Home Forums General Discussion Technical Questions Miprom Virgin

I have a Miprom late 80 to 90 that I replaced the 4ea p24107 dual bridge,scr firing board. Car was blowing 4f fuse 10a,that was month ago. Problem back today checked motor had 220k to ground blew out now I got ol. Car will run about 20minutes or so before fuse blows. New board came from Kone spare. Question is what causes this to happen so I can cure replacing boards so often if board is problem.

also the wire diagrams I am looking at are wd-15012 sheet 4of4

i have had this same scenario a few times in the last 20 years, a couple of times, it was just a defective replacement board. I know this because i would go over the usual checks, check the motor field for grounds, check all wiring in the motor field circuit are tight, etc. then just end up replacing the board with a new one, and no further troubles. sometimes when it is intermittent, the board will be tested at the repair shop, and it will test ok. they then wrap it up and send it back out. another thing to maybe replace, is the small aluminum capacitor under the unit, the one that connects to the small choke. i think it is around 4 microfarads, this capacitor can cause troubles, it is cheap, and a great idea to replace on all of the 6010 drives. did you check the motor fields for grounds? you said you had 220k to ground, are you talking about the armature? the armature being grounded will not blow the fuse you are blowing, it will blow the main scr fuses. another tip , maybe not related to the fuse blowing, but will help with erratic problems, is to go through all of the terminals on the drive boards and make sure the are tight. good luck these drives can be a pain, but for their age, they do the job quite well. Did you replace just the motor field power unit, or did you also replace the field regulator board? If it was just the motor field power unit, then you might want to replace or swap the field regulator board with another car

I will order capacitors Monday. the 220k was on the fields but now I read infinity after blowing out. The field regulator board also located on the door? Was also thinking of blowing out tach, thanks for input gator will check wiring also.

Yes the field regulator is on the door, it is 3EA push pull firing board, it sends the pulses to the 4EA SCR board on the top of the door. look on the print, it is the board to the left of the motor field scr board, separated by the dashed lines, it says push pull firing board on it. Keepin the tach clean and brushes good is always a good idea. i have some good info on these drive units if you are in need. pm me your email, and i will send you what i have.