Date: Fri, 4 Jul 2014 08:02:08 -0400
Reply-To: Larry Alofs <lalofs@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Larry Alofs <lalofs@GMAIL.COM>
Subject: Re: AFM test readings
In-Reply-To: <53B65CE1.3090606@turbovans.com>
Content-Type: text/plain; charset=UTF-8
Scott,
Do you have a link? When I search at the HF site, all the meters are
digital except one that mounts in the dash.
Larry A.
On Fri, Jul 4, 2014 at 3:50 AM, SDF ( aka ;jim lahey' - Scott ) <
scottdaniel@turbovans.com> wrote:
> if your goal is an inexpensive basic analogue volt meter..
> they can be as low at $ 4.95 or even $ 3.95 at Harbor Freight ..and in
> Oregon ..no sales tax either.
> or...
> like 15 bucks will go a long way toward getting one that's decent enough.
>
>
> On 7/3/2014 1:56 PM, Rocket J Squirrel wrote:
>
>> 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
>>>>
>>>>
>>
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