Zener diode question for dop control circuit

[camper]

On the wiki there is comprehensive circuit diagrams and test procedures for the buzzer of doom for low&high oil pressure for the WBX and diesel engines.There is a zener diode for the water boxer & diesel engine version ofthe t25 located on the rear of the instrument that is discribed in the wiki circuit as the control for the high& oil pressure circuit or DOP .My question is this does this same zener diode control the fuel & tempreture gauge ? As on the Aircooled engine version the fuel gauge is discribed as controlled by the zener diode and if the gauge becomes faulty there is a test procedure ie measuring its voltage control over the fuel gauge.I am having problems with my diesel engined van as unable to get the high oil pressure buzzer circuit to work but the fuel & tempreture gauge is okay .

[dave friday]

as your fuel and temperature gauges are ok, i would be looking for the rev-counter signal at the dop board pin 1 on j 114 [does the rev-counter work?].

[camper]

I tested the rev counter pin on the DOP and its 12 volts ignition on or off ie constant .The rev counter pin reads 12 volts off the the spade terminal from the alternater regardless of ignition on or off is this correct on the alternater for the diesel engine ? The wiki discribes the WBX petrol engine rev counter pin rev supply taken from the ignition coil terminal and live when the ignition key is turned on.For the DOP circuit to work the high pressure warning how does it measure 2000 rpm from the alternater and a way to test the signal?.Thanks for replies.

[Grun]

camper,

here is a link to the brickyard forum, and if you scroll down there is a post from non other than 'dave friday' with some info on wiring connections to the alternator.

I think the 'W' terminal only gives an (alternating) signal when engine running. I also have a photo of the pin connections to the PCB and...... pin 9-Tachometer, terminal 1/W....... is what is shown.

I have done a little reading on the function of a zener diode, and have a feeling that as installed in the instrument PCB it is there to guard against voltage surge rather than voltage regulation,(the voltage stabilizer takes care of that).



Hope this may help.
Mike

[camper]

Thanks Mike it does help.The spade terminal to the DOP on the alternater measures + 12 volts no revs .The question is is this correct or should it be only a generated voltage frequency supply to the DOP .It could be that i have a faulty alternater.

[Grun]

Thanks Mike it does help.The spade terminal to the DOP on the alternater measures + 12 volts no revs .The question is is this correct or should it be only a generated voltage frequency supply to the DOP .It could be that i have a faulty alternater.

camper,
I am no expert in electrics/electronics, but it appears that some alternators do not have the 'W' terminal fitted as standard.
I think that the signal from the 'W' terminal will be alternating and will rise in frequency as the alternator RPM rises.
The signal from terminal 1 of the coil on a petrol engine will be a pulsed DC as the Hall sender switches the coil primary on and off.
I have found a link showing a modification to an alternator to provide a signal HERE
The signal is tapped off before the diode(rectifier) pack.
Have a look, there is a photo if you scroll down.
Mike

[camper]

Thanks again mIke two heads are better than one for sure.Well it does look like this is the problem .The link for the W mod is appreciated.

[Grun]

Camper,
If you go to.........http://www.vanagon.com/" onclick="window.open(this.href);return false; and under 'Problems'... Oil pressure problems......'Oil Pressure Problems' by Karl Bloss,
is an article on fitting a pressure gauge, scroll down as there are some useful hints even if it refers to the waterboxer engine.
Mike

[dave friday]

Grun is right about the zener diode fitted to kill voltage peaks from the ign coil ect, i just meausered the ouput from the "W" terminal [with a cheep digital meter ] meter on dc, zero volts [engine off] 7.12 volts dc engine at 950rpm and 16.1 volts ac, so you seem to have a problem with the "W" output. if you want to pm me with your phone number i could talk you through it?.
good luck.

[camper]

The van is a 1.6td recently fitted with a 1Y engine.Looking at the alternater it is not specific for a diesel version with the W terminal.There is a + marked next to the spade connection which the dop circuit is taking its signal from this is incorrect .So its a choice now of trying to mod the existing alternater as suggested in the link provided by grun or a replacement alternater with a W connection.Thanks for the offer to talk it through Dave friday but untill i sort out the alternater i carnt do anythink yet.

[Grun]

camper,
Glad you have tracked down the problem, could this be the solution?
https://club8090.co.uk/forum/viewtopic.php?f=17&t=47536" onclick="window.open(this.href);return false;
Mike