134v from Generator

[Alan Homestead]

Hello All, I'm hoping to find a DIY solution here.
My HDKAJ Onan 7500 genset makes 134vac instead of 120vac. In the past year, the output occasionally at start-up was 134vac then within an hour fell to 120vac, but recently, it just stays at 134vac. The repair manual says replace the inverter/controller, which contains the voltage regulator. Since that part is $2000, it would be nice to find the exact cause or internal component, and repair or replace it. Colburn Electronic Controls, Marion, IL will repair the control circuit board -- anybody have experience with these guys? Anyone repaired the inverter/controller themselves?  The inverter/controller is sitting on my workbench now. Much appreciate any trouble shooting advice!!
Alan Homestead, 2004 Beaver Monterey, Bonney Lake WA

[Edward Buker]

Alan,

The folks that repair these type high power inverters probably have pretty unique bench set ups where they can test and diagnose the units. The parts for a lot of electronics today are custom circuit designs that are ordered by the original builder/designer. The days of ordering off the shelf components and building from there has pretty much fallen by the wayside which means our access to parts is very limited.

If some third party is able to fix and warranty the repair then they would be worth a try if it is significantly less cost. Sometimes you can get lucky and a design flaw exists where there is a common repeated failure mode and someone will market the parts for something as a kit but I do not expect that to happen very often or in this case.

 If you cannot find with web searches a good answer to diagnose and repair the unit then your choices are between the vendor you found and buying a new board from Cummins Onan. I have tried to go down this road myself and 98% of the time today it seems to be a dead end...

One last thing comes to mind and that is to order the service manual just to see if in the trouble shooting there might be some high voltage adjustment where a compensation can be made. I think something appears to be shifting and unstable and trying to compensate may not be a lasting repair but possibly worth a try.

Later Ed

[Wayne Tull]

Since it appeared to be intermittent in the beginning.  If it were mine after making sure no electrical charges were remaining on the caps. I would be looking for fractured soldered joints of components mounted on the circuit board. If that's the problem sometimes they can be easy to spot, but not always. 

[Joel Ashley]

I'm with Wayne.  I can't tell you how many times I've gone over a circuit board with my high quality, head-mounted magnifier and found micro-cracks at solder points.  A simple touch with a good 750 degree soldering tip is usually all it takes to remelt the solder, reconnect the tiny circuit, and we're back in business.

On devices that continually heat and cool, the solder and board expand and contract like the wood in your house frame.  Enough of that and miniscule, otherwise undetectable weak points crack where solder connects an electronic component to a circuit board.  Sometimes I can spot them with my bare eyes, but usually it takes at least a hand-held magnifier to spot the cracks that are far finer than hair.

Sorry if the following is getting somewhat away from Alan's request for help, but it may be helpful to others like me who've become disgusted at the unrepairability or the cost of repairing today's electronic devices, and yearn to fix whatever we can ourselves:
My electrician father used an Opti-visor as a magnifier in his day, for all kinds of purposes around house, farm, and workbench.  Having inherited it, we've had it in the bathroom for slivers.  But ever since zeroing in on this cracked solder issue, I grew tired of marching back and forth between bath and shop, so I recently ordered a second one for my workbench. 

They've changed a little since the 1950's, perhaps with a tad lower quality materials and overseas labor now, but still proffer the same basic design and usefulness;  and the lens quality is still up to snuff.  Plus, I added a light kit and jeweler's loupe to the new one, and have to say I'm a very happy camper.  Now if only I could go back 10 years when I didn't have a tremor that confounds my micro-soldering  .  But finally spending on a good quality Hakko solderer last year really helped - the old probe-only Weller and Dremel ones were problematic due to their heating core design.

For those interested, go through the Amazon link off the main BAC webpage and check out the Donegan DA-10 OptiVisor;  and I've found the Euro Tool ELP558 light kit, although not particularly high-end in quality, to be a huge help even over my additional benchtop lights.  There are lots of other options, more and less expensive, but the combination of DA-10, the Ero Tool LED lights, and the Donegan LP-1 Optiloupe have sure made many of my days easier.

-Joel