Yamaha EF1000is inverter generator - Page 1
Forum section: electronics / repair

author: Renate
author_rank: Super Contributor
timestamp: November 09, 2019, 07:41:05 pm
content: I was fixing a Yamaha EF1000is inverter generator for a friend.That's a 1000W, 50cc generator.This uses a potted main control module that does rectification, chopping and engine throttle control.Initially the electronics were dead, no AC output, no attempt to run the stepper on the throttle.The big electrolytic was bulging and leaking.It's not really replaceable as it is potted with everything else.I Dremeled the cap out and did a post mortem.It had arced and burned internally.I ground it all out and soldered in a new cap.I started the engine and the throttle was going up and down, racing and lugging.At least that was a sign that the microprocessor was alive.I looked at the voltage on the big cap.It was bouncing between 200V and overlimit on my 1000V scale.Yow!I figured that the input 3 phase active rectifier was unhappy or else the control was wacky.Not really much further that I could pursue this.Well, some boiling, some chiseling and some sawing I got down to the input power module.It has 9 diodes and 3 transistors.All the diodes tested good.All the transistors measure the same, that is not shorted on the main terminals.The corner bases (or gates) all measure 73 ohms (in both directions) to the top terminal.This 73 ohms is truly ohmic since I measured with a 2 mA DVM and a 1 mA DVM.I've attached two photos.Does anybody know which module this is? (The paper label on top got stuck to the potting.)Does anybody know what kind of transistor this is? (It couldn't be a good transistor with a built in 75 ohm base resistor, could it?)And finally, everbody wants a truckload of money for the replacement module.My friend is debating buy another generator instead.

author: Renate
author_rank: Super Contributor
timestamp: November 09, 2019, 08:41:23 pm
content: Ok, they are apparently SCRs with an internal ~72 ohm gate resistor.They seem to be OK, at least not shorted.I checked with a power supply and resistor with ~25 mA to raise the voltage to junction voltage.Sigh, maybe the problem was in the control of the SCRs?

author: Renate
author_rank: Super Contributor
timestamp: November 25, 2019, 08:03:07 pm
content: Quote from: Renate on November 09, 2019, 07:41:05 pmLet this be a warning to you.I was using my Velleman DVM, inexpensive, but not total junk.I had had it a few years, always reliable.The old module had arced and burned inside, at least I'm sure/grateful for that.The new module went in, worked fine.I went to check the AC voltage output and my meter was going wacky.With the probes shorted together and one foot from the engine it went bonkers.I had never seen any meter so sensitive to the ignition EMF.I checked the insides, the typical aluminum tape with a grounding spring to the PCB.Years ago, a friend of mine built a circuit that accidentally triggered when someone ran a vacuum cleaner in the room.I built a replacement circuit and to prove/test it, I demonstrated it operating with a 15 kV neon transformer arcing to the inside of the case.I guess that I should bite the bullet and buy a Fluke.