Zener failed?

My bike is a 72 750, with an original electrical system, apart from a Boyer MicroPower ignition, and LED headlight and rear light.

Earlier this year, I fitted one of those cheap ebay digital voltmeters, just to keep an eye on things. It was reading up to about 15v in normal running with lights - high, but, I thought, probably OK.

A couple of weeks ago, the bike suddenly cut out, and I noticed that the voltmeter was showing low volts. Switched off the ignition while I considered my options. After a couple of minutes I switched the ignition back on, and was surprised to see voltage mid 12's, the bike started without a problem, and as revs increased, the voltage went up, but the ignition warning light did not go out. So my assumption was that the warning light assimilator had failed, momentarily shorting out while so doing. I disconnected the assimilator and have been using the bike since without a problem, but the voltage now reads up to about 16 volts, which is definitely too high.

My assumption now is that the zener was damaged when the assimilator failed (or maybe vice versa).

So I suppose I am now looking at a new rectifier regulator unit. Is there anything else that I should check first? Has anyone experience of the Areg unit sold by AO and Paul Goff? If there are any comments about my assumptions, I would welcome them.

Thanks in advance for any comments.

Have just replaced a Wassell Reg/rect , it was leaking to earth and draining the battery with the ignition off and have seen similar reports so do not buy one of them. AO stands by his product and is a member of the NOC.

Re; “ Paul Goff” both these stand by their products and are quite knowledgeable on electrics on bikes from all over the world. Very rare for a rectifier regulator unit to fail but it can happened. Check earth connection to frame for the Zender is clean, as any paint will obstruct the earth.

I run an ammeter, so I'm not all that familiar with what your voltmeter's high reading means, but it makes sense that it means your zener diode failed since that is supposed to limit the voltage of your system. Why not just replace the zener diode and see if the voltage returns to normal?

i have had no issues with the Wassell units , and i would bet Paul Goff and AO use the same Asia sourced units under thier own branding

i have actually bought Wassell units from Paul goff in the past clearly stamped with the same part number

I believe there are a few test procedures for the Zener. One outlined in the service manual is here:

snowdr said:

So my assumption was that the warning light assimilator had failed,

Click to expand...

If the stock assimulator is to be replaced these might be a worthy option.

https://www.ebay.com.au/sch/improvi...html?ssPageName=&_trksid=p2060353.m2749.l2654

Not sure what solution OP has selected for his issues but I ha 've now had what maybe a similar failure. Bike has been running well with 1.5 year old battery, EI, led headlamp, tail lamp and pilot. Oem zener, alt, rotor, rec. Sparkbright volt indicator seemed ok up to 3500-4000+ rpm then gave the high volt warning. Checked with a digi vom and could see 15-15.8 v at 4k rpm so not good. Kept riding for a few days mainly in town. Went on a long highway ride and had no electrics after fuel stop. Bike did start ok presumably on the 2 MC capacitor charge but would stumble at idle if I put the turn flashers on.
Battery no longer holding charge and shows some bloating on the side panels. Looks like the high volts at sustained periods has cooked it

I've taken zener out of circuit and put a Tympanium reg/rec in place of the lucas rr. Going out to fetch a new battery today. I think I get a prorated discount from this same vendor.

Apologies for not updating the thread.
I discussed the problem with Al Osborne, who was extremely helpful. I sent him my zenor and rectifier for testing, and he confirmed that the zenor was allowing a voltage of over 15.5 volts and climbing, and also that one segement of the rectifier was faulty.
How this all interacted with the original failure of the assimilator is unfortunately unknown.
I have now installed an A-Reg regulator/rectifier, an updated capacitor and a multicolour warning light, all purchased from Al, and everything now appears to be operating correctly. The regulator/rectifier and the new capacitor are mounted neatly on a home made bracket in the space vacated by the old 2MC spring mounted capacitor.