Bigal42

CMT-CP500MD Stuck in Standby Mode

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I have a CMT-CP500MD system which has decided to remain in Standby Mode. When I plug into mains I can see information on display as it displays the word Standby and also goes into Demonstration mode if I press Display on remote.

The backlight however does not come on and pressing standby button does not switch on device. I am loathe to get rid of the system if it is something relatively simple that can resolve the issue, Is there an internal fuse or something. If there is no solution then it's off to the Hifi graveyard in the sky.

Grateful for any support

Kind Regards

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maybe a worn out or defect fuse on the PSU ? Do you hear a clicking relais when you try to power on ?

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Yes. I can hear a slight click whilst pressing the power button. Is the PSU accessible?

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most likely it is not. In fact it is a real pain to open these mini systems. I´ve had trouble with several before :D

The PSU should be on the back of the Unit. IF it´s just a fuse that´s defect you could be lucky.

Did you try to reset as per manual ->

1 Disconnect the power cord from the wall outlet. 
   2 Reconnect the power cord to a wall outlet.
3 press Power
    4 Press TUNER BAND, CD EJECT and REC MODE at the same time.
     Look at the manual for failure codes @page 51 here ->http://pdf.crse.com/manuals/4233759133.pdf

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On 2016. december 2. at 6:15 PM, Bigal42 said:

When I plug into mains I can see information on display as it displays the word Standby and also goes into Demonstration mode if I press Display on remote.

The backlight however does not come on and pressing standby button does not switch on device.

 

On 2016. december 2. at 8:14 PM, Bigal42 said:

 I can hear a slight click whilst pressing the power button.

Do I understand it correctly: when plugged into mains, the display works (can play demo), also, the unit responds to the power button (switches the relay on). But then the unit does not come up into normal mode.

If this is the case, I am not sure it is just a fuse problem. The "power on" signal is handled by the main IC, and  that must have valid power rails to be able to sense the power button and to command the relay switching circuitry. Same for the display, the LCD controller must have proper power lines, to show anything on the display.

The two fuses protect the main transformer (plus there is a third one buried into the windings), and in case any of them was blown, neither the display nor the power button would work.

But my conclusion can be wrong, if the standby system is on a separate power circuit.

 

I suspect one of the internal devices (CD or MD) stopped responding to the main IC, that disables the whole system. Troubleshooting and repair is still possible, but it is very hard via the internet, it is better hands-on, with necessary test gear.

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Thanks NGY. I have removed the PSU and found that fuse F905 has blown. It is a 0.8A fuse that feeds the Main transformer. Not sure how much success I'll have but will give it a try.

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i just thought there was a seperated standbye circuit so if this was the Fuse for the mains  you could be lucky.

waiting for a good news :-)

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Ok All. Carried out a fuse change as planned and on switch on Back light came on momentarily then went off again. Performed the reset as mentioned above and when 3 buttons are pressed I hear  a click and when released I hear another click but no code displayed and no backlight. I've managed to check fuses again by only taking off side panel and F905 has blown again. Can't understand why this fuse keeps blowing and also which voltage is supplying power to display.

I have uploaded power Circuit Diagram

Any ideas??

Cct Diag.pdf

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Fuses blow for a reason. In this case, something is clearly dead. I'm not the guy to ask, NGY would have much clearer ideas exactly how this thing might have died. I'd guess one of the big capacitors. If you unload the PS by disconnecting whatever it's connected to you can check the assumption at the cost of another fuse. Don't even THINK about increasing the fuse thickness (rating). If it passes that test, then there is a dead short somewhere inside the CMT-CP500.

(edit) just a quick thought.... it WAS working for long period before? I noticed that this machine has lots of voltage options, and on some models a switch for 115-230 V. You don't say where you are in the world. Is it possible it's being plugged into the wrong mains voltage?

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Thanks sfbp. I'm in the UK using 240v and have never had cause to move voltage switch.

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Stephen summarized it very well, how to check the PSU board itself alone.

My thoughts (~blind assumptions):

- I would expect the PSU being fully OK without any boards/devices attached to it - see below why.

- F905 is on the primary side of the main transformer. It would blow when 1) there is a transient from the mains voltage, or 2) the primary windings of the mains transformer is burned into a short circuit (not very probable, for the thermal fuse buried into the primary windings), or 3) one of the secondary windings is burned into a short circuit (not very probable either), or 4) there is an overload/overcurrent appearing on the secondary side.

- the main transformer has two separate secondary windings. One is protected by two other fuses, F903 and F904. In case 4) above, I would expect one or both of those blow before the mains fuse would blow. This would conclude that all parts supplied from this voltage (+/- 14V and 8V) should be OK (from the power supply question's point of view).

- the other winding is not protected by any fuses interestingly. If we disregard  cases 1), 2) and 3) above, then I would suspect this part of the circuit having trouble. For one, as Stephen mentioned, the large cap(s). Next one: following the schematics, it shows that the power amplifier part is running on this voltage (+/- 22V). If one of the IC-s (IC101/IC201) is blown (i.e., their output transistors burnt thru, for a faulty speaker/cable, overdrive, or else - I have already seen similar cases), it can shortcut the power rail, and without any fuses on the secondary side, the primary side fuse should blow.

You may want to begin with the instructions of Stephen. (It may also help measuring the secondary voltages, to see everything is in order.) Once the PSU board is cleared, check the resistance between points 9-10 and 10-11 of the CNP307 connector on the main board. 

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Very good point - shorting the output of the speakers might do it. This is easily done, and easily rectified. But as Gyula says, one of the three transistors on the page you posted (Q901,902 or 903) may have failed. These are standard easily available parts (ie you do not and should not have to spend big bucks buying them from Sony).

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I can't hold my breath... Did you have time to look at it?

Before "it's off to the Hifi graveyard in the sky", I would be happy to give it a chance.

 

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