Monarch square dial 1/2 speed

Flightmap · May 19, 2018

My 1963 10ee was working fine until the other day. I warmed it up and then engaged the spindle lever prepatory to turning the speed control. The machine powered up to 4000 rpm immediately. Since I almost always power the machine down with the speed control set to zero, this surprised me. I immediately backed the speed down to zero.

i ran the lathe for about three hours and couldn’t get it to run faster than 1200 RPM (indicated), but it responded to settings below this number. Remembering that the pot was dual stacked, I figured it was OK to run that day.

i checked with a member here and he suggested I look at the diodes on my machine for the lack of upper end speed.

My question: does anyone have a list of diode conversion numbers/mfg’s for all the diodes?

according to another post here, there is a issue with the brackets for alternate diodes. What is the work-around for this?

if you have dealt with this problem, would you suggest I just ask Monarch for a complete array of diodes and replace, Or, look into alternative diodes and brackets? $$$ not with standing

thanks in advance, Ken

John S01 · May 19, 2018

On the inside of your module box cover should be a map of the diodes, here is a picture of mine
Shared album - Module Map

This shows the polarity of the diodes, they are flipped around at random. There is no issue with the brackets, they have polarity and the diodes must be installed in the correct orientation. The brackets that hold the diodes have guides that may not be easy to see, but pull a diode out and flip it and put it back in and you will see how the diode no longer fits in it's bracket.

Shared album - Module Box

The Monarch diodes are old school electronics and there are better versions available today for cheap, but you will either need to machine end pieces to fit the brackets, or just solder the diodes directly to the brackets.

I forget what the rating of the recommended replacement diode is, maybe 1 or 2 amps, very common parts, search the archives.

There is also a photo of a module that has lived a hard life. It has a few soldered diodes. Note the burn marks on the diagram that correspond to the replaced diodes.

While you have the module out, check (and record) the resistance between the terminals of the potentiometers.
You can also loosen them and check the resistance of the terminals over the range of the pot.

It is always a good idea to swap with a good C3J replacement tube when troubleshooting a modular.

And you can always buy a refurbished module box from Monarch, they are only $2000.

rke[pler · May 19, 2018

If you poke around in this forum you'll find several posts where folks made the mounts for inexpensive replacement diodes from brass. The replacements are cheap and you can turn the brass with the speed you have remaining. Here's one such thread that suggests using 1N4004 diodes as replacement:

http://www.practicalmachinist.com/vb/monarch-lathes/diode-replacement-98808/

Alternatively you could buy a functional replacement for the module here:

For Monarch 1ee Lathe

reidry · May 19, 2018

John S01 said:
On the inside of your module box cover should be a map of the diodes, here is a picture of mine
Shared album - Module Map

This shows the polarity of the diodes, they are flipped around at random. There is no issue with the brackets, they have polarity and the diodes must be installed in the correct orientation. The brackets that hold the diodes have guides that may not be easy to see, but pull a diode out and flip it and put it back in and you will see how the diode no longer fits in it's bracket.

Shared album - Module Box

The Monarch diodes are old school electronics and there are better versions available today for cheap, but you will either need to machine end pieces to fit the brackets, or just solder the diodes directly to the brackets.

I forget what the rating of the recommended replacement diode is, maybe 1 or 2 amps, very common parts, search the archives.

Here is a photo of a module that has lived a hard life. It has a few soldered resistors. Note the burn marks on the diagram that correspond to the replaced diodes.
Shared album - Module Box 2

While you have the module out, check (and record) the resistance between the terminals of the potentiometers.
You can also loosen them and check the resistance of the terminals over the range of the pot.

It is always a good idea to swap with a good C3J replacement tube when troubleshooting a modular.

And you can always buy a refurbished module box from Monarch, they are only $2000.

I also think your module is probably repairable.

If you end up needing to replace the module, one of the forum members recently designed and is selling a replacement for the module.

For Monarch 1ee Lathe

Ryan

hitandmiss · May 19, 2018

I have made replacement diode assemblies for several machines.

I used 1N5408 3A 800 PIV diodes. The package has a larger dia. lead and a longer package than a 1N4004

Lots available on ebay for less than 20 cents each for 10 to 20 Pcs. and free shipping.

There were a couple of threads in this forum covering the construction of these.

Cal Haines · May 19, 2018

OK. But I think OP's real question is whether or not his speed control problem is due to a diode issue or something else. Anyone?

Cal

adh2000 · May 19, 2018

Cal Haines said:
OK. But I think OP's real question is whether or not his speed control problem is due to a diode issue or something else. Anyone?

Cal

Yeah, I've had the same problem twice. Once it was because oil had fouled the speed control pot. The second time was because the C3J tube had burned out. Why do you think this is a diode problem?

Flightmap · May 20, 2018

Yes, adh2000. I don’t know that it is a diode problem, but from the posts I read, it seemed logical. As stated, i know nothing of electricity, so I read what others say and try to draw my own conclusions (not the best, but it is a start)

i Looked in the other compartment at the three tubes, and couldn’t see any visible problem with any of the tubes. Based on several comments on polarity, and potential shorts, I didn’t test them.

regarding the speed control pot: I’ll Take the back cover off (need to do this for another problem anyway) and see if I have any excess oil around the speed potentiometer. Don’t remember seeing the back of the pot in the cavity, but will look again.

to all above, thanks for taking the time to read and comment. Aside from Monarch’s ability to replace the “black box” is there a recommendation for someone who has designed a replacement for the box or diode rack (either or both) that is a simple install? The site titled SSE(?} (I think this was Ryan’s suggestion) mentioned above may be more than I can handle. I’ll ask them Monday, but it may be beyond my ability or comfort range.

again, my thanks for all the responses
Ken

Colt45 · May 20, 2018

The speed control pot should be inside a cast iron housing just below the right side main spindle belt tensioner.

The module pretty much plugs in and out, there is a thumbscrew that holds it in. You can remove your module, clip a few wires and ship to Scissio and they will do minor surgery on it for you. Then you just plug the new one in. Read the pdf at Scissio site for instructions.

Spindle module replacement complete

Flightmap · May 21, 2018

This is what I was looking for regarding the diode replacement issue and didn’t realize when I read Ryan’s post, what they were talking about.

Now that I have a potential solution, I’ll focus on the other possible causes of my problems. Thanks to you all for you time and thoughts

hitandmiss · May 21, 2018

Start by pulling the module,power up and start spindle.
The spindle will run but not have any speed adjustment, at about 2000 RPM.

Let us know what you have found.

Bill

Cal Haines · May 21, 2018

adh2000 said:
Cal Haines said:

OK. But I think OP's real question is whether or not his speed control problem is due to a diode issue or something else. Anyone?

Cal

Click to expand...

Yeah, I've had the same problem twice. Once it was because oil had fouled the speed control pot. The second time was because the C3J tube had burned out. Why do you think this is a diode problem?

I have no idea if it's a diode problem or not, hence the question. I don't know much about 10EE tube drives, but I recall that modular-drive machines have problems with diodes. OP contacted me off-line, so I sent him here for a solution.

Cal

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