73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Electrical => Topic started by: Wickman on January 31, 2019, 05:03:15 AM
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Hi all
I'm new here and I really enjoy to see how many we are that loves these trucks. I really like to work with my 1983 C20 Silverado with 6,2 l diesel. I'm just about to finish my one year frame of restoration work and at present I'm installing the electrical harness again. An improvement I would like to add is a delay module to the wipers. I found one here at the local junk yard but the pulse-mode don't work (all other operation modes work fine, but not the pulse). I have a new switch - they are easy to find - but I have really search for a new delay module, without success. The ones for 84 and up can be bought several places, but I cant find any for 183 an earlier.
Anyone who have an idea where I may find such a one?
Thank you all for all good info.
Andreas Wickman Sweden
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Try this https://www.classicindustries.com/product/sw607.html
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Thank you for tip, but as far as I can see they just offer the switch (which I already have) - Í miss a working delay module (connected between the switch and harness). I guess it is some electronic part broken in mine.
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Ahh, you'll have to keep your eyes open for one, as far as I know they are not reproduced. Aftermarket is another option. there are universal fit ones on the market.
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That wouldn't be hard to take apart. My 87 hade the larger module that did not work. I took it apart and found a couple of cold solder joints. Fixed those and good to go. Might try it worth a shot. If you feel uncomfortable soldering find someone that repairs computers. They are usually good at soldering small circuits.
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Check the link below. I think it is a universal model and may/may not work for your application. Review the write-up from Scott regarding his installation.
https://store.qkits.com/wind-shield-wiper-timer-module-mxa041.html
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Regarding an attempt to repair it. Yes, it is very easy to open the black box, but inside its more components on that circuit board than one can understand why its necessary to have all these. No visible faults observed. It should be possible to repair it, but to be able to manage that I guess its necessary to understand how the circuit is meant to work. It seems like I have to keep looking for a used one that works.
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"Repairing" a pulse module is a matter of replacing all of the electrolytic capacitors on the circuit board. This is because electrolytic capacitors are manufactured with a wet electrolyte that dissipates and dries over time, making the capacitors ineffective. If you elect to do this, replace one at a time using new capacitors (caps) that have the same capacitance and voltage specifications as the originals. Electrolytic capacitors are polarized. Pay close attention to polarity markings (+/-) on the original caps before removing them from the board, then install the replacements in the exact same polarity orientation; otherwise, they short circuit and fail, sometimes violently.
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I just say "Wow". I'm deeply impressed and glad. That's knowledge! I do like the idea of repairing things instead of just throw them away. Perhaps that view is a little of the base for all of us who loves these old trucks, keep them, restore them.
Anyhow, are you so familiar with this item that you also have an idea why there is what I think looks like an IC-circuit in the middle of the circuit board? And do you no how the resistor circuit (the one you alter with the turnable knob on the switch) get positive voltage, which as I understand it must be present to make the current flow.
Andreas
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Effectively, the IC comprises a timer circuit, much like an LM555 or LM556. The variable resistor (potentiometer) adjusted via the turn signal stalk, works in conjunction with one of the board capacitors to form an RC network that charges according to a time constant that is determined by the resistance of the potentiometer in relation to the capacitor value. When the capacitor of the RC network is sufficiently charged it triggers the IC into a monostable mode that switches on the power transistor to pulse the wiper motor. At that point, the park switch in the wiper motor takes control of the motor allowing the wiper to complete one sweep before parking.
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I can see you really know how this item works. like you were the designer. You have now convinced me, I have a buddy who makes modified computers, I will ask him to replace all (three?) capacitors. I will of course let you know the result.
Your deep insight made me curious. How can it be that you know so much about this device?
Its late now on this side of the globe. I will go to bed (so no more writing from me tonight)
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Circumstances forced the solution. I had several modules that didn't function and were no longer available for purchase. At the time, my only recourse was to repair them. Upon close inspection with a bright light and magnifier, I observed trace fluid stains beneath every capacitor. The rest is history. :)
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Mind if I use your term; "Circumstances forced the solution"?
It applies to so many areas of life...
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I found this video on youtube https://www.youtube.com/watch?v=szUOZ0eCUtM&t=186s
The "frosty" item in the middle of the board, what is that?
Luckily the one on my board looks better.
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That is the power transistor that switches motor current. The "frosty" white stuff is heatsink compound and is crucial for transistor longevity. The compound ensures efficient heat transfer between the transistor and the finned aluminum heatsink in the module case. Inspect the PC board solder joints using a 10X hand magnifier. If any solder joints appear to be cracked, resolder using electronics grade, silver-bearing solder and a 5 - 7-watt pencil soldering iron. Resolder ONLY joints that appear to be cracked, if any, so that you don't risk overheating and damaging silicon components (e.g., IC, transistor & diodes).
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Shall I understand it as the compound shall be there in order to transfer heat? My transistor don't have that, see pic, so shall I now suspect the transistor to be "burned"? Can such a one be checked? I cant see any spec on it (perhaps on the back side?). The transistor is laying on a piece of white plastic/nylon.
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Replace the caps and smear a thick coat of heatsink compound on the exposed upper surface of the power transistor then reinstall the PC board into its case and test the module operation. The thick nylon sheet below the power transistor is a shim to help press the transistor against the aluminum heatsink.
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I see. A big thank you for excellent assistance. You must be a professional automobile expert, not just an interested hobby enthusiast. I have read several of your posts here on the forum, and it is a true pleasure and very educating.
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Thanks. I appreciate that.
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So now with all capacitors new on the board... No, still the same Four out of five operations work (Mist - holding knob to the left - Works, OFF Works -wipers park in right position- LO works, HI works). Pulse/delay DONT:
But there is something that I don't understand. The circuit with the resistor, how can it be any current running through that circuit? There is no positive lead to the delay module (except the one for light bulb). The entire wiper control is just handling ground connections, positive voltage goes directly from fuse box to wiper motor and washer rely.
And another clue that indicates that I am missing something is the sentence I read under the header "DELAY WIPER SYSTEM OPERATION AND DIAGNOSIS" in the Shop manual for 10-30 lighy duty trucks. There is a sentence (with no explanation) that says: "There is also a lead from the control that plugs into the accessory cavity of the fuse panel". No more about that wire, just that. And on the electric wire diagram no such lead is showed, and there is definitely no such wire on my module.
Question remain: Where is the voltage level that push current through the variable resistor circuit?
Very curious if someone can answer this.
Andreas Wickman
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Did you actually measure the variable resistor to see if it actually varies when turning the knob?
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No I haven't, but that was exactly what I was thinking could be next step. But even if that test shows that the resistance do varies while turning the knob, I think my question remains; how can the delay module work without any positive connection? Also loading the capacitors - how?
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I believe the module in your truck is a newer generation than that described in your manual. Older pulse modules used a miniature electromechanical relay that is absent from the PCB of your module. The dedicated power lead was used on the older modules with relays. I think on the newer modules power is acquired through the high-speed circuit from the motor(?). I will need to study the wiring diagrams further to verify this idea when time is available.
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Ok, an older version can be an explanation. Regarding supply of positive voltage to charge capacitors and to create a current flow in the varistor circuit I am now quite convinced it's coming to the module via the wash-trigger-coil. I have made a test rig and a clear wiring diagram. I will not leave this before I got it to work!
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interesting that you bring that up. On my 87 that has the turn stalk wipers and module at bottom of column, If I have the connector to the washer pump which is mounted on the back of the reservoir disconnected my delay wont work.
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Well that's a proof that there is where the positive voltage come from.
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:) GOOD NEWS, my delay module are fit for fight again. It was the tyristor that was broken. Perhaps overheated because it was lack of heat-transmission over to the aluminium fine-block when there was no heat sink compound upon the old tyristor.
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That's great news. Very well done! Do you have the part number of the component that failed?
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It was my "Computer-buddy" who had it in his "good-to-have-box". It was a true standard component he said, so I have e-mailed him now for the part number. I will forward it as soon as I got it. Further he said that also the IC was a true standard component easy to find (and so of course all the resistors also). This means that as long as you have circuit board intact, you are able to fix it. GOOD!
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I'm glad you got it working. This experience has probably given you a good insight on how the whole system works by researching and dissecting components. These days it's just remove old part and replace with another with no real clue on how things operate or why things fail. I come from old school were we repaired components instead of replacing them. On my own 87 the wipers were real slow so I was bound and determined to repair it. I peeled open the end of the motor and removed the armature. Cleaned up all the old and stiff grease out. Relube it and reassembled. Works as good as new. Now I have a better understanding on how it all works.
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I do agree completely, and guess that this "mentality" - to see a great value in repairing things instead of just throw away and exchange - is one thing that unite us who love these old trucks. It is possible to repair and understand them. Important for life quality i think.
This experience with the delay module - to repair an electronic devise - was however completely new and it was all thanks to Senior Moderator bd on this page. When I realized that it was an what I judge as an "electronic component" that didn't work my thought was that the only way to come further was to find a new one, but at that stage bd came in and just just methodical gave instructions how to proceed. The clear way he described the process gave me a whole new view on such component. And when I then showed it to my computer buddy (same age as me) he said that all component on the circuit board was standard component he has in his workshop. He said that was the good thing with these electronic devices from the 80-ties, just standard components - easy to find and cheap.
All the best!
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The broken tyristor we used were manufactured by a company called NXP. Part # BT145-800R. Price: 2 USD. Yes you see, to repair is cheap, but you need knowledge.
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You are very gracious, Mr. Wickman. Thank you. I learned a few new things during this exercise as well.