Date: Sat, 5 Jul 2014 01:48:46 -0400
Reply-To: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject: Re: AFM test readings
In-Reply-To: <53B5ED9F.8040606@gmail.com>
Content-Type: text/plain; charset="utf-8"
Looking for value in a "swing" meter these days is almost like looking for a good deal on a television with a CRT screen or a VCR. Seriously, if willing to invest in anything look for a digital meter that includes an analogue bar graph display. These displays are way faster than the number screen and will blow away any mechanical meter in response time. Also, many of these meters will have hold functions. To test parts of the fuel injection having duty cycle or frequency functions are a must. These meters will also usually take more abuse than swing meters.
Dennis
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Rocket J Squirrel
Sent: Thursday, July 3, 2014 7:56 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: AFM test readings
David's suggestion to use an analog voltmeter is a good one. Analog meters catch glitches and dropouts that digital meters don't.
The question is -- who has a good value in an analog multimeter these days? Simpsons were my go-tos in Ye Days of Olde when Knights Were Bold and I had a budget.
--
Jack "Rocket j Squirrel" Elliott
1984 Westfalia, auto trans,
Bend, Ore.
On 07/03/2014 04:12 PM, Harold Teer wrote:
> David,
>
> Thanks for a great and detailed explanation on the AFM that even I
> understand. Between the information from you, Karl, and Neil, this
> thread will be a wonderful resource in the archives for understanding
> the AFM better.
>
> Have a great weekend and 4th of July,
>
> Harold
>
> Harold Teer
> 1991 Westy -- VANGAUX
> Harrisonburg, VA
>
>
>
> On Thu, Jul 3, 2014 at 5:08 PM, David Beierl <dbeierl@attglobal.net> wrote:
>
>> At 09:10 AM 7/3/2014, Harold Teer wrote:
>>
>>> Thanks, this makes sense in theory. Â Can you walk me through how to
>>> do this without the AFM connected if I don't have any fancy
>>> equipment. Â Do have analog and digital meters so have that part covered.
>>>
>>
>> To do it with the AFM in the van, follow the procedure in
>> tencentlife's video. Pull the boot off the connector, stick your
>> meter probes in as he shows, turn on the ignition and follow his
>> procedure of very slowly pushing the AFM vane open with a stick of
>> some sort. You have to be slow enough that the meter has time to
>> respond to any dropouts. Notice he's using a fairly small meter with
>> a fairly quick-responding needle. If you have a larger one that
>> responds very slowly (like a couple of Radio Shack meters I
>> have) you have to move the vane slow enough that you can see the
>> needle dip. Any dip at all means a problem at that point on the
>> track, you don't have to wait for it to fall to zero; you should see
>> the voltage only rising as you push the vane open.
>>
>> To do it using dry cells or a power supply (and having been reminded
>> by Neil's photo of the resistor plate itself, I expect a nine-volt
>> square battery would be fine and maybe easier to hook up to), hook up
>> the battery to the same pins the ECU would use. I don't have access
>> to a Bentley right now but according to the video the AFM pins for the waterboxers are:
>>
>> 1 - Temp I hot
>> 2 - AFM wiper
>> 3 - AFM + supply
>> 4 - System ground for both AFM and Temp I
>>
>> So you'd hook B+ to pin 3 and B- to pin 4. You'd hook meter + to pin
>> 2 and meter - to pin 4.
>>
>> Don't use your digital meter, it will only cause you grief. It
>> probably only takes 2-3 readings per second, and the reading is
>> averaged over the sampling time which is less than half of the half-
>> or third-second cycle time. If your meter has a quick-responding bar
>> graph display you might manage; but the analog meter responds in real
>> time and is always reading the line. Even if the needle response is
>> slow it will be easier to deal with than the digital (may or may not be easier than the bar graph display.
>>
>> If for some reason you do use the digital, set it on a fixed range,
>> as you don't want it switching ranges while you're testing.
>>
>> Set your meter range as low as practical that's at least half the
>> input voltage. As tcl says that will cover the part of the AFM track
>> that gets the wear.
>>
>> FYI, if you look at Neil's photo of an uninistalled resistor plate:
>> https://lh6.googleusercontent.com/-c5axVMck2Ks/T-tDy8qL_MI/
>> AAAAAAAAF2o/Cly2OSeHmUk/s912/AFM%2520Board%2520Wear.jpg
>>
>> At the bottom there's the Bourns name and Bosch symbol, indicating a
>> proprietary part made for Bosch. 8712 means it was made in week 12
>> of 1987. The two crosses and two triangles I imagine are
>> registration test marks for the several layers of stuff that get
>> printed onto the ceramic substrate. The spot on the left-hand triangle may be an inspector's mark.
>> The long number is Bourns' part number for the plate, the 1
>> probably means revision 1 of the device, and the reversed C looks
>> like a test resistor to validate the resistor printing process for
>> quality control
>>
>> Above that is the wiper track. The right side is the ground side and
>> the left side is hot, corresponding to the rotation of the vane in the AFM.
>>
>> Now look at the very top. The two bright dots are where the spring
>> contacts have burnished the silver paint that forms the conductors.
>> Theleft one is + and the right one -. Following them, you'll see
>> that each connects to a green patch with lines on it. Those are
>> resistors, and the lines are where the trimming laser burned away
>> parts of the resistor to increase its resistance to the correct value.
>>
>> From the other end of the resistor conductors go to the two ends of
>> the wiper track. If they were the only connections you'd be able to
>> do this test with an analog ohmmeter instead of a voltmeter. But as
>> you can see there is also a resistor that stretches the entire length
>> of the track, with nine connections into the track and laser trims
>> between each pair of connections. That's what's driving your
>> ohmmeter nuts. It's a voltage divider that's feeding an offset
>> voltage into the track at those nine points to adjust the wiper
>> response. When Bourns builds the plate the laser trimmer has point
>> contacts that leave the tiny bright mark on the little side tabs
>> coming away from the various resistors, and it trims the resistors in
>> a particular sequence until all the values are correct. It looks as
>> though it does a roughing pass and then a finishing pass to take care
>> of interaction between the voltage divider and the two main input
>> resistors. Then they ship it to Bosch who glue it onto the metal mounting plate.
>>
>> While I'm on the subject, in tcl's video the long copper arm is
>> carries the contact from the AFM connector to the wiper. It has a
>> carbon button in the round end ant there's a flat spring with a bump
>> on it that comes up from the vane/wiper assembly and presses on it.
>> However apparently there were difficulties with this, because by at
>> least late '83 Bosch had added a braided copper flex cable to bypass this button and make a solid connection.
>>
>> Yours,
>> David
>>
