Constant faint tone coming from on board computer gong

[alfie007]

My OBC gong constantly has a faint tone coming from it even when the engine and everything else is swtiched off. The car is a 325I Sport and fuse 21 serves the computer amongst other things such as the courtesey lights, rev counter and stereo. When I remove the fuse overnight and pop it back in, all works normally but then the tone returns a few hours later. Any suggestions or tips I can forward to a competant auto electrician? Can anyone reccomend a good spark in the Edinburgh area that may be able to help.

[Brianmoooore]

The OBC sounder unit produces it gong sound by an amplifier and speaker connected to a constantly running astable oscillator which produces a continuous musical note. Between the two is an electronically controlled volume control, which, when the gong is activated, turns up the volume and then turns it down again.
The problem with yours is that the volume control isn't quite being turned down to zero, so the tone is getting through all the time.
I came across one like this once, and cured it. IIRC, I couldn't find out what exactly was wrong with it and ended up modifying it slightly. Unfortunately, although I still have the circuit diagram for the gong, I didn't write down what I did, and certainly can't remember.
I still have that gong in one of my cars, and it's still working properly after three years.

[eko]

Fooking hell Brian,you never cease to amaze me with your knowledge,you always havew an answer

Are you a BMW trained mechanic or is it just what youve learnt `along the way`?

[Brianmoooore]

is it just what youve learnt `along the way`?

Just what I've learnt along the way.
As I've said in the post, I came across this problem myself, and was determined to repair the thing, so I had to strip it right down, trace out the circuit, identify all the bits and work out how it worked, before I could hope to find out what was wrong with it.

[eko]

Clever b4stard

but we all love you

sorry for the off topic alfie007

[alfie007]

Cheers for your reply Brian, BUT...this sounds rather complicated and out of my technical expertise re. repair. The problem seems to have occured a couple of weeks after I had a new alarm/immobilizer fitted. The installers are going to have a look but given your reply, this problem is probably just a coincidence. You suggest my car's gong volume control seems to be the cause, how easy would this be to replace/repair and where is it situated? Is it part of the computer in the dash or the gong unit near the steering collumn or elsewhere. Ideally a competant spark would be able to have a look but a number I've used in the past are clueless hack-merchants (not wishing to generalise!) and have hindered rather than helped. I've posted a wanted topic for a new computer and gong and have had a reply for both at £50. Would either being replaced solve the problem? Aside from this noise, the computer works perfectly well.

[smithy318i]

Brian. Now that your not using a laptop, Following on from my PM (months ago) can you send me the diagram for the gong please!

[Gortour]

The OBC sounder unit produces it gong sound by an amplifier and speaker connected to a constantly running astable oscillator which produces a continuous musical note. Between the two is an electronically controlled volume control, which, when the gong is activated, turns up the volume and then turns it down again.

Foo Kin Ell... That's a bit of a mouthful, regardless of understanding it...
Again Brian's knowledge is exemplary... Brilliant.
Wierd way to make a 'boing', but it works I suppose...

[Brianmoooore]

Is it part of the computer in the dash or the gong unit near the steering column or elsewhere. .

It's all in the gong unit.
The gong has three wire going to it which are earth (brown), 12V+ (I think red/green or red/white) and trigger (I think brown/yellow).
If you touch the trigger wire to earth, the gong will sound.

[Brianmoooore]

Brian. Now that your not using a laptop, Following on from my PM (months ago) can you send me the diagram for the gong please!

You're welcome to a copy, Smithy, if I can work out how a) to get it from a piece of paper into an electronic form, and b) how to send it.
PM me an email address as a start.

[Speedtouch]

http://www.e30zone.net/modules.php?name ... highlight=

[Brianmoooore]

http://www.e30zone.net/modules.php?name ... highlight=

Can't remember posting that at all!!

[Royalratch]

Hi guys.

Brian, is the gong necessary for the OBC to work? I guess it's there to notify you of something but what?

If you were doing a retrofit, would leaving the gong out affect the function of the system in any way?

[Brianmoooore]

Hi guys.

Brian, is the gong necessary for the OBC to work? I guess it's there to notify you of something but what?

If you were doing a retrofit, would leaving the gong out affect the function of the system in any way?

OBC works OK without the gong, but it draws your attention to it when the ice warning comes on or you go over the speed limiter.

[Speedtouch]

I've never even heard mine (it is connected) I'll do a swap Alfie007, if you like

[Brianmoooore]

I've never even heard mine (it is connected) I'll do a swap Alfie007, if you like

Set your speed limiter to a suitably low speed and drive faster than it's set.
As you exceed the set limit the gong should sound once, and the LED by the speed button should flash continuously.

[Royalratch]

I had an OBC in an older 325i Touring but could not even set the clock let alone use all those functions!

And I'm pretty technical with gadgets.

Is there a manual knocking around?

[Speedtouch]

Here: http://www.dufferdesigns.com/E30OwnersManual.pdf

[smithy318i]

I had an OBC in an older 325i Touring but could not even set the clock let alone use all those functions!

And I'm pretty technical with gadgets.

Is there a manual knocking around?

http://www.isohunt.com/download/16146448/e30

[Speedtouch]

Discovered why my gong has never sounded today: it's speaker is up the creak - gone open circuit Alas, it's an unusual type, 80 Ohm 0.3 Watt oval shape. Anyone know where i can get another?

Cheers!

[Brianmoooore]

CPC lists a 30mm dia. 100 ohm one, and a 60mm dia. 64 ohm one. Or raid an E36/E34.

[Speedtouch]

For my first time ever in around 4 collective years of E30 ownership (across 3 models), I got to hear the glorious resounding gong of the obc tonight. In fact, I deliberately slowed down and speeded up a number of times to hear it again and again

Thanks to ag-1982 for supplying a working unit to replace my broken one