EZGO TXT - Controller - Undervoltage issue?

[Cartman Z]

hi guys - i am trying to diagnose a no-go issue, have replaced half the cart at this point, and still at a dead-end. tried to provide as much detail as possible below - any help or advice would be great! thanks

2005 ezgo txt 36v shuttle.
cart is no-go.
solenoid no click.
resistor burning hot with cart off (even without neg terminal of batt pack connected).
old f&r switch was burning up, wires getting very hot and melting into switch.
i upgraded to heavy duty f&r which held for awhile but that eventually melted too.
batteries were way old, and not holding charge.
i installed new batteries.
my wife drove it for two miles, smelled electrical burning (which was a familiar smell from wires melting into f&r switch). she made it home, but then heard a "pop" from the battery compartment and the cart died.
i then installed all new cables, and new heavy-duty f&r switch.
fyi, i upgraded cables from 6-gauge to 4-gauge, including the runs from the f&r switch to motor, etc.
ran it around the block a few times. worked great! more torque and speed, cables cool to touch, f&r switch not melting.
backed it down driveway to park it and, without any noises/etc, it just died. no fwd or reverse.
with f&r switch in reverse, i got the beeping but only intermittently.
pushed it into the garage.
upon closer inspection, resistor between large poles on solenoid was burning hot.
troubleshooting online indicated solenoid may be bad.
i replaced solenoid, but no change. still no go, resistor still burning hot when batteries connected.
thought it could be reed switch, but that is already bypassed.
no signs of chaffing or breaks in any wiring.
pulled up floor mat (using knife and beer), opened the control box for accelerator. all wiring good, connected properly, micro-switch opening/closing as it should.
next step...gulp...speed controller?!
(alltrax 400amp ITS, series)
connect batteries, turn on key, depress accelerator, led blinks 6 times. alltrax online info states it's an undervoltage alarm.
checked batteries - holding a 38v charge.
alltrax says check voltage between B+ to B- on controller. should be within ~5v of pack voltage.
ah-ha! it reads only 12.7v.
however....alltrax says this indicates bad solenoid...which is brand new.

so i've come full circle and don't know what to do other than replace the controller - not sure if there's anything else i can test/check/etc. would love any advice you guys might have! thanks in advance!

[JohnnieB]

The pre-charge resistor is hot and the voltage at the controller's B+ is low, so excessive current is being drawn by either the filter capacitors or the MOSFETs inside the controller. Don't know which, but in either case, the controller is bad.

Replace it with an Alltrax SR48400 (or larger) controller, which is two generations newer than the AXE (or NPX) that is installed.

[Cartman Z]

Thanks JohnnieB! I was afraid of that, but it's great to have the 2nd opinion of someone who clearly knows what they're talking about! And thanks for the recommendation on the type of controller to go with. Will let you know how it all goes...

[Cartman Z]

Update:
I ordered new controller as spec'd. It came with a new solenoid, diode and resistor. Installed all three, still no go.
Resistor is larger than the previous one so doesn't get hot as quick, but still gets hot.
4 Flashing green lights on controller indicated bad ITS.
Replaced ITS and microswitch.
Still no go.
Flashing light indicator on controller (1 green, 6 red) now states it's a precharge failure.
Alltrax troubleshooting guide in the manual says precharge failure indicates a "stuck" solenoid.
Performed continuity test between the two small terminals of the solenoid, and it failed test.
Electrician friend and golf cart shop both agree solenoid needs replaced.
New heavy-duty solenoid is on order.
Anything I'm missing here? Steps I should check in the meantime while waiting for part?
Thanks!

[scottyb]

Solenoid test attached. Recheck.
If the solenoid is not being activated when the controller is powered up you will get the precharge error. Solenoid activation occurs when there + and - at measured between the 2 small terminals