Tivo has mains HUM, is there a fault?

[themib]

Hello everyone.

Ive had my tivo for some time, and when first installed had no issues.

There is a loud audio hum.

None of my other inputs to my sound system make this happen.

I have a pace NTL box as my source, the HUm increases in volume when I unplug the NTL.

I have tried the audio outs and its the same. (normally on scart output).

Could my Tivo have develloped a fault?

its quite loud. and has got worse, maybe it will get worse still. Any ideas.

[BrianHughes]

Try unplugging the leads, particularly the scarts and plugging them in firmly. In my experience that's nearly always been the cause of hum or ghosting on video.

Of course it's also possibly caused by electrolytic capacitors drying out - but we don't want to think about that.

[themib]

Try unplugging the leads, particularly the scarts and plugging them in firmly. In my experience that's nearly always been the cause of hum or ghosting on video.

Of course it's also possibly caused by electrolytic capacitors drying out - but we don't want to think about that.

I guess thats a major repair or replacement. There dont seem to be any loose cables

what does the capacitor problem exhibit?

[AMc]

Have you added or removed anything mains powered around the TV?
Mains hum can be a result of a thing called a "Ground loop" which happens when two interconnected bits of audio visual equipment have different earth voltages. Googling that term should shed some more light. Cable boxes are known for being culprits as they have a ground on the signal input that doesn't come from your mains supply I believe.

[blindlemon]

To expand on this slightly: Most AV equipment is double-shielded and hence doesn't require an earth in the mains lead. The potential of the alternating current in the devices is therefore "floating" WRT true earth.

However, sometimes one piece of equipment can end up "floating" at a different voltage WRT earth than another, so a voltage potential arises between them and the only way that this can be neutralised is for a small amount of mains-frequency current to flow through interconnects. When these are audio cables then you hear hum.

Try binding the metal casings of all your equipment together with an earth wire that's also attached to a good earth point - eg. mains earth - and if the problem is just a ground loop then the hum should go away.

[themib]

Thank you for the replies.

It only happens on the ntl/ tivo link. freeview box, dvd, vcr all fine.

If I unplug the NTL power it gets worse

then unplugging scarts didnt help.

Have you a link to how I may link up my equipment?
is it a case of wiring a wire to only the earth pin and connecting the wire to the other chassies?

It seems to have got worse over time, which points to a fault?

[6022tivo]

I also have this problem with my Pace NTL box connected.

Only difference, if I unplug the scart from my NTL box, the mains hum stops.

I think I will try the ground clamping of all the equipment.

[AMc]

The first test I would try is to connect everything up normally then unscrew the cable feed from the back of the NTL box. If the hum goes and you haven't changed anything else in your set up then it suggests a problem with the NTL green (?) box in the street which you may be able to get them to fix.

I had a problem with a ground loop between my amp and my subwoofer. That was easier to fix - I simply cut the 'ground' connection on the wire between them (the outer wire to outer connection) that isolated the two amplifiers and cured the problem without affecting the signal path. http://209.85.135.104/search?q=cache:bebE61H1N5gJ:www.avforums.com/forums/showthread.php%3Ft%3D227297%26highlight%3DAMc+ground+loop+av forums+amc&hl=en&gl=uk&ct=clnk&cd=1

Wiring all the chassis together sounds straight forward and should work but with about 8 items connected to the TV and speakers it is nigh on impossible to do.

Whatever you do DO NOT disconnect the earth pins from any earthed amplifiers/TVs etc. which I have heard advocated this is potentially fatal & could juice all your equipment even if it doesn't kill you.

Much better information from here...
http://www.users.bigpond.com/bcolliso/earth-loop.htm

[themib]

The first test I would try is to connect everything up normally then unscrew the cable feed from the back of the NTL box. If the hum goes and you haven't changed anything else in your set up then it suggests a problem with the NTL green (?) box in the street which you may be able to get them to fix.

I had a problem with a ground loop between my amp and my subwoofer. That was easier to fix - I simply cut the 'ground' connection on the wire between them (the outer wire to outer connection) that isolated the two amplifiers and cured the problem without affecting the signal path. http://209.85.135.104/search?q=cache:bebE61H1N5gJ:www.avforums.com/forums/showthread.php%3Ft%3D227297%26highlight%3DAMc+ground+loop+av forums+amc&hl=en&gl=uk&ct=clnk&cd=1

Wiring all the chassis together sounds straight forward and should work but with about 8 items connected to the TV and speakers it is nigh on impossible to do.

Whatever you do DO NOT disconnect the earth pins from any earthed amplifiers/TVs etc. which I have heard advocated this is potentially fatal & could juice all your equipment even if it doesn't kill you.

Much better information from here...
http://www.users.bigpond.com/bcolliso/earth-loop.htm

Thanks everyone, will try the ntl disconnect and report back

[themib]

Hi.

I totally disconnected NTL.
First cable input, still Hum,
Then scart, still Hum
and power, still Hum.

So that rules that out. It is definitely getting louder.

I will plug just the tivo, processor and 1 speaker in and see if that makes noise, if Tivo outputs hum on its own, no areal, or scarts connected and say in a menu, then surely it must be the box?

It was never like this before.

[AMc]

If it turns out to be Tivo then you may want to replace the power supply. I don't know enough about power supply design and ground loops to know if they are prone to cause this kind of problem before they fail but for a few quid it's probably the cheapest diagnostic.

They're cheap enough on eBay etc. or you can try http://www.tivoland.com/spare_parts.html or http://www.tivoheaven.co.uk/

[themib]

Thanks for the comments.
I have traced the problem to an 'analogue to digital' audio converter.

I have 2, they both introduce hum.

Im thinking that both are broken or their transformers as they are the same age.
Tivo sound direct to my processer doesnt have a hum and other audio inputs and outputs from my scaller dont have any issues.

[Pete77]

Im thinking that both are broken or their transformers as they are the same age.

I can't see why you think they are broken?

Surely they just operating on a frequency that clashes with the audio output stages of the Tivo in some way.

Have you done a Google search to see if anyone else has experienced hum from these units on other audio equipment?

[themib]

I can't see why you think they are broken?

Surely they just operating on a frequency that clashes with the audio output stages of the Tivo in some way.

Have you done a Google search to see if anyone else has experienced hum from these units on other audio equipment?


My hunch that they are broken, or maybe the transformers are stems from.

They didnt hum when I put them in 2 .5 years ago
If I turn the transformers off at night they hum worse when just turned on, before they, 'warm up'.

I didnt experience hum when they were new.
Ill try a new 9V transformer and find out if its that.

If they clash with the Tivo I would be surprised, but you may be right and no I havent found any other info yet.

[katman]

They didnt hum when I put them in 2 .5 years ago
If I turn the transformers off at night they hum worse when just turned on, before they, 'warm up'.

I didnt experience hum when they were new.
Ill try a new 9V transformer and find out if its that.


Sounds like the electrolytic capacitors in the power supplies have dried out and the units are trying to run of an unsmoothed supply.

New power supplies should sort it out.