HU850 in '05 V70/D5 acting up...

[nickds1]

Hi,

The HU850 radio in our '05 V70 has recently started acting oddly - the display seems fine, but the audio keeps cutting out or not coming on at all and occasionally the unit just power off.

Cabling seems fine - do these units have a separate power amp or is there something else I should be looking for.

Thanks

EDIT: Bit more on this - took the console out - all cabling seems OK, put it back in and now everything "seems" to work except FM, which is dead as a post - the CD plays fine, AM is OK, but on FM? Nada...

[oragex]

The HU-850 and the HU-813 have a separate amp under the front pass seat which provides the sound to the unit. Because of it's location, this amp often times gets corroded leaving the radio unit with no sound. Can be bought used off Ebay. or the unit can be replaced with a HU-600 that fits (same front panel shape) which doesn't require an amp.

If the fm is acting and the cd works, maybe the radio unit is faulty. May try replacing it with a used one

Warning: do not disconnect any cable while having the key in the ignition. Even better, disconnect the car battery before removing any cable.

[Simon Jones]

The amp is under the drivers seat in the UK. However, as the centre speaker is driven directly by the HU so if that is also cutting out, then the problem is the HU and not the amp.

[oragex]

Thanks Simon for clarifying.
While there, worth mentioning the HU-813 seems to have better sound than the HU-850. Just be aware there are two front plate shapes, which are not interchangeable. Also, try finding a unit from a car year close to yours, otherwise steering volume control buttons may not work.

[nickds1]

More on this, now I have time to chase it...

I'm an electronic engineer by training, so I'm happy with the internals of stuff like this...

What I'm seeing is that the RF & interface of the FM sections is fine - the unit searches and does RDS correctly etc, and on AM works fine (if you like French stations...) so the amplifier is also good.

So, my feeling is that it's an analogue switch in the final part of the radio, prior to the power amp, that's failed... i.e. a component failure. If it is an analogue switch, I should be able to replace that/

Does anyone have a service manual for these units? It would make tracing this far easier...

Ta!

[Symes]

Hi, mines been playing up in the same way for about a Year, CD and CDChanger are fine but FM drops in and out at best and doesn't provide anything at worst... Haven't managed to determine any comminality in terms of temperature or vibration, but suspect it's a failed solder joint on the FM output. The disassembly to get to the PCB is time consuming and TBH I haven't had the inclination to remove the hu to start to investigate yet. ;-)

[nickds1]

I suspect that it's a failed analogue switch. These are pretty common parts and readily identifiable - I'll trace the audio from the FM output (using a scope and a fixed tone FM signal) till I find the failed component. That's the plan, anyway... 🤔

[seanbont]

Our hi-850 (05 s60) has just started having a problem with fm volume. Am and cd volume works great but fm doesn’t.
Tunes fine and you can hear the station but barely. Turning the volume up has no effect when on fm (1, 2 or 3) All the other controls work in fade balance etc and all speakers work.
With cd or am the sound is great.
Would really appreciate any suggestions of what it could be please.

[nickds1]

This failure mode seems pretty common - I see it on a lot of forums - am still looking for the manual though!

Haven't got round to this yet, but will in the next few weeks.

[gjm120761]

I'm another. 2005 XC70.
HU-850 with factory phone/satnav
had the car since 3 years old.
about a year ago, noticed no lights on the buttons
then FM stopped working. occasionall it will come on for a while then off again. all other audio works fine.
so if anyone traced a solution, or found someone to repair, would be interested to hear of solution/approx cost please.
regards Graham