[fragger6662000]

I have a chester conquest of the 2005 era.

it seams to have a KBIC control board.

The problem that the machine has little speed and even less torque, the spindle can be stopped with my hand. Any ideas, i have tested the power resistors and they seam to be OK.

And ideas?

[Al_The_Man]

It sounds like you may have an open side on the control bridge components, there is two SCR's and two diodes in the bridge.
Did this just happen?
Al.

[fragger6662000]

yes it did just happen.

i was parting off and the tool snatched and stopped the head causing the head to stall and break a couple of teeth in the headstock. The motor was stall for about 5 -10 seconds.

after replacing the gears and changing to taper roller bearings. I thought i might as well when the machine is in bits i put it all back together to find the current situation.

matt

[fragger6662000]

now just slow speed even if the pot on the control is in the off position.

[LeeWay]

I have had a pot go bad. They have the switch inside as well as the pot. Just cheaply made. I had to order a couple replacements from little machine shop.

[Al_The_Man]

yes it did just happen.

i was parting off and the tool snatched and stopped the head causing the head to stall and break a couple of teeth in the headstock. The motor was stall for about 5 -10 seconds.

The fact it happened due to a stalled motor indicates the power side may have been damaged, Once you have it corrected, you may want to make sure you have the correct limit resistor in place and the current limit pot is set correctly.
The limit resistor is sized according to motor HP.
Al.

[fragger6662000]

the speed control pot is ok, as i have just checked it.

[fragger6662000]

Right i have track down the problem to the SCR as you stated in the first post.

the only problem that i have now is that i cannot find an equivalent part and cannot find a data sheet for the current part. Does anyone know a different part that can replace A69108.

thanks matt

[Al_The_Man]

They are not really that critical, in fact I repaired a Bridgeport by fitting larger components off board on a heat sink.
Look for 300~400v 10 to 20 amp SCR's, you may have to do a little reverse engineering to come up with the pin out polarity, but they are generally standard pin out.
There is 2 SCR's and 3 diodes. The diodes are fitted with 3 leads also.
Al.

[fragger6662000]

i found the data sheet for the diode and they are fine. i have never had so much trouble finding information on a single component as this one. thanks for the information.

matt

[Al_The_Man]

I forgot to mention they are Teccor components, I think they are now owned by Littlefuse.
Al.

[CarveJunky]

This is a long shot but if the electronics check out you may want to check the pre-load on those bearings. I am just mentioning this because I had rebuilt a lathe headstock and had similar results. I decided to check the mechanical side first and loosened the bearing pre-load. Ooops, saw the SCR post after...

Carvejunky

[fragger6662000]

the pre load on the bearings is ok. they just need a little running in as the grease needs to be moved about.

[fragger6662000]

right.
according to the KB people the current direct replacement is S8015L or S8020L and at £2.50 each it was not too bad.

thanks for the help.

[Al_The_Man]

Handy to know, thanks.
Al.

[fragger6662000]

well the progress now is the DC motor and board is dead.

i have purchased 3 phase inverter and motor and in the process of hooking it up to the machine with different toothed belt and pulleys.

i tried v belts and found that they slipped too much.