Cambridge Audio 840c Transport Mechanism Failiure?

[daws0n]

Today I picked up a used Cambridge Audio 840c for my dad, wired it up and it is not working properly.

Powers up OK, but the drive tray is making a loud whirring noise and refuses to stay closed (it keeps opening over and over).

I have made some videos using my digital camera:

http://dawsonspace.webspace.virginmedia.com/cdp1.AVI

^^As you can see if refuses to play any discs and keeps spitting the tray out every time with a loud whirring noise

http://dawsonspace.webspace.virginmedia.com/cdp2.AVI

^^I then made another video as the noise does not stop when the unit is powered off, it's like something is jammed? I have to force the power off using the switch on the back, but as soon as I power on again the tray ejects without intervention and it makes the same whirring noise.

It is working fine as a DAC via the digital input, so all in not lost... I have found that if you set it to "input 1" the CD tray does not engage on startup so does not eject automatically. However, the same buzzing/whirring noise appears when you attempt to turn it off. So, on top of refusing to play dics everytime it's shut off it needs to be shut off via the mains switch to stop the noise.

I can't complain for the price I paid but ideally he would like to play CDs so that it can replace his current player altogether (rather thn keeping it as a transport).

The seller seems genuine and assures me it worked ok yesterday so it seems that the fault has arisen during transport somehow... Can anyone please advice? He's offered to accept a return but I am tempted to open to it up and see what is going on, I hope it's a simple fix.

Regards

Dawson

[synsei]

This is a long shot but try pushing the drawer closed with your finger.

[daws0n]

Do you mean opening the tray and pushing it shut?

[synsei]

Aye :)

[StanleyB]

The tray open/close belt is gone. There is a mod that can be done on the belt to extend its life, but it is far too long winded for me to explain. Especially since you would need to open the unit and mess about inside it. I never assume anyone is capable of avoiding death through electrocution when bare life 240V wires are floating about in a piece of equipment. It is a common fault by the way, and one that some repairers use to milk the uninitiated with a claim that the whole mechanism needs replacing.

[daws0n]

No joy sadly, the mechanism runs smooth... The buzzing starts as soon as I press the eject button and does not stop until I kill the power completely.

[StanleyB]

No joy sadly, the mechanism runs smooth... The buzzing starts as soon as I press the eject button and does not stop until I kill the power completely.
Read my previous post: it's the tray belt. The buzzing is from the belt slipping over the motor pulley. The tray needs to be pulled in until it hits the "tray closed/open" detection switch. If it doesn't, it will keep the tray motor running at full speed.

[sq225917]

Replace the belt first, though it's more likely to be the small sensor that tells the drawer it is fully shut and to stop spinning the drawer open/close motor. Richer don't do 'at home' spares for them so dropping it In The local branch will result will be the best course and result in a new mech and a £200 bill.

The mech is their own design so aftermarket parts are pretty much none existant.

[daws0n]

Thanks for your input Stan, hadn't seen your post when I replied.

I think I understand what you're saying... New drive belt required to fix the motor spinning?

[StanleyB]

Thanks for your input Stan, hadn't seen your post when I replied.

I think I understand what you're saying... New drive belt required to fix the motor spinning?
You got it :). Or you can roughen up the belt with sand paper and put it back with the outside of the belt now facing inwards. It will make more sense when you fit and try it that way.
Just make sure the deck is not plugged into the mains when you work on it. The 240 Volts wires come into the chassis right behind the mechanism. That section is not enclosed, so lots of 240V exposed tracks and wires around that area.

[struth]

I will add that if the tray got out of sync by jamming it can jump a cog and misses the switch.... more likely to be the belt but you never know. I once used a o ring from a set I had kicking around my workshop and it was about the right size. just had to soften it up a bit and a little stretch....still working afaik.

AS STAN SAYS...=ALWAYS UNPLUG THE UNIT, AND LEAVE FOR A MINUTE OR SO BEFORE DIVING IN=

[daws0n]

I'll have a look tonight - 240v warning noted!

I was going to leave it powered up with the case off so I can see what's happening when it open and closes. I'll make sure I don't touch anything!

[sq225917]

The 240v comes in back right on the 840 and then straight into the traffo, everything is heat shrunken or shrouded on the back of the IEC so the only raw mains that exists is on the fuse cover and the legs of the two varistors. There's next to nowt showing on the wires to traffo either.

[daws0n]

I've had the lid off, and had a look... Everything looks OK! Nothing physical broken or out of place that I can tell:

http://daws.pzenix.com/cdp1.JPG
http://daws.pzenix.com/cdp2.JPG
http://daws.pzenix.com/cdp3.JPG
http://daws.pzenix.com/cdp4.JPG

However, it's now clear to hear that the noise is coming from the transport disc loading mechanism itself (somewhere on the bottom side I think). I have made a new video here:

http://daws.pzenix.com/cdp3.AVI

When the disc is loaded, it does not spin at all on the platter. I think the motor that spins it may be faulty but this is just guess work - any ideas guys?

Some good has come out of it though - for some reason since taking the lid off the buzzing has stopped happening when I turn it on and it has stopped trying to eject the tray over and over. Plus, it powers off OK without making the noise (so no need to kill at the mains) - it only makes that noise when I attempt to insert a disc now. So, at least that's an annoyance fixed and I can use it as a standalone DAC without issue.

[daws0n]

Original video links updated:

http://daws.pzenix.com/cdp1.AVI

http://daws.pzenix.com/cdp2.AVI

[StanleyB]

The belt you need to check is the one shown in the picture below.
http://www.homehifi.co.uk/aos/cdp4.JPG

[daws0n]

Couldn't see for looking there! Thanks Stan, I'll have another nose.

[daws0n]

I'm a total amateur with this sort if thing... Is it OK to sort to eject and load the tray with the lid off? Electrocution aside, is it safe to be near the laser beam while it's exposed?

[synsei]

It's fine, just don't stand over it and look directly at it ;)