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Re: (ET) E15, troubleshooting field weakening
Graham Allan wrote:
The FW relay is fine - speeds 4-7 operate as normal if the relay is
If I measure voltage across the relay (wires 13 and 39, or contacts 12
and 15 on the card), I see 0.7 volts. Odd number... looks a bit like a
diode voltage drop?
Probably across CR108 (and the IR drop across R220.
To complete the testing, I can get all speeds if I jumper between card
contacts 14 and 15, which closes the FW relay using the 2A contactor
output. Doesn't seem like this can do any harm, other than losing the
time delay between 2A and FW.... but it's obviously no real fix.
looking at the schematic, I think the main value (to me) of the 4 relay
drivers is to avoid arcing on the micro-switches when the driven relay
turns off. But, on at least the E-20 DA and EA, as well as the E-12
drive, the relays are driven directly from the micro-switches, so
jumpering 14-15 shouldn't hurt especially as the current draw on the
open frame relays is less than the big contactors.
When the SCR turns off it blocks the reverse voltage spike from the
relay coil and the diode/resister pair takes the energy.
Another other use of the drivers may be to avoid dropping the relay out
if the circuit is opened momentarily, say on a bump.
The driver may be there to cause a delay before relay actuation for some
reason.
So there are only about 7 components on card 1 which could be
resonsible for this failure, but I'm not sure where to look next! Has
anyone encountered or fixed this before?
SCR 105 caries the load, and Q103 ( the silver can ) drives it. Next,
C105 is 1 uF / 100 Volt in a small package for the time, pushing the
dielectric. If shorted it could keep Q103 from firing. You can measure
the resistors directly.
The card is a pretty recent Bill Gunn model, by the way. My original
card basically didn't work (a few components looked as if they had
either vaporised or otherwise disappeared, and another spare worked but
also lacked field weakening - maybe the same fault). I really feel I
should be able to repair this one...
From the list, the most common failure of this card seems to be the
edge connector, but shouldn't be the problem in your case. On my E-15
the transister can corroded off so I jumpered like you did.
--
Paul Abendroth pabendroth at dma dot org
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