Hi,
I've a serious problem with a Cyrus PSX-R power supply, version 2, connected to my Cyrus III amp. This device normally is able to supply two regulated voltages (+35v and -35v) to a number of Cyrus amps.
The problem: increasing the amp volume, after a certain level the positive voltage progressively collapses to very low values and obviously the sound becomes awfully distorted, and even disappears. Instead, zero problems about the negative voltage. This happens only when the amp is connected to the loudspeakers: in other words, depending on the current request.
From what I've understood, a positive reference voltage (+3,5vdc) is submitted to a NE5534 op amps and here multiplied by 10, in order to keep a regulated output of
+35volt. This rate is in fact respected, as it's the positive +VREF that collapses first....
For information, the source rectified voltages to be regulated are +/- 48vdc, through a massive transformer. The output transistors are two parallel 2SD1047, driven by a MJE243/MJE253 couple
Any idea about the fault? How could I investigate furtherly?
Many thanks in advance to everyone
I've a serious problem with a Cyrus PSX-R power supply, version 2, connected to my Cyrus III amp. This device normally is able to supply two regulated voltages (+35v and -35v) to a number of Cyrus amps.
The problem: increasing the amp volume, after a certain level the positive voltage progressively collapses to very low values and obviously the sound becomes awfully distorted, and even disappears. Instead, zero problems about the negative voltage. This happens only when the amp is connected to the loudspeakers: in other words, depending on the current request.
From what I've understood, a positive reference voltage (+3,5vdc) is submitted to a NE5534 op amps and here multiplied by 10, in order to keep a regulated output of
+35volt. This rate is in fact respected, as it's the positive +VREF that collapses first....
For information, the source rectified voltages to be regulated are +/- 48vdc, through a massive transformer. The output transistors are two parallel 2SD1047, driven by a MJE243/MJE253 couple
Any idea about the fault? How could I investigate furtherly?
Many thanks in advance to everyone
Try to measure series pass transistors, mainly its hfe. Perhaps they are degraded and the can't give sufficient current to the load. I'm refering to T103/105/107 and 109. Please, during tests use a filament bulb in series to the mains to prevent future damage, and also use resistances of about the same load current capability as the normal load. If something goes wrong, it is better to discard a blown resistor over an amplifier entirely.
Also check capacitors in the rectifiers.
Also check capacitors in the rectifiers.
Hi Osvaldo,
I've already checked the junctions of those transistors, not their hfes. I will do!
Thanks a lot for your kind support
I've already checked the junctions of those transistors, not their hfes. I will do!
Thanks a lot for your kind support
Measure hFE. The junctions voltage (diode test) may measure good, but if the regulator isn't capable of mantain output voltage, may be a loss of gain or a premature action of the current limiter circuit around those output devices.
Hello Sorry for the automatic translation .....But I'm Italian from Venice....I recently bought a pair of Mission Cyrus two + PSX I noticed that in the cyrus two inside the R 121 section instead there are 2 resistors of only one as I usually see on sites where this amp is mentioned and I saw that the F4 fuse pair was not removed to pair the PSX, is my question normal? From the videos he sent me during the purchase we can see that the old owner had both 2 frames (Cyrus + PSX) with the power leds on, so he used the internal power supply of the Cyrus, I still ask if this is normal or damaged if not remove the F4 fuses inside the Cyrus using it in pairs Cyrus + PSX thanks I hope someone can help me Merry Christmas everyone
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Ciao scusa stavo dicendo che all'interno del cyrus due nella sezione R 121 ci sono 2 resistori invece di uno solo come vedo di solito. chiedo è normale o no?🙂😉
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My issue 7 board doesnt even have R121
