. The circuit I have shows both dual and single opamps and so the positive supply pins differ for each. Pin 7 for the singles and pin 8 for the duals. Pin 4 is the same for both.

So measure the supplies on each opamp. You should see PLUS 18 on the positive supply and MINUS 18 for the negative.

Next look at the output pins of each opamp. They should all read very close to zero volts DC.
 

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First steps are to check the supplies to the phono stage. The circuit I have shows both dual and single opamps and so the positive supply pins differ for each. Pin 7 for the singles and pin 8 for the duals. Pin 4 is the same for both.

So measure the supplies on each opamp. You should see PLUS 18 on the positive supply and MINUS 18 for the negative.

Next look at the output pins of each opamp. They should all read very close to zero volts DC.

Thanks Mooly, could you advise how to test and at which points please, I have a multimeter
 
Surely making mistakes is what does damage - failing caps can damage other parts, new caps should be good for a few decades. Replacing lots of caps is often tricky work and involves significant disruption to an amplifier, so care is needed to restore and replace all the connections/connectors and ensure they are solid as well as getting the caps replaced right.


Unfortunately electrolytics are effectively consumables, even the best, though it is wise to assess the state before committing to a full recap. Filter caps often see significantly more temperature than other caps due to high ripple and are the first suspects to test and perhaps replace. If an amp has seen 20 years hard duty at high temps you should assume all the caps are aging, if its only seen very light use they may be good for another few decades...


Failing to recap can lead to oscillation in solid state amps, which can be destructive to amp and speakers.
 
Thanks guys.

This is where I’m at: I hadn’t realized when testing opamp that I should of been testing for ac, I have tested now but can someone confirm I’m doing it correctly, I placed black probe on neutral of PSX input and red on pins as recommended above, is the the correct method and if so I am getting 0 voltage, please can anyone advise where to go next.

Thanks so much
 

as_audio

Member
2008-05-13 6:18 pm
MT : in Cyrus 2 only four caps need to be checked even after decades of hard use.

JH : black wire of your multimeter goes from MM "Com" to black speaker terminal
of amp. Address test points with the red wire. I assume this is a Digital MM.

Check for dc voltage, because positive phono supply is missing if you only
see negative voltages here.
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
Thanks guys.

This is where I’m at: I hadn’t realized when testing opamp that I should of been testing for ac, I have tested now but can someone confirm I’m doing it correctly, I placed black probe on neutral of PSX input and red on pins as recommended above, is the the correct method and if so I am getting 0 voltage, please can anyone advise where to go next.

Thanks so much

You are measuring DC voltages in the power supply, not AC.

Place the black meter lead on ground and measure the DC voltage on the appropriate pins.

The parts lists mentions NE5534 opamps. Those are singles and so you should have plus 18 volts on pin 7 of each one and minus 18v on pin 4 of each.

The LF353 are dual opamps and while pin 4 remains the same, the positive is now on pin 8.

The output pin of each opamp should be zero volts DC. That is pin 6 for the NE5534 and pins 1 and 7 for the LF353.

In the power supply you need to check the two supplies here. Look for plus 18 at the top and minus 18 at the bottom.
 

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