<div dir="auto"><div>Pete's E-15 is fixed and mowing.</div><div dir="auto"> </div><div dir="auto">I studied the card #1 diagram in the service manual, and looked up the difference between a transistor and an SCR on the net (which was painful - EEs seem to have great difficulty writing for general audiences) and figured it out.</div><div dir="auto"> </div><div dir="auto">The symptoms described in the title - loud clacking of contactors in forward, buzzing relay in reverse - are caused by an open field circuit. This can be from a blown control fuse, corrosion in the fuse block, damaged connectors on the traction motor, or anything else in that circuit, but it's probably going to be corrosion and filth at a connection or contact point, not a melted motor winding.</div><div dir="auto"> </div><div dir="auto">I think what's happening is that the tractor at rest charges a small capacitor, and when you hit the start switches, the capacitor is used to trigger an SCR. If the field circuit is functioning, the power flowing through the SCR keeps it on, a relay closes, and away you go. But if the field circuit is broken, the SCR turns off as soon as the capacitor is discharged... which drops power to the relay, so it opens, and sets the capacitor back to charging, and it quickly charges and triggers the SCR again, so bbzzzzzzzz the relay opens and closes as fast as it mechanically can until you get alarmed by the scary noises and turn it off.</div><div dir="auto"> </div><div dir="auto">This was all new to me because I have a big burly I-5 that beats up cute little E-15s and takes their lunch money. There's no transistors or SCRs in my machine at all.</div><div dir="auto"> </div><div dir="auto">Thank you to everyone who sent advice and ideas, you guys are great, you are what's keeping these old machines alive! Specific particular thanks to Larry Chace who got me thinking about the separately excited field windings and Chad Bushman who set us to checking voltages on the fuse block (yes it was the fuse block).</div><div dir="auto"> </div><div dir="auto">--Charlie <div class="gmail_extra" dir="auto"> <div class="gmail_quote">On May 10, 2017 10:17 AM, "Hank Ralston" <<a href="mailto:Hank@ralstonagency.com">Hank@ralstonagency.com</a>> wrote: <blockquote class="quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> <div lang="EN-US" link="#0563C1" vlink="#954F72" style="margin-bottom:33.75pt"> <div class="m_-4429761017717859881WordSection1"> Hi Chad, Like to know more about modifying the circuit for the upgrade pair of reverse relays. Lots of juice and arching there. The connection do need to be sink wrapped due close proximity to each other. I also modified, gently bent, the contacts to give maximum clearance and still allow for solid connection. Would a diode on one side of one or both relays help? What size and connection would it be? Who might know about it or ideas of where I can search this out? Ordering up the Durrell from Batteries + today. Thanks for comments below, Hank From: bushman165s--- via Elec-trak [mailto:<a href="mailto:elec-trak@cosmos.phy.tufts.edu" target="_blank">elec-trak@cosmos.phy.tufts.edu</a>] Sent: Tuesday, May 09, 2017 8:40 PM To: Charlie <<a href="mailto:medievalist@gmail.com" target="_blank">medievalist@gmail.com</a>>; Elec-Trak <<a href="mailto:elec-trak@cosmos.phy.tufts.edu" target="_blank">elec-trak@cosmos.phy.tufts.edu</a>> Subject: Re: (ET) E-15 clacks in forward, buzzes in reverse, doesn't move.<div class="elided-text"> <div> Lots of small things to consider with this kind of a problem. I would check voltages on the fuse block, specifically top and bottom of each fuse. Make sure the holder is making good contact on both sides with minimal voltage drop. The fuse holders degrade over time and can be problematic for everything. Someone did mention checking all switches in the speed control and I'll second that. The Start switch gets a lot of use and contacts may be burnished. Failing reverse switches can be culprits also. There was a factory update for the reverse relay on the early E-15 models. Don't have the docs in front of me, but i believe it added a diode for one side of the coil. Y ou might check to make sure that has been done. I have a "CA" and pretty sure I added it to mine when I first started working on it due to a similar startup problem. Good Luck, Chad </div> <div> <div id="m_-4429761017717859881LGEmailHeader"> ------ Original message------ From: Charlie Date: Mon, May 8, 2017 5:42 PM To: Elec-Trak; Cc: Subject:(ET) E-15 clacks in forward, buzzes in reverse, doesn't move. </div> <div> <div> <div> <div> <div> Well, we replaced the drive motor's burned stud, but Pete's tractor still doesn't go. </div> When shifted into forward, one of the big contactors clacks loudly over and over, but I can't tell which one of them is making the noise. </div> When shifted into reverse, the open-frame reverse relay behind the dash flips back and forth like a hummingbird's wing, buzzing loudly. </div> Does anybody know what might be the cause of this? The tractor's an E-15 model 26AE15DA. </div> <div> Thanks, </div> --Charlie </div> </div> </div></div> </div> </blockquote></div> </div></div></div>