Many of the wiper problems we see in our cars can be easily corrected by replacing bad capacitors on the pulse wipe controller board.
If you've got "phantom wipes" or the wiper delay doesn't seem to have much (if any) control over the delay interval, then this is your cure.
The pulse wipe controller contains 4 aluminum electrolytic capacitors. These parts have a useful lifetime of less than 10 years; their seals fail and they dry out. Replacing these capacitors will return your wipers to "like new" operation.
Here's the parts to change:
You should be able to buy all of these parts at your local electronics store for less than $5. Solder the new parts in with the negative (short) lead towards the side of the board. If you don't have a soldering iron or don't know how, check with your local TV repair shop - they'll probably do it for you for a very small fee.
In any event, it's much better than installing another old board (same problem) or buying a new wiper motor (board no longer available separately).
NOTE: If you find burned traces on the back of this board it's because your wiper motor is defective. Replace the whole thing, don't try to patch the board. That trace is thin there on purpose; it's a fusible link to prevent a fire if the motor windings short out.
If they only live 10 years, that means all electronics containing electrolytic caps that are over 10 years old are bad?! Wouldn't that mean that everyone's ECM is bad also? Not trying to be negative, but I can't remember hearing that before... Are they just cheap caps, or do you mean all electrolytics in general?? I've got quite a few pieces of electronics that have over 10 year old caps, and still working good...?
------------------ Bob Williams Multi-colored '87 Mutt, a work in progress! (3800SC installation in super-super-ssuuppeerr-slow-motion progress... Done for Kansas? Riiiiiiiight....)
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10:29 PM
Whuffo Member
Posts: 3000 From: San Jose, CA Registered: Jul 2003
In addition to that, I find that the trace on the board also fries if your wiper switch in the column is shorting out as well...
I just checked the wiring diagram again and what you say is possible if the switch fails in a certain way. The positioning of the fusible link indicates it was to protect the motor windings, though...
By the way, one of the functions of the pulse wipe board is to "debounce" switch closures on the control stalk. So that "one wipe when I hit the turn signal" syndrome requires both the wiper switch to be a little flaky and the debounce circuit on the board to be inoperative. Fixing just the board will cure the problem; it'll ignore brief signals from the stalk / switch when it's working right.
Much easier than changing the wiper switch...
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10:30 PM
Whuffo Member
Posts: 3000 From: San Jose, CA Registered: Jul 2003
If they only live 10 years, that means all electronics containing electrolytic caps that are over 10 years old are bad?! Wouldn't that mean that everyone's ECM is bad also? Not trying to be negative, but I can't remember hearing that before... Are they just cheap caps, or do you mean all electrolytics in general?? I've got quite a few pieces of electronics that have over 10 year old caps, and still working good...?
Stop by any electronic repair shop and ask if old electrolytic caps go bad. You'll get an earfull...
Depending on what the cap is being used for, a radical decrease in value may or may not cause operational problems. If they're just decoupling caps (like the ones in the ECM) you could probably lose half of them and never miss them. These cheap electrolytic caps (yes, they are indeed cheap) have a wide tolerance when new (+80%, -20%) so designers take that into account.
The average lifetime given by their manufacturers is 7 to 10 years - some which live in comfortable surroundings live longer, some which live in hostile surroundings die much sooner.
In circuits like the pulse wipe board, their value is more critical. They're part of RC time circuits; the debounce ciruit, the pulse generator, and the asymmetric multivibrator that sets the delay cycle. And they live in a pretty hostile environment, so failures at this late date are unsurprising.
If you refer back to the picture, going from left to right the caps are (15 uf) debounce, (1 uf) pulse generator, (1 uf and 330uf) asymmetric multivibrator. If you get phantom wipes, it's probably the debounce cap. If on delay wipe the wipers just wiggle but never go through a full wipe it's probably the pulse generator cap. If the delay wipe is goofy, the multivibrator caps are suspect - they'll also cause phantom wipes when they go bad.
Why would GM use cheap caps? For small capacitors with high values, these cheap aluminum electrolytics work well enough and are 1/10th the price of anything else with comparable performance. Not just GM but virutally all electronics manufacturers use these little devils...
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10:44 PM
Riceburner98 Member
Posts: 2179 From: Natick, Ma, USA Registered: Apr 2002
Aaaah, got ya. Things they don't teach you in skool. LOL Thanks for the lesson... Something to remember! I guess I'm just used to working on new electronics, mostly with Tantalums at that... Only caps I normally see are in the power supply, which wouldn't be bothered as much by degredation.. Did you get a schematic for the wiper board, or just reverse-engineer it?
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10:55 PM
Sep 7th, 2004
Whuffo Member
Posts: 3000 From: San Jose, CA Registered: Jul 2003
Aaaah, got ya. Things they don't teach you in skool. LOL Thanks for the lesson... Something to remember! I guess I'm just used to working on new electronics, mostly with Tantalums at that... Only caps I normally see are in the power supply, which wouldn't be bothered as much by degredation.. Did you get a schematic for the wiper board, or just reverse-engineer it?
I "reverse engineered" it. It's a fairly simple piece; basic analog circuitry. I thought about replacing the bad caps with tantalums - but heck, the aluminum caps are so inexpensive and if they go bad in another 10 years I'll just replace them again (grin). Other than the cheap caps, I was impressed with the quality of this assembly. Nice epoxy PC board, silkscreened component IDs, nice solder work; if it had tantalum caps on it it'd be mil spec.
This board was clearly not made by the same people that made the blue ding thing - that thing isn't very nicely built at all. One of these days I'll rebuild that thing too so that it works the way it was supposed to...
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01:04 AM
cptsnoopy Member
Posts: 2585 From: phoenix, AZ, USA Registered: Jul 2003
my washer pump was iffy at best and now it does not work. assuming it is not getting power would any of these cap replacements help that? is there a relay i should be replacing? thanks for the fix info, + to you!
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01:22 AM
Vonov Member
Posts: 3745 From: Nashville,TN,USA Registered: May 2004
I gave you a plus, too, Whuffo. Great talent you have there, thanks for sharing it with the rest of us. Which reminds me...how difficult would it be to remote-mount our ignition modules with the objective of putting them in a cooler location, maybe with a big heat sink/fan attached, to give them better reliability/longer life?
Tony (didn't mean to hijack thread, I'll post the question separately) ------------------ 88 Formula, "Asphalt Aviator"
"I've seen em---they're little fellers. You know, the Artesians..." ---caretaker at Olympia Brewery
[This message has been edited by Vonov (edited 09-07-2004).]
my washer pump was iffy at best and now it does not work. assuming it is not getting power would any of these cap replacements help that? is there a relay i should be replacing? thanks for the fix info, + to you!
Same thing here.....
I have to replace those caps... Just recently my delay wipers have been getting really goofy!
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11:43 AM
PFF
System Bot
webbee Member
Posts: 1149 From: Los Angeles, Ca. USA Registered: Jun 2000
Abit, A-open, MSI have all had problems with PC motherboard capacitors leaking after a few months of use. I'm surprised that GM capacitors have lasted 10 years. Great tip by the way. Military and space grade parts last a lot longer. If you can find them surplus they are cheap and really good quality.
Note that this site suggests that more than one circuit board was used, and that the value of some of the electrolytic capacitors in the '88 schematic differ from Whoffo's original post. No problem; just replace your electrolytic caps with the appropriate (i.e., same) value.
Mark
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07:30 PM
Whuffo Member
Posts: 3000 From: San Jose, CA Registered: Jul 2003
my washer pump was iffy at best and now it does not work. assuming it is not getting power would any of these cap replacements help that? is there a relay i should be replacing? thanks for the fix info, + to you!
Are you sure the fuses are good? If so, what happens when you hit the washer tab? Do the wipers come on for a few cycles? If the wipers come on then the pulse board is working and the problem is most likely the washer pump. If you get no wipe or wash then you may have a bad wiper switch. Bad caps on the pulse board won't keep the washers from working in any event.
Replacement pumps are available from your local parts store for about $15. This is a common problem...
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07:34 PM
Whuffo Member
Posts: 3000 From: San Jose, CA Registered: Jul 2003
Note that this site suggests that more than one circuit board was used, and that the value of some of the electrolytic capacitors in the '88 schematic differ from Whoffo's original post. No problem; just replace your electrolytic caps with the appropriate (i.e., same) value.
Mark
I checked the schematic on that site and it's different than the board I have. There may be several revisions, but as you say just replace the electrolytic caps and it should be good. The exact value of the caps isn't super critical, either - if you can't find the exact value, the next size larger will work fine.
Thanks for the lesson... Something to remember! I guess I'm just used to working on new electronics, mostly with Tantalums at that... Only caps I normally see are in the power supply, which wouldn't be bothered as much by degredation.. Did you get a schematic for the wiper board, or just reverse-engineer it?
