Home » Public Forums » GMCnet » [GMCnet] Broken 1227747 ECM
| [GMCnet] Broken 1227747 ECM [message #61206] |
Thu, 22 October 2009 18:38  |
GMCWiperMan
Messages: 1248
Registered: December 2007
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Has anyone found a schematic for the 1227747 ECM? Not for connecting it
to the outside world -- its guts.
Some may recall that I had a Holley fuel injector apparently fail
recently. When I replaced it, the new one would not shut off until I
changed the ECM for the one I'd just modified for the EBL Flash board.
Not knowing whether the failed injector damaged the ECM or the failed
ECM damaged the injector is not a comfortable position to be in. Don't
know what to expect next.
Today I checked the resistance of the "failed" injector -- about 2 Ohms
which is in spec. But I couldn't hear it click when I applied 5 VDC or
12 VDC. I suspect it's been sticking for a long time. I've read
reports that Holley's preservative for them sometimes causes them to
stick when new.
Then I opened the '7747. Right away I realized that I have a hard
failure there: CR25, a 1-6 amp diode, PN as yet unknown, is cooked. To
the extent that it's almost melted its solder joints into the PC board.
I don't see any board damage beyond that. But, it's a single diode, not
one of a set of 4 as it would probably be if it was a part of the quad
drivers for the injectors, so I can't even speculate how it was
subjected to such excessive current. Spontaneous failure is extremely
unlikely.
I sure don't want to have to reverse engineer the board in order to
figure out what caused the failure. It may have been something I
inadvertently did while troubleshooting. Even worse, it may NOT have
been something I did. I can prevent repeating my own errors, but I
can't fix something else if I don't know what to fix -- so a repeat
could be imminent. Replacing the ECM is not a good option with my
current lack of understanding of the failure.
Surely someone, somewhere, has reverse engineered or otherwise acquired
a schematic for the board. Any ideas out there?
Ken Hating Hardware w/o Schematics H.
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| Re: [GMCnet] Broken 1227747 ECM [message #61239 is a reply to message #61237] |
Thu, 22 October 2009 21:51  |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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The schematics seem to prove that I damaged the ECM myself. CR25 Zener
Diode is directly across output lines D15 & D16 -- one of the injectors
-- undoubtedly the one that "failed" -- I'll have to verify that
tomorrow. If I inadvertently applied 12 VDC to that line, it would fry
the Zener because there's no current limiting between the injector
connector and that diode, which is probably there to protect the output
transistor from the inductive kickback from the injector.
Also, if that diode shorted, as it should have failed, it would turn the
injector on, giving the continuous injection I saw when I installed the
new injector with this ECM.
On the other hand, if the injector shorted, it would have the same
effect. MAYBE I didn't do it myself. I'll have to check the failed
injector more carefully tomorrow.
Without having examined all of the schematics, I'm now curious about the
continual references to a Quad driver -- I don't see but two, though
they connect to four lines. Maybe that's how they come up with "Quad".
I'd expected a Quad Driver IC.
Thanks again, Dave. I'll sleep better tonight.
Ken H.
Ken Henderson wrote:
> Dave,
>
> Thanks a BUNCH! That's it. There's CR25 in the Right Injector
> circuit. I haven't traced it yet but with this maybe I can at least
> figure out whether the injector or the board failed first. That will
> relieve my mind whether I repair the ECM or just replace it.
>
> Bruce, you can quit searching -- the MASTER RESEARCHER came through
> again! :-)
>
> Ken H.
>
> Dave Mumert wrote:
>> Hi Ken
>>
>> Try here
>> http://www.exatorq.com/ludis_obd1/schematics.html
>>
>> Apparently the 1228746 uses the same board as the 1227747
>> Here is the output section
>> http://www.exatorq.com/ludis_obd1/1228746sheet5.gif
>>
>> Dave
>>
>>
>>
>> -----Original Message-----
>> From: gmclist-bounces@temp.gmcnet.org
>> [mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Ken Henderson
>> Sent: Thursday, October 22, 2009 5:39 PM
>> To: gmclist@temp.gmcnet.org
>> Subject: [GMCnet] Broken 1227747 ECM
>>
>> Has anyone found a schematic for the 1227747 ECM? Not for connecting
>> it to the outside world -- its guts.
>>
>> _______________________________________________
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Broken 1227747 ECM [message #61268 is a reply to message #61206] |
Fri, 23 October 2009 08:21 |
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RF_Burns
Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada
Karma: 3
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Ken,
The Zener CR25 would have a zener voltage well above 12V. The injector output from the ECM is an "open collector" output. If your injector was shorted it would not harm the CR25 (provided the vehicle voltage was not above the zener voltage which it should not be), but it would have toasted the output transistor and emitter resistor R80.
In the mobile radio world I typically see zeners in this type of application rated between 18-27 volts. IF your vehicle voltage went above the zener voltage then the diode would have started to conduct and depending on the diode's rating may have shorted.
Since we know the diode is toasted, either the vehicle voltage exceeded the zener voltage to the point where the zener current then exceeded the diode's rating... OR its a 20 some year old diode and it was just its time to go. Since its got really hot it did not short completely.
About the only thing that would make your vehicle voltage rise fairly high is a faulty alternator, or a fault in the battery voltage sense line going to the alternator.
And since the other injector driver diode seems fine, (over voltage should have damaged it too), I'm thinking that CR25 just had a bad day and started to break down. It did not short completely leading to alot of power dissipation (heat) which has damaged the board.
Remove the zener diode and put a trouble-light from +12v to that Injector output and hook ground to the ECM ground. The lamp should stay OFF if the driver transistor is Ok. If so get a 20V 3-5 watt zener ( there are also special zener's for this application) from Digikey and plug it in and see what happens.
Well, after all that I'm guessing you likely know all that and more!
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
[Updated on: Fri, 23 October 2009 08:25] Report message to a moderator |
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| Re: [GMCnet] Broken 1227747 ECM [message #61274 is a reply to message #61268] |
Fri, 23 October 2009 09:01 |
Surbo
Messages: 213
Registered: February 2004
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| RF_Burns wrote on Fri, 23 October 2009 08:21 |
Ken,
The Zener CR25 would have a zener voltage well above 12V. The injector output from the ECM is an "open collector" output. If your injector was shorted it would not harm the CR25 (provided the vehicle voltage was not above the zener voltage which it should not be), but it would have toasted the output transistor and emitter resistor R80.
In the mobile radio world I typically see zeners in this type of application rated between 18-27 volts. IF your vehicle voltage went above the zener voltage then the diode would have started to conduct and depending on the diode's rating may have shorted.
Since we know the diode is toasted, either the vehicle voltage exceeded the zener voltage to the point where the zener current then exceeded the diode's rating... OR its a 20 some year old diode and it was just its time to go. Since its got really hot it did not short completely.
About the only thing that would make your vehicle voltage rise fairly high is a faulty alternator, or a fault in the battery voltage sense line going to the alternator.
And since the other injector driver diode seems fine, (over voltage should have damaged it too), I'm thinking that CR25 just had a bad day and started to break down. It did not short completely leading to alot of power dissipation (heat) which has damaged the board.
Remove the zener diode and put a trouble-light from +12v to that Injector output and hook ground to the ECM ground. The lamp should stay OFF if the driver transistor is Ok. If so get a 20V 3-5 watt zener ( there are also special zener's for this application) from Digikey and plug it in and see what happens.
Well, after all that I'm guessing you likely know all that and more!
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Ken & Bruce;
Would not the 'check engine' light come on when this was going on? Sometimes it would have shown a QDR code, depending on the type of QDR used in the ECM. Just to add some more info, GM used at least three styles of QDR's, for different vehicles and different applications. (SFI or TBI,etc) The QDR's had improvements as the years progressed. OBD I '91-'93 had the QDR II in the 5.7L.
1.Quad drivers (QDR)
Are permanently damaged if a device or its circuit shorts, no added circuit protection.
2.Quad drivers II
Temporarily shut down and then reset if a device or its circuit shorts.
3.Quad driver modules (QDM)
Temporarily shut down, sets a fault code, and then resets if a device or its circuit shorts.
Bob Drewes in SESD
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| Re: [GMCnet] Broken 1227747 ECM [message #61279 is a reply to message #61268] |
Fri, 23 October 2009 09:17 |
GMCWiperMan
Messages: 1248
Registered: December 2007
Karma: 1
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Bruce,
Now that I'm awake, I agree with you -- I was thinking the Zener voltage
was <<12 V, which is, of course, absurd. Your logic makes perfect sense
in the light of day. But I've never seen a Zener "age out" before.
However, I'm sure the system voltage was not the culprit; as you say,
the other driver should have been affected also, but more than that, so
should a lot of other equipment.
I'll get finished with other chores soon and get back to the electronics
work bench.
Ken H.
Bruce Hislop wrote:
> Ken,
> The Zener CR25 would have a zener voltage well above 12V. The injector output from the ECM is an "open collector" output. If your injector was shorted it would not harm the CR25 (provided the vehicle voltage was not above the zener voltage which it should not be), but it would have toasted the output transistor and emitter resistor R80.
>
> In the mobile radio world I typically see zeners in this type of application rated between 18-27 volts. IF your vehicle voltage went above the zener voltage then the diode would have started to conduct and depending on the diode's rating may have shorted.
>
> Since we know the diode is toasted either the vehicle voltage exceeded the zener voltage to the point where the zener current then exceeded the diode's rating... OR its a 20 some year old diode and it was just its time to go. Since its got really hot it did not short completely.
>
> About the only thing that would make your vehicle voltage rise fairly high is a faulty alternator, or a fault in the battery voltage sense line going to the alternator.
>
> And since the other injector driver diode seems fine, (over voltage should have damaged it too), I'm thinking that CR25 just had a bad day and started to break down. It did not short completely leading to alot of power dissipation (heat) which has damaged the board.
>
> Remove the zener diode and put a trouble-light from +12v to that Injector output and hook ground to the ECM ground. The lamp should stay OFF if the driver transistor is Ok. If so get a 20V 3-5 watt zener ( there are also special zener's for this application) from Digikey and plug it in and see what happens.
>
>
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| Re: [GMCnet] Broken 1227747 ECM [message #61284 is a reply to message #61279] |
Fri, 23 October 2009 09:53 |
Tin Gerbil
Messages: 236
Registered: October 2006
Location: Vancouver Island, B.C.
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Ken;
Bruce's logic must be faulty. My solution was to offer you $5.00 for
your 7747 to relieve you of any further anguish. Now for $1.00 you must
sweat and toil over a terminally ill ECM, only to return it to
questionable value. I bet you will even carry it as a spare, weighing
down your poor little 23' and even more straining that dangerously weak
4-bag system. Do you worry about the increase in stopping distance from
the weight of more spares?
Do you use Newark Electronics?
Gordon
Ken Henderson wrote:
> Bruce,
>
> Now that I'm awake, I agree with you -- I was thinking the Zener
> voltage was <<12 V, which is, of course, absurd. Your logic makes
> perfect sense in the light of day. But I've never seen a Zener "age
> out" before. However, I'm sure the system voltage was not the
> culprit; as you say, the other driver should have been affected also,
> but more than that, so should a lot of other equipment.
>
> I'll get finished with other chores soon and get back to the
> electronics work bench.
>
> Ken H.
>
> Bruce Hislop wrote:
>> Ken, The Zener CR25 would have a zener voltage well above 12V. The
>> injector output from the ECM is an "open collector" output. If your
>> injector was shorted it would not harm the CR25 (provided the
>> vehicle voltage was not above the zener voltage which it should not
>> be), but it would have toasted the output transistor and emitter
>> resistor R80.
>>
>> In the mobile radio world I typically see zeners in this type of
>> application rated between 18-27 volts. IF your vehicle voltage
>> went above the zener voltage then the diode would have started to
>> conduct and depending on the diode's rating may have shorted.
>>
>> Since we know the diode is toasted either the vehicle voltage
>> exceeded the zener voltage to the point where the zener current
>> then exceeded the diode's rating... OR its a 20 some year old diode
>> and it was just its time to go. Since its got really hot it did
>> not short completely.
>>
>> About the only thing that would make your vehicle voltage rise
>> fairly high is a faulty alternator, or a fault in the battery
>> voltage sense line going to the alternator.
>>
>> And since the other injector driver diode seems fine, (over voltage
>> should have damaged it too), I'm thinking that CR25 just had a bad
>> day and started to break down. It did not short completely leading
>> to alot of power dissipation (heat) which has damaged the board.
>>
>> Remove the zener diode and put a trouble-light from +12v to that
>> Injector output and hook ground to the ECM ground. The lamp should
>> stay OFF if the driver transistor is Ok. If so get a 20V 3-5 watt
>> zener ( there are also special zener's for this application) from
>> Digikey and plug it in and see what happens.
>>
>>
>
> _______________________________________________ GMCnet mailing list
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Gordon
'74 Canyon Lands "Tin Gerbil"
Vancouver Island, B.C.
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| Re: [GMCnet] Broken 1227747 ECM [message #61285 is a reply to message #61206] |
Fri, 23 October 2009 10:00 |
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RF_Burns
Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada
Karma: 3
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Ken,
I guess I should have said that no semiconductor is perfect and who is to say why it went faulty... Maybe a spike from the starter motor windings etc, It's job was to protect the transistor which I guess it did!.
I looked up the driver chip (LM1949), and then the data sheet. It calls for a 33V, 5watt zener. Looking in Digi-Key there is a 5KP30ALFCT. They are purpose built zener's called Transient Suppression diodes.
Bob,
It would appear from the schematics that the 7747 used discrete parts for driving the injectors rather than a specialty driver module.
See schematic here:
http://www.exatorq.com/ludis_obd1/1228746sheet5.gif
There is no sensing of the injector output back to the micro for monitoring of any problems. I'm guessing the quad driver modules in other ECM's gave feedback to the microprocessor to monitor any problems.
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
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| Re: [GMCnet] Broken 1227747 ECM [message #61392 is a reply to message #61285] |
Fri, 23 October 2009 20:24 |
GMCWiperMan
Messages: 1248
Registered: December 2007
Karma: 1
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Bruce,
I'm coming around to your assumption that the Zener died a natural
death. Its body and the surrounding area looked bad before I removed
it. Then it looked REALLY bad. The board is burned down into the
fiberglass -- top and bottom. But nothing outside the radius of the
heat from the Zener shows any damage. The body of the Zener is not
ruptured as I've usually seen when a sufficiently high surge to cause
that much collateral damage occurred. I think it just sat there and
cooked for a long time before finally shorting completely.
The driver transistor is not shorted so I ordered a couple of the
DigiKey transient suppressors you found -- thanks for that and all the
research it took to find them. The markings on CR25 were mostly legible
but did not correlate to anything it could have been.
Thus far I've found nothing different between the drawings and the
1227747 I have. It came from Howell with my EFI kit so I have no idea
what vehicle it was in originally. You're right, this one has no
feedback to the CPU from the actual output.
The one thing that's surprised me is the lack of symmetry between
identical circuits. The component layouts bear no similarity to each
other so there's no looking at the board and guessing at functions.
Today stimulated some long-unused brain cells; Thinking I'd use it to
test the diode, and possibly the driver transistors, I dug out the dual
channel transistor curve tracer I built in 1973. And the long-unused
oscilloscope that sits covered on the workbench to use to view the
curves. No telling how much time I wasted trying to get that ancient --
can it really be 36 years ago!?!? -- gadget working. Finally did test
the diode using the curve tracer's variable high voltage output and the
'scope, but never got base current steps for transistor testing. Hardly
worth the trouble to remove the screws to get inside, so I'll set it
back on the shelf. Maybe one of the grandsons will want to tinker with
something Granpa won an IEEE contest with. :-)
Then I dipped a toe in much more modern electronics. My mother's
nursing home uses an ancient (probably older than my curve tracer)
wall-mounted nurse call system with pendant switches hanging from 1/4"
'phone plugs. When Mother broke her hip last year she had trouble
getting to the switch to call for help. So when she returned to
Assisted Living, I set up one of the little Tx/Rx remote relays
available for $11.50 to provide her with a necklace carried remote control.
When the nursing staff noticed it for the first time last week, they got
all excited, telling me what problems they have with carpet burns from
old folks crawling to the pendant, of people lying un-aided for hours
unable to call, etc.
So I ordered a dozen of the Tx/Rx relays, wall warts, and male-male 1/4"
'phone extension cords to make some for other residents. To ensure they
don't interfere, I had to reprogram all of the remotes. They use a
PT2662 IC encoder with tri-state inputs. That's where my modern
problems began -- had to remember how to count in ternary (trinary).
Then the REAL fun began. The coding pad array is about the size of an
SMT array -- too DARNED small for my eyes, even with reading glasses and
a magnifier lamp. And even when I finally got enough magnification to
sort of see the individual pads, I discovered that apparently on the
production line they just randomly create large solder bridges to set
random codes. After solder-wicking all those off, I found I'm not
steady enough to create the specific solder bridges I needed. :-( And I
had no wire strands small enough to stick into the holes in the pads.
Probably took me 15 minutes on each Tx just to solder two itsy-bitsy
pieces of wire on each board. Gotta be a better way. Maybe I'll get a
conductive pen for the next batch.
I'll let y'all know the results after I install and test the diodes in
the ECM.
Ken H.
Bruce Hislop wrote:
> Ken,
> I guess I should have said that no semiconductor is perfect and who is to say why it went faulty... Maybe a spike from the starter motor windings etc, It's job was to protect the transistor which I guess it did!.
>
> I looked up the driver chip (LM1949), and then the data sheet. It calls for a 33V, 5watt zener. Looking in Digi-Key there is a 5KP30ALFCT. They are purpose built zener's called Transient Suppression diodes.
>
> Bob,
> It would appear from the schematics that the 7747 used discrete parts for driving the injectors rather than a specialty driver module.
> See schematic here:
> http://www.exatorq.com/ludis_obd1/1228746sheet5.gif
>
> There is no sensing of the injector output back to the micro for monitoring of any problems. I'm guessing the quad driver modules in other ECM's gave feedback to the microprocessor to monitor any problems.
>
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| Re: [GMCnet] Broken 1227747 ECM [message #61451 is a reply to message #61426] |
Sat, 24 October 2009 11:49 |
GMCWiperMan
Messages: 1248
Registered: December 2007
Karma: 1
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Senior Member |
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In view of my mini-catastrophe, I guess I'd better check my other 3
diodes too.
If the knock counts you're seeing are like the ones I see, all over the
place, they're probably just random noise, input load resistor or not.
Is that function not switched off in the BIN, making the counts
irrelevant? Of course, without a CCD, they would be anyway, unless
there's some relationship to other tables that I haven't found.
Does the VSS have a 2000 ppm square wave output? If so, it will work.
Mine is 4000 ppm. 'Druber sent me a divide-by-two buffer to feed the
ECM. I have no idea where it is now, so I'll probably have to make
one. I'm sure I've got a 35+ yo flip-flop around somewhere. :-)
I should be EFI tinkering also, but instead I'm trying to figure out how
to mount the Troy-Bilt/Briggs & Stratton 5250W generator in place of the
crashed Generac.
Ken
Bruce Hislop wrote:
> Ken,
> I am going to take a quick look at the boards in both my ECM's and do a quick leakage test on the diodes just to be safe.
>
> Semi-conductors seem to be much more reliable now than they were even in the late 80's when these ECM's were likely made. At that time I had 5 Techs working for me, now I have only one.
>
> Looking at the schematic I can't fiqure out why I have knock counts. I had understood there was a module in the wiring harness to simulate knock counts. But the only module in my wiring harness is a buffer for the HEI spark input. The Knock sensor input is not connected and looking at the schematic it shows a resistor to ground on the knock input buffer. Unless that resistor is not pulling to ground and the buffer is picking up stray noise. I'll soon find out as I have the knock sensor module to connect today.
>
> First I'll tackle the VSS when I get back from the office. Hope i have the right one!
>
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| Re: [GMCnet] Broken 1227747 ECM [message #61454 is a reply to message #61451] |
Sat, 24 October 2009 11:57 |
Tin Gerbil
Messages: 236
Registered: October 2006
Location: Vancouver Island, B.C.
Karma: 0
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Ken Henderson wrote:
> In view of my mini-catastrophe, I guess I'd better check my other 3
> diodes too.
>
> If the knock counts you're seeing are like the ones I see, all over the
> place, they're probably just random noise, input load resistor or not.
> Is that function not switched off in the BIN, making the counts
> irrelevant? Of course, without a CCD, they would be anyway, unless
> there's some relationship to other tables that I haven't found.
Ken;
Any truth to the need for a "tuned knock sensor"? One specifically
designed for the engine. Kind of like not recognizing someone beating
on my head with a hammer because I'm listing to music?
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Gordon
'74 Canyon Lands "Tin Gerbil"
Vancouver Island, B.C.
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| Re: [GMCnet] Broken 1227747 ECM [message #61460 is a reply to message #61454] |
Sat, 24 October 2009 12:34 |
GMCWiperMan
Messages: 1248
Registered: December 2007
Karma: 1
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Gordon,
There are different knock sensors for different engines, but not very
many; they seem to be trying to standardize somewhat. But the early
ECM's like we use have external Electronic Spark Control (ESC) modules
which are for virtually every application. The ESC is the filter which
is tuned to the noise characteristics of the particular engine. I've
begun to see different numbers prescribed for the 454; I don't know how
much effect they really have on the knock counts seen by the EMC.
Ken H.
The Tin Gerbil, Ad Nauseum wrote:
> Ken Henderson wrote:
>
>> In view of my mini-catastrophe, I guess I'd better check my other 3
>> diodes too.
>>
>> If the knock counts you're seeing are like the ones I see, all over the
>> place, they're probably just random noise, input load resistor or not.
>> Is that function not switched off in the BIN, making the counts
>> irrelevant? Of course, without a CCD, they would be anyway, unless
>> there's some relationship to other tables that I haven't found.
>>
>
> Ken;
> Any truth to the need for a "tuned knock sensor"? One specifically
> designed for the engine. Kind of like not recognizing someone beating
> on my head with a hammer because I'm listing to music?
> _______________________________________________
>
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| Re: [GMCnet] Broken 1227747 ECM [message #61465 is a reply to message #61460] |
Sat, 24 October 2009 13:06 |
rvanwin
Messages: 325
Registered: April 2007
Location: Battlefield, MO
Karma: 6
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| GMCWiperMan wrote on Sat, 24 October 2009 12:34 |
Gordon,
There are different knock sensors for different engines, but not very
many; they seem to be trying to standardize somewhat. But the early
ECM's like we use have external Electronic Spark Control (ESC) modules
which are for virtually every application. The ESC is the filter which
is tuned to the noise characteristics of the particular engine. I've
begun to see different numbers prescribed for the 454; I don't know how
much effect they really have on the knock counts seen by the EMC.
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I have been concerned about the same issue. I seem to remember reading that the knock sensor/ESC is "tuned" based on the size of the cylinder. I have a '403'. I got my knock sensor and ESC from a 4.3 V6 which I think has similar cylinder characteristics as the 403. I see knock counts in my logs but sometimes I think I'm hearing some ping but not sure the ECM is backing off the timing. I'm now logging the total spark advance (using a patch) so maybe I can catch a situation where I get knock counts and can see if timing got retarded. I need some test time...
Randy & Margie
'77 Eleganza II '403'
Battlefield, MO
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