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MG MGA - RB 106 boxes

I raised this query on the Sprite/midget list, but didn't really get any resolution, so I thought I'd try here.

I'm just completing my third car. This is a 1959 Sprite (the others (which I still have) are a 1966 Sprite III and a 1959 MGA 1500). All these cars have RB 106 regulator/cut-out boxes. All of them also have in common the fact that they came to me after sitting idle since the 1970's, in circumstances suggesting they had failed their annual MoT and had been abandoned (in one case in long grass). The 1959 Sprite, now that I have the engine started after the rebuild, refused to charge, just as the first two did, despite points cleaning on the regulator/cut-out boxes, and I have to get it charging, as before, by the simple measure of buying another one of these repro (Chinese?) boxes. With one of these fitted, it charges fine. At least they are cheap.

I rather resent having to replace an original bit of the car if I could repair it, but I can't work out what can have gone wrong with a bit of kit which was probably working fine when the car was laid up, apart from the points, and I've cleaned those. It looks like a fairly simple bit of electro-mechanical kit and it annoys me that I can't fix it. Does anybody have any idea what goes wrong with them? Is there, perhaps, some permanent magnet that deteriorates?
Gus Gander

I don't know if it's the same as a motor cycle charging system, but after along time laying up I some times have to flash the field winding of the dynamo to re polarise it.
This is something I havent done for a long time so I will have a look in my old books
Ian Mc
Ian McGregor

All the dynamos were in good order. And I'd polarised the frogeye's dynamo just before starting up, as I wasn't too sure it belonged on the car. No the trouble is definititely with the box.
Gus Gander

There are several good on-line troubleshooting guides if you do a search. I can't seem to remember them right now. But my first suggestion is to clean the contact points with a bit of emery paper. The contact could have become tarnished and not work.

These are pretty basic electro-mechanical devices, but the way they work in the system, is not so straight-forward to many.

Chuck
Chuck Schaefer

Gus - I don't know what the shipping charges would be, but there is a gentleman in the US that will make up a solid state regulator, install it in your original box and calibrate it to your generator type. The cost is $80 USD plus shipping. His name is Bob Jeffers and his e-mail address is: bobj20@adelphia.net Cheers - Dave
David DuBois

I think it's the fine coil under the tape on the regulator side, but haven't taken one apart to find out. Are there any old rebuilders out there that remember the most common failure?

It would seem someone could fix them for less than the cost of a new one. If the points weren't beyond cleaning.
Tom

From what I think I remember reading, it seems as if you'll have to re-polarize them after sitting for so long, since the magnetic fields will have dissapated over time...?? I can't find the reference for this just now, but IIRC it was in the answer to a letter posted to one of the tech sites like MGA Guru.
AJ Mail

To polarize a generator just touch a hot jumper wire momentarily to the field terminal. That's it, regardless of vehicle system polarity.
Barney Gaylord

When I purchased my latest MGA I noted that the flat metal permanent wiring underneath the control box had burnt out and melted. It was either A or A1, and the previous owner had simply joined the Brown and Brown/blue wires of these 2 contacts together on the terminal that wasn't melted underneath the box. I think there is a possible cause for this occurence, which is, when investigating and pushing in the cut-out contact it will stay in and the contacts weld together as it is virtually a dead short which if left in will melt the bar underneath. So beware and ensure that you can remove a battery connection quickly if this happens. I ended up soldering a small flat strip across the "melt" and fixed the problem - charging was and still is fine. Hope this helps.
Tony Clarke

This thread was discussed between 25/10/2006 and 27/10/2006

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