505 SRDT tacho behaviour
  • Register
  • Help
Results 1 to 11 of 11
  1. #1
    Gus
    Gus is offline
    Fellow Frogger! Gus's Avatar
    Join Date
    Jun 2002
    Location
    Canberra, Australia
    Posts
    600

    Default 505 SRDT tacho behaviour

    Hi folks,

    I seem to have gotten the tach in my 505 SRDT (the alternator W-terminal driven type) moving (was stuck/broken), although I'm not sure if it's actually working. The behaviour I'm seeing is as follows (can anyone tell me if it's at all normal?)

    - When you turn the key to On, the needle swings around nearly 180 degrees from the Off spot.

    - When you start the engine, the needle jumps a little but doesn't really move.

    - If you rev the engine up from idle, the needle climbs clockwise at what looks like a roughly accurate rate (will confirm if/when the car is ever on the road.)

    Does that sound at all right? If so, can anyone tell me where the needle is meant to point to when the car is fully off (for calibration-ish purposes)?

    Thanks any/all who can help me out! Also, for the forty thousand dollar question:

    Advertisement


    - Does anyone know the ratio between the frequency of the square wave at the W-terminal and the engine's rpm?

  2. #2
    Demannu-facturing! Demannu's Avatar
    Join Date
    Dec 2002
    Location
    Menzies Creek
    Posts
    2,541

    Default

    - When you turn the key to On, the needle swings around nearly 180 degrees from the Off spot.
    Mine does the same.

    - When you start the engine, the needle jumps a little but doesn't really move.
    Again, mine does the same.

    - If you rev the engine up from idle, the needle climbs clockwise at what looks like a roughly accurate rate (will confirm if/when the car is ever on the road.)
    That's the idea of them, it sounds good!

    Does that sound at all right? If so, can anyone tell me where the needle is meant to point to when the car is fully off (for calibration-ish purposes)?
    Mine sits at about an imaginary 500rpm with the ignition off.

    - Does anyone know the ratio between the frequency of the square wave at the W-terminal and the engine's rpm?
    RPM x Crankshaft pulley circumference divided by alternator pulley circuference x number of poles in the alternator - most have 6.
    Scotty

    Melbourne - Dandenong Ranges

    1956 Peugeot 403 - 'Francois' - resto project

    1969 Peugeot 504 - 'Pascal' - daily driver project

    1970 Peugeot 404 Utility - 'Brutus' - resto project

    1978 Peugeot 604 - as yet unnamed - V6 on straight LPG

    1987 Peugeot 505 - as yet unnamed - project car

    1999 Peugeot 406 Coupé - 'Chloe' - 5 speed manual

    2011 Peugeot 3008 XTE HDi - 'Zoe' - hatchback on steroids

    2014 Peugeot RCZ - 'Remy'

    1999 Range Rover 4.6 HSE - 'Grover' - tow car

  3. #3
    Gus
    Gus is offline
    Fellow Frogger! Gus's Avatar
    Join Date
    Jun 2002
    Location
    Canberra, Australia
    Posts
    600

    Default

    Thanks Scott, but I'm just a little confused.

    Mine sits at about an imaginary 500rpm with the ignition off.
    Because mine swings around 180 degrees when you switch the ignition on, and doesn't return when you start the car, the Off position would need to be somewhere between 3-5000 rpm in order to get an accurate reading at idle. Do you mean 5000rpm, or does yours swing back when the engine starts?


    RPM x Crankshaft pulley circumference divided by alternator pulley circuference x number of poles in the alternator - most have 6.
    Thanks. That stands to reason. A couple of web sites made it sound like a black art (I guess if you want a fine-tuned response it is) but that sounds reasonable.

  4. #4
    Demannu-facturing! Demannu's Avatar
    Join Date
    Dec 2002
    Location
    Menzies Creek
    Posts
    2,541

    Default

    Because mine swings around 180 degrees when you switch the ignition on, and doesn't return when you start the car, the Off position would need to be somewhere between 3-5000 rpm in order to get an accurate reading at idle. Do you mean 5000rpm, or does yours swing back when the engine starts?
    Perhaps I should have been more accurate with my description there. When you turn the ignition to on, the tach swings around (more like "jumps" around" to about 180 degrees, and then bounces immediately back to the off position.

    The tacho in these cars, and in most cars, is basically just a galvanometer, that varies depending on the charge built up in a polarised capacitor through a low voltage zener diode network - basically the more energy in the pulses, the more the needle will deflect.

    It sounds to me like you have a stray DC voltage reaching the armature. If I were you, I would replace all the capacitors on the back of the tacho. When a capacitor dies, they can go open circuit or short circuit. A correctly operating capacitor in a series configuration is a high impedance to a DC current, but low to an AC current. If a capacitor has gone short, you will be getting stray voltages through to the armature.

    If you're handy with a soldering iron, it would not go astray just to replace all the components on the tacho PCB. It will only cost a few dollars for all the components (if you pay more than $10 you've been seriously shafted). Just be sure to note diode part numbers and capacitor polarisations.

    And if you can get access to an oscilloscope, check the output from the W terminal of the alternator. You should have 3 sine waves each 120 degrees out of phase when AC coupled. DC couple your probe and see how much ambient DC there is. I'm not sure what you should be expecting here, but if it is above 15 or 16 volts you may have issues inside the alternator.
    Scotty

    Melbourne - Dandenong Ranges

    1956 Peugeot 403 - 'Francois' - resto project

    1969 Peugeot 504 - 'Pascal' - daily driver project

    1970 Peugeot 404 Utility - 'Brutus' - resto project

    1978 Peugeot 604 - as yet unnamed - V6 on straight LPG

    1987 Peugeot 505 - as yet unnamed - project car

    1999 Peugeot 406 Coupé - 'Chloe' - 5 speed manual

    2011 Peugeot 3008 XTE HDi - 'Zoe' - hatchback on steroids

    2014 Peugeot RCZ - 'Remy'

    1999 Range Rover 4.6 HSE - 'Grover' - tow car

  5. #5
    Gus
    Gus is offline
    Fellow Frogger! Gus's Avatar
    Join Date
    Jun 2002
    Location
    Canberra, Australia
    Posts
    600

    Default

    Thanks Scott, that's good advice. I actually am reasonably handy with electronics (took electrical engineering courses as part of my Science degree) and was thinking that it may be something like that.

    I just wanted to check it wasn't "normal" behaviour, just in case. I'll pull all the capacitors off and test them.

    It also struck me that it could be some sort of floating ground connection in the module. Will check those too.

    Unfortunately, I have no access to a scope... although I have been looking for an excuse to buy one on ebay...

    Thanks again.

    (Ah, I love it when uni's back... lots of time to do random projects! .)
    Last edited by Gus; 21st February 2006 at 10:33 AM.

  6. #6
    Gus
    Gus is offline
    Fellow Frogger! Gus's Avatar
    Join Date
    Jun 2002
    Location
    Canberra, Australia
    Posts
    600

    Default

    (As a side note, the pcb doesn't actually use a diode network, but has two obscure-looking ICs on it.)

  7. #7
    Demannu-facturing! Demannu's Avatar
    Join Date
    Dec 2002
    Location
    Menzies Creek
    Posts
    2,541

    Default

    Quote Originally Posted by Gus
    (As a side note, the pcb doesn't actually use a diode network, but has two obscure-looking ICs on it.)
    Ahh crap. The french can be annoying.

    Still, if you are getting some sort of linear movement out of it at one point, it would suggest that the IC is working. There needs to be some chopping (voltage limiting) of the signal and accumulation of a charge for it to work at all, so your diode / capacitor network is working to a point. Replace everything else, and as you suggested, check for floating or faulty earths.

    PS - I still reckon you're getting a stray DC voltage to the armature. There will be more than one capacitor, one in paralel to the armature (charge accumulator), one in series with the feed line. The series one is a DC isolator from the diode network / IC, which operates on somewhere between 5 and 12 volts. If it has gone short, there will be VCC at the armature and across the armature. Remeber also that the voltage from the alternator W terminal has nothing to do with the system voltage in the car, it is an unregulated and unrectified signal from the alternator armature, so the voltage that drives the tacho could be well above VCC.
    Scotty

    Melbourne - Dandenong Ranges

    1956 Peugeot 403 - 'Francois' - resto project

    1969 Peugeot 504 - 'Pascal' - daily driver project

    1970 Peugeot 404 Utility - 'Brutus' - resto project

    1978 Peugeot 604 - as yet unnamed - V6 on straight LPG

    1987 Peugeot 505 - as yet unnamed - project car

    1999 Peugeot 406 Coupé - 'Chloe' - 5 speed manual

    2011 Peugeot 3008 XTE HDi - 'Zoe' - hatchback on steroids

    2014 Peugeot RCZ - 'Remy'

    1999 Range Rover 4.6 HSE - 'Grover' - tow car

  8. #8
    Gus
    Gus is offline
    Fellow Frogger! Gus's Avatar
    Join Date
    Jun 2002
    Location
    Canberra, Australia
    Posts
    600

    Default



    OK, if there's an AF goof of the week award, I think I just won it.

    I replaced all the electrolytic caps today ($1.20), and I'm out in the car giving it a test... no change. But I also notice that the off-idle movement is not as linear as I thought. . So then I take a closer look at the connectors at the back of the dash.

    There's no signal line hooked up for the tach! This car must have come without a tacho and someone's dropped a tacho-equipped dash into it!

    Further investigation showed that what I thought was the W line from the alternator ends in the engine bay. All I could get from it was less than 1v (AC or DC on my mm) so I'm guessing it's not even sending the right signal.

    Ah well, at least I've got somewhere to put a boost gauge now . Thanks for all the advice, Scott!

  9. #9
    Fellow Frogger! downunderyank's Avatar
    Join Date
    Aug 2005
    Location
    Longford Tas
    Posts
    220

    Default diesel tacho

    I really didn't think diesels ever came with tachs until 86 on. It was just your white car that had one and then Tassiediesel put one in as well. THere must be a way to hook it up as my GTD works well. SOme have said it is a crank trigger but I'll be damned if I can find it. Pretty funny story though!
    Before you judge someone, walk a mile in their shoes. Then when you judge them, you're a mile away and you've got thier shoes!

  10. #10
    Demannu-facturing! Demannu's Avatar
    Join Date
    Dec 2002
    Location
    Menzies Creek
    Posts
    2,541

    Default

    From what I've seen, about a quarter of series 1 SRDTs had tachos.

    Their signal is driven from the "W" terminal of the alternator.

    Gus, there is still hope. But you will need to ensure that you have a diesel tacho, as the standard petrol one triggered by the ignition system will not work with the W signal.

    If you have a diesel tacho, you can add the wire neccesary. Either find a volounteer to pull theirs apart to check which connections are neccesary, or find a wiring diagram for a tacho-equipped diesel, then make the changes!

    The easiest way to tell if you have a diesel tacho, is to check where the redline is set. 2 litre 505s have it at 5600, I think my SRDT is 5000. The ZDJ motors I can't remember off the top of my head, but I think it might be the same as the XNs.
    Scotty

    Melbourne - Dandenong Ranges

    1956 Peugeot 403 - 'Francois' - resto project

    1969 Peugeot 504 - 'Pascal' - daily driver project

    1970 Peugeot 404 Utility - 'Brutus' - resto project

    1978 Peugeot 604 - as yet unnamed - V6 on straight LPG

    1987 Peugeot 505 - as yet unnamed - project car

    1999 Peugeot 406 Coupé - 'Chloe' - 5 speed manual

    2011 Peugeot 3008 XTE HDi - 'Zoe' - hatchback on steroids

    2014 Peugeot RCZ - 'Remy'

    1999 Range Rover 4.6 HSE - 'Grover' - tow car

  11. #11
    Gus
    Gus is offline
    Fellow Frogger! Gus's Avatar
    Join Date
    Jun 2002
    Location
    Canberra, Australia
    Posts
    600

    Default

    Scott,

    Thanks for the encouraging words. The extra wiring is dead simple - one wire from the W terminal to the (currently missing) third connection to the tacho.

    I think it's definitely a diesel tach (4500rpm redline), but I'm still not sure about the W signal. From what I can gather on the net, not all distributors even have a W terminal available... and seeing as I'm not getting any decent voltage reading from the small line coming from mine, I think mine might not have one... I have some time this morning, so I might rig up a wire into the cabin and check that the wire I have doesn't work, just to be sure.

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •