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Printed Circuit Board/Exciter Replacement Issues

 
Old 10-25-2008, 11:12 PM
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Chris Hansen
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Default Printed Circuit Board/Exciter Replacement Issues

I replaced my printed circuit board and exciter resistor in the dash today, and unfortunately, they didn't fix my problems.

My alternator still is not charging on start-up, and only kicks in at 1,500 rpm. The left side of the gauges are not illuminated when the lights are turned on. The old printed circuit board was peeling off where the connectors go, so if needed replacing anyway, but, I had the exact same issues before.

To recap, I have a new rebuilt alternator, new printed circuit board, new exciter resistor, and I have cleaned all electrical connections around the car. I have not cleaned the fuse panel, but it "looks" good. Perhaps I need to go there. Any other suggestions are welcome.

Thanks!
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Old 10-25-2008, 11:44 PM
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Tampa 928s
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Did you have the charging problem before you changed you alternator?
You most likely have a ground problem on your lamps, connection perhaps.
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Old 10-25-2008, 11:49 PM
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Tom. M
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Check the exciter wire in the harness that runs across the front of the engine (from the 14pin terminal near the jump post..and runs to the alternator). Mine sagged and rode on top of the A/C belt..chewed into it and broke the wire (as well as abrading others). Ran a bypass wire for now..but will eventually get a new harness up there (or redone harness)

Good Luck
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Old 10-26-2008, 12:13 AM
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Chris Hansen
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I did have the charging problem before changing the alternator. Thanks!
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Old 10-26-2008, 12:24 AM
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WallyP

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Clean and check the 14-pin connector located under the jump start terminal on the right fender.

If that doesn't help, see Tom's post above...
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Old 10-26-2008, 06:07 AM
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Landseer
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Chris, am pretty sure the exciter wire runs into terminal 1 on the 14 pin connector, and then, can be picked up at O8 on the CE panel. You could check continuity with that info.
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Old 10-26-2008, 12:42 PM
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Alan
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From the Exciter resistor it should connect to Z6 then Z1 & then O8 (all should all be the connected together). From there it connects to The alternator D+ (or 61) terminal via pin1 of the engine harness 14 pin connector (as noted above).

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Old 10-26-2008, 04:13 PM
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A quick & dirty check is to see if you have ~11v on the exciter wire, and to see if there is enough current on that wire to light a standard brake light bulb. With a bulb hooked to the alternator end of that wire, key on, engine not running, you should have the charge light on the dash illuminated. Remove the bulb and the charge light should go out.

If the circuit does not behave as described, trace the wires per Alan's terminal designations. With a break in the circuit the charge light will never come on. If it's on even with the wire on the alt side not connected to anything, you have a short to ground on that circuit.
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Old 10-26-2008, 05:21 PM
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Alan
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Actually to Dave's point - does the charge light ever come on? in bulb test? in regular driving? never?

Alan
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Old 10-28-2008, 08:36 PM
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Chris Hansen
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Thanks for everyone's help. I really appreciate it. I had to go out of town for a couple of days, so I'm a little late responding! The alternator light is on after start-up until the engine is revved to 1,500 rpm.

I'll take the pod back off (sigh) and start testing as per the suggestions.

Just curious . . . would it hurt anything to just leave it like this? It charges fine once I'm driving.

Thanks,

Chris
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Old 10-28-2008, 11:08 PM
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Alan
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I'd fix it... if you spend lots of time in slow traffic with cooling fans on - you can run your battery down quite quickly... then you are hosed.

The battery will end up cycling much more than intended and that doesn't help its life expectancy.

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Old 10-28-2008, 11:50 PM
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Chris Hansen
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Thanks, Alan. I've been thinking about this for a couple of days, and am wondering if I received the correct resistor. I think I'll check that as well.

I'm getting pretty fast at taking off the pod! And it will be much less stressful without dealing with the old peeling circuit board!
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Old 10-29-2008, 12:11 AM
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Originally Posted by Chris Hansen View Post
I'm getting pretty fast at taking off the pod! And it will be much less stressful without dealing with the old peeling circuit board!
It's funny how fast you can get at one particular task on a car if you do it a couple times a week.

I'll challenge anyone here to an alternator swap contest, just don't expect mine to work when I'm done!
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Old 10-29-2008, 10:29 AM
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The Bosche alternators in the early cars seem to do this. I have had experience with other alternators that do this as well. It is not that they don't charge below 1500 rpm. It is that they don't start charging until you rev above 1500 rpm or so. Once they begin charging they continue charging until you shut the car off. I needed to rebuild my alternator on my 84 so I took it off. I had my 82 torn apart for other repairs and the alternator was just lying there so I used it for the 84. The pully's were different so they had to be swapped due to them using different width belts. Once I put the Bosche alternator in the 84 it had this issue. It may be due to the pully but they appeared to be of similar diameter. I didn't actually measure them. It charges perfectly. It just doesn't excite until you bump the throttle once.
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Old 10-29-2008, 01:25 PM
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Alan
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Usually that just means the exciter circuit isn't connected at all. Many alternators especially old well used ones have enough residiual magnetism in the rotor that they will generate enough voltage to self initiate at high rpm - once they start up they self sustain with sufficient rpm - all alternators do. The low rpm initial start up is all the exciter circuit is designed for - with a bulb installed it doubles as a charge monitor but thats a secondary thing. If your charge light never comes on and your alternator doesn't start up until you rev it - you don't have an exciter circuit - something is broken...

The only thing that alerts you to this failure is the non-lighting of the bulb in bulb test and the low initial voltage - otherwise the car will think everything is fine - because the exciter circuit will get to 12v as normal - immediately.

Alan
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