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kirtfitzpatrick Samba Member
Joined: July 12, 2014 Posts: 55 Location: San Francisco, CA
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Posted: Wed Dec 16, 2020 2:28 pm Post subject: Coolant Temp Gauge Rebuild w/parts list & photos |
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My coolant light has been blinking at me for years and every diagnostic test I tried was inconclusive as to what was causing it. I even unsoldered the capacitor and it tested out okay. Since I was unable to buy a used gauge I was left needing to fix this one. So I unsoldered all the resistors, diodes, chips and cap to test them individually.
Since I had to remove all the components to test them I wasn’t about to solder old and possibly bad components back on so I figured out the specs of each part and ordered new ones. It was a grand total of about $2 from Digikey and $10 from McMaster.
All in all it wasn’t that hard to swap everything out. I never did figure out which part was the bad one but it must have been one of the diodes or the op amp. The resistors and cap all tested perfect but I’m not very familiar with testing diodes and I didn’t test the op-amp.
My gauge is from an ’88 and below is the parts list and some photos. I figured this would be helpful to anyone out there contemplating rebuilding their gauge. My gauge finally works again! And it was a simple matter to calibrate it to dead center over the LED once I was finished.
Hex nut
Button head hex drive bolt3-48 thread
1/4” length
black oxide finish
Capacitor
OpAmp
Diode 1blue, above LED
BZX55C5v1
Resistor 14 bands (purple green yellow gold)
750 kΩ
Resistor 25 bands (brown black purple red brown)
10.7 kΩ
Resistor 35 bands (brown brown green red brown)
11.5 kΩ
Diode 2
Resistor 44 bands, next to cap (brown green yellow gold)
150 kΩ
The original gauge: The two big solder joints, bottom-left and top-right, are the posts that mount the PCB to the metal cup.
The original components.
I upgraded my soldering setup a little for this. I have plenty of soldering experience but not much with PCBs. This was the most ambitious electronics repair I've yet attempted. Not pictured is the solder wick I used to unsolder everything and clean off the board.
The toothed arms are for calibrating the needle position. Set them to the middle of their travel initially. Then adjust the bottom one to set the needle in the correct position when the van is off. And adjust the upper arm when you know the van is at optimal temperature to set the needle to the middle of the LED. I used a temperature gun for this.
Everything except the LED here is new. I knew with absolute certainty that the LED worked already.
I added some heat shrink over the thin wire because the enamel had worn off in places. From the factory this wire is soldered into a tiny horizontal hole in the post. Pull very gently on the wire and give the post a lot of heat until the solder inside liquifies and lets go.
The marks on the face are from a mechanic that tried to work on it years ago. It looked even worse than this before I hammered it flat again. Drill out the faceplate rivets if you want to work on your gauge.
Hope this helps! _________________ @tintopcamper
YouTube
Last edited by kirtfitzpatrick on Sun Feb 07, 2021 2:20 pm; edited 4 times in total |
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[email protected] Samba Member
Joined: April 29, 2015 Posts: 704 Location: Berkeley Ca
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Posted: Wed Dec 16, 2020 2:56 pm Post subject: Re: Coolant Temp Gauge Rebuild w/parts list and photos |
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Killer thanks |
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NorthOf50 Samba Member
Joined: October 13, 2020 Posts: 102 Location: Campbell River, BC
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Posted: Sun Jan 17, 2021 10:34 pm Post subject: Re: Coolant Temp Gauge Rebuild w/parts list & photos |
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thanks. I think I need to rebuild mine as I am fairly certain my LED is kaput. the gauge works fine but the LED never blinks. I've got the gauge on my kitchen table, about to drill out the rivets to open 'er up! _________________ '84 1.9WBX Camper (Penny)
'88 2.1WBX Camper (Martin)
Last edited by NorthOf50 on Mon Jan 18, 2021 1:29 pm; edited 1 time in total |
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djkeev Samba Moderator
Joined: September 30, 2007 Posts: 32574 Location: Reading Pennsylvania
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NorthOf50 Samba Member
Joined: October 13, 2020 Posts: 102 Location: Campbell River, BC
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Posted: Mon Jan 18, 2021 10:37 pm Post subject: Re: Coolant Temp Gauge Rebuild w/parts list & photos |
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I believe the PN for the original gauge is either: 251919511A or 251919511C depending on if the van is 86+ or 86-
*removed image until I can get the parts list corrected _________________ '84 1.9WBX Camper (Penny)
'88 2.1WBX Camper (Martin)
Last edited by NorthOf50 on Tue Jan 19, 2021 10:48 pm; edited 2 times in total |
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kirtfitzpatrick Samba Member
Joined: July 12, 2014 Posts: 55 Location: San Francisco, CA
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Posted: Tue Jan 19, 2021 10:03 am Post subject: Re: Coolant Temp Gauge Rebuild w/parts list & photos |
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NorthOf50 wrote: |
I believe I have the correct parts list from Digikey here, please correct me if I'm wrong and I'll update it as I'm new to sourcing individual components.
... |
A couple of those resistors look incorrect to me. Sorry I can't drive deeper at the moment as I'm driving cross country. _________________ @tintopcamper
YouTube
Last edited by kirtfitzpatrick on Wed Jan 27, 2021 4:56 pm; edited 1 time in total |
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crazyvwvanman Samba Member
Joined: January 28, 2008 Posts: 9920 Location: Orbiting San Diego
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Posted: Tue Jan 19, 2021 10:40 am Post subject: Re: Coolant Temp Gauge Rebuild w/parts list & photos |
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That capacitor doesn't look like the right specs.
Your list shows 1000 mfd 10v
The list given earlier shows 10 mfd 16v
Haven't compared the other parts listed.
Mark
NorthOf50 wrote: |
I believe I have the correct parts list from Digikey here, please correct me if I'm wrong and I'll update it as I'm new to sourcing individual components.
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NorthOf50 Samba Member
Joined: October 13, 2020 Posts: 102 Location: Campbell River, BC
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Posted: Tue Jan 19, 2021 9:55 pm Post subject: Re: Coolant Temp Gauge Rebuild w/parts list & photos |
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yeah turns out I wasn't paying close enough attention, too late at night!
Digikey seems to have everything but the 11.5K ohm resistor. trying to build a parts list @ Mouser instead...Someone want to error check this?
https://www.mouser.ca/ProjectManager/ProjectDetail.aspx?AccessID=a865bde165
Mouser # Mfr. # Manufacturer Customer # Description
1 926-LM741CN/NOPB LM741CN/NOPB Texas Instruments Operational Amplifiers - Op Amps Op-Amp
2 74-199D106X9016C6VE3 199D106X9016C6V1E3 Vishay Tantalum Capacitors - Solid Leaded 10uF 16volts 10% C case .20 LS Radial
3 78-BZX55C5V1 BZX55C5V1-TR Vishay Zener Diodes 5.1 Volt 0.5W 5%
4 603-CFR-50JB-52-750K CFR-50JB-52-750K Yageo Carbon Film Resistors - Through Hole 750K ohm 5% 1/2W Carbon Film
5 71-CMF5510K700FHEB CMF5510K700FHEB Vishay Metal Film Resistors - Through Hole 1/2watt 10.7Kohm 1% 50ppm
6 660-MF1/2CC1152F MF1/2CC1152F KOA Speer Metal Film Resistors - Through Hole 11.5Kohms 1% 50PPM
7 512-1N4148 1N4148 ON Semiconductor Diodes - General Purpose, Power, Switching 100V Io/200mA BULK
8 588-OL1545E-R52 OL1545E-R52 Ohmite Carbon Film Resistors - Through Hole 150K Ohm 1/2W 5% 350 Volt _________________ '84 1.9WBX Camper (Penny)
'88 2.1WBX Camper (Martin)
Last edited by NorthOf50 on Wed Jan 27, 2021 4:09 pm; edited 1 time in total |
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DanHoug Samba Member
Joined: December 05, 2016 Posts: 4770 Location: Bemidji, MN
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Posted: Wed Jan 20, 2021 10:47 am Post subject: Re: Coolant Temp Gauge Rebuild w/parts list & photos |
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if you don't have the resistors, i'll guarantee that the existing ones are good and you can re-use them, or at least the one you don't have. just measure it for ohms to see if it matches. most likely, the cap was bad and you've substituted a tantalum instead of the aluminum electrolytic. that's fine.
edit: i see you tested the cap.. depending upon the test unit, may or may not reveal a problem but congrats on fixing it! _________________ -dan
60% of what you find on the internet is wrong, including this post.
'87 Westy & '89 Westy both 2.1 4spd
Past projects can be found at--
www.thefixitworkshop.com |
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NorthOf50 Samba Member
Joined: October 13, 2020 Posts: 102 Location: Campbell River, BC
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Posted: Wed Jan 27, 2021 2:49 pm Post subject: Re: Coolant Temp Gauge Rebuild w/parts list & photos |
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the plot thickens...
I completed my rebuild last night and tested my gauge today. all new components, LED included. the gauge works (still) however my LED still does not blink!! argh!!! I have verified that I installed it in the same polarity as the original LED. I have tested the new LED in place w/ diode test and it works in place. Why is it not getting V to light up? any ideas? my board was in really nice shape and the needle etc functions.
I'm back to square 1 with a non-working LED!!! _________________ '84 1.9WBX Camper (Penny)
'88 2.1WBX Camper (Martin) |
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crazyvwvanman Samba Member
Joined: January 28, 2008 Posts: 9920 Location: Orbiting San Diego
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Posted: Wed Jan 27, 2021 2:56 pm Post subject: Re: Coolant Temp Gauge Rebuild w/parts list & photos |
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Do you have a photo of the board after you swapped all the parts?
I think 4 or 5 of the parts have polarity and must be installed connected the right way.
Mark |
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fxr Samba Member
Joined: December 07, 2014 Posts: 2319 Location: Bay area CA
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Posted: Wed Jan 27, 2021 3:34 pm Post subject: Re: Coolant Temp Gauge Rebuild w/parts list & photos |
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Isn't the original R3 1k25 , not 11k5 ? Did you measure them all? _________________ Jim Crowther
1984 1.9l EJ22 Westy Wolfsburg Edition
Vespa GTS 300 |
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NorthOf50 Samba Member
Joined: October 13, 2020 Posts: 102 Location: Campbell River, BC
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Posted: Wed Jan 27, 2021 4:01 pm Post subject: Re: Coolant Temp Gauge Rebuild w/parts list & photos |
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Before and after photos of the boards. I was pretty careful to match polarity, but I am new to this so it is possible I missed something.
and after
I measured all the resistors that were removed to confirm that they were in fact what was stated by the OP. He's bang on. The only difference is that I ordered 1% tolerance resistors for my replacements, where previously some are 5%. I tested everything that came out, and it all seemed to test good. I don't know how to test the OpAmp but regardless the LED didn't work before and doesn't now. I know the ground is good as I also replaced my high beam indicator LED which shares the same ground and it now works properly.... _________________ '84 1.9WBX Camper (Penny)
'88 2.1WBX Camper (Martin) |
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DanHoug Samba Member
Joined: December 05, 2016 Posts: 4770 Location: Bemidji, MN
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Posted: Wed Jan 27, 2021 4:12 pm Post subject: Re: Coolant Temp Gauge Rebuild w/parts list & photos |
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unable to determine from your photos the polarity of the tantalum cap. the negative lead should be closest to the IC chip. _________________ -dan
60% of what you find on the internet is wrong, including this post.
'87 Westy & '89 Westy both 2.1 4spd
Past projects can be found at--
www.thefixitworkshop.com |
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kirtfitzpatrick Samba Member
Joined: July 12, 2014 Posts: 55 Location: San Francisco, CA
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Posted: Wed Jan 27, 2021 4:31 pm Post subject: Re: Coolant Temp Gauge Rebuild w/parts list & photos |
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Awesome! So glad to see someone else swinging for the fences.
I double checked your work. The polarity of your LED looks correct as are the directions of the diodes and op-amp and the value and position of your resistors. I can't tell from the photo if the cap is in the correct orientation.
NorthOf50 wrote: |
the LED didn't work before and doesn't now. |
I would guess that your issue may not be in the gauge, or at least not the electronics of the gauge.
If it is in the electronics there are four things I don't know: if the different type of cap you used is ok to use, the orientation the cap was soldered in, the specs of your new LED and if that will affect the circuit, the soldering work on the other side and whether you have a short or a bad connection.
Do you have a photo of the other side?
Is the cap in the right way?
Can you test the old LED to see if it works and if so, solder it back in place to test?
I have a bunch of leftover "audio quality" caps and could mail you one or two if you want. _________________ @tintopcamper
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NorthOf50 Samba Member
Joined: October 13, 2020 Posts: 102 Location: Campbell River, BC
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Posted: Thu Jan 28, 2021 11:57 am Post subject: Re: Coolant Temp Gauge Rebuild w/parts list & photos |
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ok. I have verified everything on my board. the cap polarity is correct. have traced out the circuits going on photos on the board empty. verified the gauge needle works as it should by pulling the coolant level probes, it pegs.
led still does not blink under any circumstance!!! argh.
"if" my circuit trace is correct. the LED should blink @ ign on via:
10V in, straight through LED, through the 150k resistor, charge up the 10uF cap then direct path through gauge ground (connector 14/5).
Things I know:
-10V in is good from voltage stabilizer
-gauge ground is good both through foil and gauge (tested and jumpered)
-cap is soldered w/ correct polarity
ideas?
_________________ '84 1.9WBX Camper (Penny)
'88 2.1WBX Camper (Martin) |
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fxr Samba Member
Joined: December 07, 2014 Posts: 2319 Location: Bay area CA
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Posted: Thu Jan 28, 2021 12:19 pm Post subject: Re: Coolant Temp Gauge Rebuild w/parts list & photos |
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The flashing should done by the 741, configured as an oscillator. You'll need to draw out the circuit diagram to work out how this circuit is supposed to perform.
I've googled for such a diagram, and it seems no-one has published it yet in a discoverable form!
To help, here's the components and the PCB (flipped) to make it easy:
It I can find a round tuit (in short supply here ATM) I'll have a stab at it myself... _________________ Jim Crowther
1984 1.9l EJ22 Westy Wolfsburg Edition
Vespa GTS 300 |
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MarkWard Samba Member
Joined: February 09, 2005 Posts: 17110 Location: Retired South Florida
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Posted: Thu Jan 28, 2021 12:20 pm Post subject: Re: Coolant Temp Gauge Rebuild w/parts list & photos |
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It looks overly complicated to me. Looking at the manual, the warning light is getting a chassis ground via cluster track "S" which terminates at the T 14 connector. Perhaps, its an external problem to the actual gauge. _________________ ☮️ |
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NorthOf50 Samba Member
Joined: October 13, 2020 Posts: 102 Location: Campbell River, BC
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Posted: Thu Jan 28, 2021 12:25 pm Post subject: Re: Coolant Temp Gauge Rebuild w/parts list & photos |
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I've been down the road of chasing the external ground already, before I rebuilt the gauge going so far as to running a ground wire directly from the rear of the gauge to a ground on the body. The 14pin track is actually "5" which shares the ground for the high beam indicator, which in my case works (now that I replaced the burnt out LED there).
I'm working with a colleague to try and trace out the entire circuit. Hopefully we'll get somewhere or if anyone else out there has further insight or locates a "round tuit" we can add to the collective knowledge here.
For those that are in the "know" are we certain that the LED blinking (at all points or any) is controlled by the gauge? Apart from sending a signal to peg the gauge, does the relay (43/42 - low lvl warning control unit) have anything to do with lighting the LED? I have a 43 in my van. It pegs the gauge. _________________ '84 1.9WBX Camper (Penny)
'88 2.1WBX Camper (Martin)
Last edited by NorthOf50 on Thu Jan 28, 2021 12:37 pm; edited 1 time in total |
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MarkWard Samba Member
Joined: February 09, 2005 Posts: 17110 Location: Retired South Florida
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Posted: Thu Jan 28, 2021 12:34 pm Post subject: Re: Coolant Temp Gauge Rebuild w/parts list & photos |
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I think you need some rope, sulfur, charcoal and a section of bamboo. _________________ ☮️ |
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