Thank you Max. You've been a great help. And thanks for all the info you posted. I will order the MOC3052 , change it and report back.

Chuck

 

I found MOC3022 opto-isolators in Allelectronics catalog so I ordered some. I also ordered some 5K ohm pots. We'll see if they fix it. Again, thanks to Max, and Joe for the help and info. When I get the parts installed, I'll let you know if it works better.
Chuck

 

Failing that I would do some circuit checking under power as there is the two editions of the schematic posted.
Max.

 

Failing that I would do some circuit checking under power as there is the two editions of the schematic posted.
Max.

Will do Max. Need the pots to be able to connect up the two side by side for comparison.

Chuck

 

I changed the opto-isolator and the pot. still operates the same. Just before pot maxes out, motor stops, SCR Trigger goes out at the same time.. I need to wire up another pot and set up the good MC-60 for side by side comparison. Remember, I only have a multimeter for testing.
I also bought a Sparkfun Arduino Proto board for a DRO project. Got to assemble that next.
Chuck

 

Does the LED in series with the opto also go out? If so it appears the problem is before the opto.
Max.

 

Some have to replace the LED in some recorded instances.
Max.

 

Looking at the schematic posted earlier, the diode you refer to is the SCR Trigger diode. Yes, it goes out when the motor stops.

Chuck

 

I am putting together a more complete schematic of the MC-60, there were a few mistakes and omissions in the original Tim Rollins version.
Max.

 

Great. I think I'll leave well enough alone for now. If I set this controller up to run something, I'll put a physical stop on the pot to prevent turning it to the shut down point. In past research on this controller I found if you put a STSP in the wiper lead of the pot, you can stop and start the motor at the same speed instead of having to rotate the pot to zero speed and back to start the motor again.

Chuck

 

@MaxHeadRoom

Can't wait to see it. That original one does have problems.

 

Time permitting I may investigate the delay start, in the KB DC motor controllers they have two inhibit terminals that can be closed when stopping to reverse, this causes the controller to come up through accel rate when switching from FWD to REV.
Apart from the original T.M. safety concern, the motor cannot start with any kind of immediate command due to the flywheel, which is usually removed when used in a general spindle application which then also aids the previous start position setting..
Max.

 

@MaxHeadRoom

Attached are two MC60 images ... large sized that I found on the net. One was the Robbins and one titled MC-60V8, that looks like the Robbins. I didn't inspect them with great detail, but I grabbed them for clarity.

Do you have any photographs of the MC-60, both foil side and component side? Maybe @chucketn can take some quality high resolution pictures to post.

I noticed the Robbins schematic had the 12V LED's resistor in the low voltage power supply as 5.6k. That is 1.8 mA I wonder if that's true.

Well, I'm heading back to the circuits ...

 

Yes it has been found there are quite a few errors and omissions on Tom Rollins edition.
I don't have any photo's yet, when I finish off the drawing I may add them, together with other observations made by others.
Max.

 

I'm working through the drawing one section at a time. It seems the bridge rectifier has two D4020L diodes and two 1N4005 diodes ... which is the LVPS (12V).

I'm going to continue to use MC60V8 diagram as my reference ... and keep a list of the errors I've think and will hopefully confirm or deny via a board. Each board has a revision on it, from some of the pics I saw on the internet. However, they are not large enough nor has both sides photographed, for me to attempt a trace.

I'll keep you up to date on what I find.

 

From some of my observations so far I have noticed that in many posts and Utube etc, many do not retain or Obtain the motor series choke.
This not only tends to quieten the SCR pulses at low rpm, it protects both motor and drive.
It would be fairly easy to construct if not available.
Max.

 

From some of my observations so far I have noticed that in many posts and Utube etc, many do not retain or Obtain the motor series choke.
This not only tends to quieten the SCR pulses at low rpm, it protects both motor and drive.
It would be fairly easy to construct if not available.
Max.

I have the choke. I have been running a MC-60 on my mill for several
years without the choke with no problem.

Chuck

 

I am not saying it won't run, or even possibly last, but if you have it why not use it?
It is taking chances without it. At least that is my take.
For many years, before PWM took over, SCR drives were used in servo applications and it was customary to see a series choke with these.
Max.

 

There are a lot of the circuits on the internet that work. That doesn't make them well engineered.

 

There are a lot of the circuits on the internet that work. That doesn't make them well engineered.

True, and may well be the case in this instance, but I see no point in removing a device just because does not Appear to make a difference but was included based on established engineering principles, practice and sound reasoning.
If someone comes up with instrumental proof that it has no value in this case, I will recant.
Max.