Little Black Box

[sloopjohnrb]

Little Black Box


1962 948cc

Some few months ago, I had a new starter motor fitted.
Ran fine for a few weeks then developed a drop in power.
Red ignition light would come on at the higher revs.

Was told it was voltage, the voltage was adjusted and re-adjusted to no avail.

Informed it was the black control box and was advised to replace it. New control box fitted.

Now, the red light is on constantly.

The control box is supposed to be set at the right voltage level so no adjustment is needed.

Could it be that I have not cleaned the contacts enough-they arrive with a protective coating, or do I need to adjust the voltage at the voltage regulator to fit my car?

All suggestions gratefully received
Best wishes
John

[rayofleamington]

Assuming the box was wired correctly, try re-polarising the dynamo (unlikely but it's quick to do)
To diagnose the black box behaviour you'r best to get a volt meter - they're not so useful on most classic car electronics (I recommend a bulb test circuit) but for the charging behaviour it's almost essential.

[sloopjohnrb]

Hi thank you for your message.
I do not know how to repolarise the dynamo.
I have got a circuit tester though, rather like a screwdriver but with a bulb inside.
Best wishes

[kennatt]

starter motor,drop in power I take it you mean the starter motor has slowed down Due now to the battery not being charged, indicated by the red light being on,is that why the motor was changed in the first place, because it wasn't spinning the engine over.These control boxes rarely fail,more likely to be a fault in the brushes in the dynamo or leads to and from it to the box,or slack fan belt which should always be the first port of call when charging issues arise. If a new box I would be looking at the belt and brushes.

[sloopjohnrb]

Hi thanks for yoir reply.

I meant a drop in engine power and a slight misfire at tick over.
I will check the dynamo, brushes and leads first thing tomorrow.

Best I leave the control box unadjusted, then!!

BGest wishes
john

[autolycus]

A whole boxful of red herrings here, methinks!

At a guess: let's forget the starter motor change, because the engine ran fine for a few weeks after it was fitted.

So now we've got two classes of fault; poor running, and poor charging. There may be a common cause, but I doubt it. I'd tackle the charging fault first, as if you don't, you soon find the battery too flat to start it.

The control box may be OK, it may be OK but adjusted wrongly, or it may be knackered, perhaps by fiddling with the adjustment.

So you need to check the dynamo first. Is the drive belt present, and correctly tensioned? If so, to get any further you'll need a voltmeter (multimeter, DVM). You may be able to get a clue from a circuit tester, but only if you know what it shows when presented with different voltages. The next step would be disconnect the wires from both terminals of the dynamo, tape them up temporarily, then join the two terminals of the dynamo and measure the voltage between them and earth. Start the engine, but do not rev it above a fast tickover.

Stop the engine, and let us know the voltage and how it changes with when the engine speed is increased from a slow to fast tickover. I'd repeat: don't over-rev it, and don't let the voltage rise above 16-17v.

I posted a link to a complete Lucas charging system fault-finding procedure earlier this year, which you may wish to read. And sack the assistant who messed around with the new control box. Was it the same bloke who explained to another poster how his battery voltage could reach 25kV or whatever?


Kevin

[sloopjohnrb]

Hi Kevin
Thanks for the message.

I will be on Gladys tomorrow, and I will follow the steps you outline, getting back to you with findings.
Best wishes
John

[bmcecosse]

Can't add much to the above excellent advice - but the problem is most likely to be the dynamo. Who advised you to fit a new control box?? It's the LAST resort after the dynamo has been confirmed to be ok. Put new brushes in the dynamo - and refit the old control box is my advice......

[beero]

I have got a circuit tester though, rather like a screwdriver but with a bulb inside.

This is no good with 12v car electrics, only limited use with 250v ac house electrics.

[sloopjohnrb]

Thanks for all the advice.
It would make sense for me to get a voltmeter, so I'll get one today.
I will then start on Gladys tomorrow (Saturday), armed with the correct equipment.
Thank you again
John

[bmcecosse]

Get a new set of brushes for the dynamo first!!

[MarkyB]

Both are cheap as chips and a good investment.

[sloopjohnrb]

Problems cured!

Sorry for the delay in the write up, this is due to a slight flooding in the garage problem.

I decided to go right back, and checked the fuses, wiring and the Voltage Reg, which is a new one. All seemed OK.

I then checked battery (which is fairly new) voltage and it came up all OK.

I re-cleaned the terminals on the new Volt reg to make sure any protective coating was off.

I then checked and cleaned all the dynamo terminals prior to testing it as per your guides. I also invested in a decent voltage reader/meter, so was well prepped.

With the ignition circuits on, but engine not started, I was tidying up in the engine bay when I fancy I heard a small electrical arc, or something not connected properly-a zzzz.

I went over things again and at the fuse box I noticed that one of the 3 white wires didn’t look right. I neutralised the battery and decided to have a real close look at the white wires and all those going into the Volt Reg.

One of the 3 whites had a tiny, tiny break, previously, when I had put the circuit tester prong onto the three it must have pressed the white wire into contact and thus showed it was live and working-as soon as I took the prong off it must have stopped working again.

I cleaned and reconnected all wires properly and started Gladys up. The red light went out immediately, and there was no red light coming on at high revs.

Nevertheless I went through all the checks on the dynamo, just to be sure.

I decided to keep the new Volt reg as I didn't want to disturb anything again.



http://mgaguru.com/mgtech/books/pdf/Luc ... _Tests.pdf
Test 1: dynamo gave 2V at 3000rpm, meaning the armature and brush connections are good.

Test 2: dynamo gave rising voltage with rising speed, reaching a full reading (20V) at fast tickover (ca. 1500rpm), settling to 12V around 1200rpm. This is as expected for a good generator. Also, an ammeter was used to link terminals D and F, and the reading was about 2 amps, as expected.

Test 3: Results similar to Test 1, as expected. D lead to control box is good.

Test 4: Results similar to Test 2, as expected. Both cables are good.

Gladys was sounding much better but…still a noticeable rough running on tick over.

I remembered cleaning the jet some time back and wondered if
that might be the problem. I had set the jet EXACTLY the recommended number of flat turns from the top.
I increased the petrol mixture one flat of a turn at a time, simultaneously adjusting down, slightly, the tick over screw.
Eventually I got to the “right” sound, took Gladys for a short trip, increased petrol mixture by one more flat and then did a 3 mile test drive.

Hot starts OK, pulling power uphill as it once was.

I think she’s OK again.
Thank you all, so much for your help, it was invaluable.
Best wishes
John

[bmcecosse]

The real test though is - what battery volts do you get with the engine at decent revs, and then again with the headlights and heater fan switched on - again at decent revs.

[autolycus]

Excellent result - well done!

An easy fault to introduce, then overlook (not saying that's what happened here) is to push a spade (Lucar) connector onto a terminal, but for the male to (Oh God I'm getting into trouble here) go into the wrong hole - that is instead of being gripped tightly (I knew I was) it goes between the female and the sheath (Help!). The sheath holds it on, but it's not making a good connection. Prod it with a probe, and it connects better, briefly. The female, if it's seen plenty of action in the past, can be quite a loose fit on the male even when connected properly, and may need a gentle squeeze with a pair of pliers to tighten things up. A smear of silicone grease can help prevent future problems.

I'd better have a rest.

Kevin

[sloopjohnrb]

Ha ha. Giggle Giggle. I wonder if I should report your post to the moderator?

[Matt Tomkins]

thanks to all for the excelent advice in this thread -- i'd almost given up hope with mine, and stumbled across this thread. exactly the same symptoms! will try methods suggested (checking white cables first!) and feed back

[bmcecosse]

The white cables have no relevance to a charging problem..........

[lambrettalad]

little 50 shades of grey box after that post

[Matt Tomkins]

before i saw this post, i had changed the dynamo for one with new bushes. No luck.
Changed back to the original dynamo.
Cleaned up all the contacts and wires to vr and battery.
still no increase in batter v under revs.

I have changed the battery for the one off my saloon (fed up of the starting handle and a flat battery.

i have now checked the dynamo as directed, and it is working.

I have changed the voltage regulator for the one removed (working) from my saloon when fitting an alternator and new loom.

Still no increase in battery voltage

HELP!!!