I know everyone gave you good advice. By no means am l an electrical genie. but l will tell you that at one time l had purchased three aftermarket transistors each one was manufactured at different times
The weakest transistor blew out l went to Toyota and bite the bullet and got there new transistors that were a mashed set and never had a problem again.

Hi dear friend
I have a problem with Toyota forklift 6FB30.
When I change direction switch to forward or backward contactors doesnt close to moving forklift.
I check battery
Direction switch
Wiring
Transistor
Please help me
My phone number is
+989395094590
Telegram and WhatsApp messenger I have

I agree that first test should be testing the battery...since in inductive circuits (motors) when voltage drops, amperage goes up. Test under heavy load to see how far the battery drops. If the battery is not the issue, you need to take a hard look at the flyback diode DF1, its associated snubber SN1 for shorts or leak through (a Handyman works great for this). Also it could be the field windings in the motor shorting out. Keep in mind...what kills transistors and other semiconductor components? Heat via high current flow...the load in the drive circuit is the motor, therefore if motor is shorting, you will be pulling high current through the transistors. Same thing for a shorting DF1 flyback diode, it would be bypassing the motor which is the load. Good luck.

Hi a snubber circuit is designed to reduce the high voltages experienced by power transistors when switching inductive loads.

If the snubber circuit fails the the transistor will fail soon afterwards. The high voltage (or back emf) experienced is proportional to the size of the inductive load (L), and the speed at which the transistor switches (di/dt). The formula is e =-Ldi/dt. The - sign represents the fact the the voltage is reversed across the transistor. The physical phenomenon is a property of the inductor (the motor in this case). An electromagnetic field is set up when a current is passed through an inductor, When the current is switched off the inductor tries to maintain this field hence producing the back emf (electromotive force).

By placing a normally reverse biased diode (snubber circuit) across the transistor (collector emitter in the case of a bipolar transistor) the back emf is effectively clamped to 0.7V because once the diode begins to turn on the property of its pn junction creates a depletion field maintaing the voltage across it at 0.7V. If the diode fails due to wear, temperature etc or exceeding it's break-over voltage the transistor is then exposed to the high back emf and will fail.

Most people forget or do not know/understand the function of the diode (normally referred to as a flywheel or freewheel diode) resulting in repeated failure of replacement transistors.

Hope this is clear.

Hi, please explain what is a snubber.

Hi I would start with load testing the batt. Low batt voltage will burn up reistors.

Hello, folks!I have a problem with TCM FB15H15 transistors for drive, for the second time burning up.The forklift after a while driving and stop the display show error A6 and transistors are burnt.


P.S I'm driving forklift with tainted VTM card,whether the card cause to burning transistors.

thanks for the info. now i have a path to take.

repeated SIT problems are usually battery related, if you are certain that the battery is good, remove it and check for cable problems on the cables to the drive motor (melted together or rubbed / smashed.) if none of those are the problem it gets more complex...diodes, snubbers, cpu and dcsd boards. also you need to replace all three at one time. (very pricey) if you have transistor controlled lift you can get creative with some swapping but once overamp'd they're going to fail at some point.