GML Enterprises

[Peavine]

I read on another forum that Gene Lewis of GML has passed away, and GML is no more. I learned this today because coincidentally one of my walkaround throttles Started acting up, and I was going to call Gene to see if he could help me troubleshoot it.
 It seems to me that some component inside of the unit failed.

 Symptoms are:

 The DC output polarity is reversed from what it was.
 The unit is only sending about half power out to the track.
The memory function is not working. In other words when you unplug the handset to walk to another port, the trains stop.

 I know that a bunch of you guys on here are a lot smarter with electronics than I am. my brother, who is an electrical engineer, suggested that if I can get a copy of the schematics we can work our way through it and fix it, but I’m not sure I feel comfortable calling Marion (Gene’s  widow) and asking if she has a copy of the schematics of the controller. Anybody have any suggestions on what I should do or what components might need to be replaced in this unit to make it work again? I’ve had the unit for less than three years but I love it and would really like to get it working again. It’s not as simple as just getting another brand of walk around throttle, it’s a rather large layout with three sets of throttles

Thanks for suggestions guys,
Jim

[Peavine]

Oh, I forgot one last symptom, with the controller at zero (train stopped), there is still 1.85 volts going to the track. If you turn the controller all the way up, the unit is sending 10.03 volts to the track. If you reverse, then there is only 8.18 volts getting to the track (a difference of 1.86 voltsj. At wide open throttle, these units will send 21 volts to the track, so there is only about half voltage being produced. Yes, there is a volt-meter in the system, no, I don’t generally run trains on more than 12-14 volts.

Thanks for any ideas you guys have.

Jim

[NtheBasement]

I have a GML but haven't used DC is a while.  It's probably 30 years old.  With delay set to zero, pulse mode to off and no load I measure 0, +20, and -20 vdc.

One of your symptoms - half speed - reminded me of something.  IIRC there is a way to set it to half speed by hooking the transformer using the center tap instead of one of the normal terminals, which supplies half the voltage.  There is also a mod (I sent it back to GML) to get the throttle to run everything half speed.

My WAG is the problem is something like a diode in the throttle but still worth sanity checking.  I would start by unhooking the xformer and checking to see if it is still 16vac.  Then I would check the connections to the control unit and to each of your throttle sockets.  Also would suggest unhooking the controls from your track, removing your locos, checking rail-to-rail resistance for partial shorts, and rail-to-rail voltage indicating crossed connections to lighting etc.

Of worst comes to worst there is an entire GML system on eBay or $50, ends in a few hours with no bids.  https://www.ebay.com/itm/265128902001?hash=item3dbae9fd71:g:AfMAAOSwkUZgcKsK

[mmagliaro]

This is really sad.  And I took a look at the archived pages of GML in the wayback machine to see if he every posted full schematics of his designs like some other throttle makers do.  Unfortunately, he did not.

The transformer and diode checks are good ideas, but unless there is some obvious burned component inside, I would have to draw out a schematic from the unit.

EDIT- I noted the other post about there being two of these for sale on eBay, and that ad includes some photos of  the inside.
Like most "transistor" throttles, there is not really a lot in there that can fail, especially not like this.  You've got your basic diodes, a few transistors, electrolytic caps,  what looks like a regulator (but the photo is fuzzy)...   One of those big electrolytics shorting out might cause this depending on how the circuit schematic is designed.

Any chance you can take some CLOSE, SHARP photos of the insides to post here?  Maybe one of us will see something.

I would try measuring voltage across the transformer, and across each of those electrolytic caps.

[C855B]

I've seen similar symptoms in similar products. The polarity reversal and half-power issues point to a bridge rectifier with a bad diode. That the memory function doesn't work would be a downstream effect of the polarity reversal. If it was on my bench, first "tool" I'd point at it would be an oscilloscope, to verify what is likely to be half-wave output.

The bridge rectifier is clearly shown in the next-to-last photo on that eBay listing. It's that four-diode cluster at the back of the top board.

[peteski]

I've seen similar symptoms in similar products. The polarity reversal and half-power issues point to a bridge rectifier with a bad diode. That the memory function doesn't work would be a downstream effect of the polarity reversal. If it was on my bench, first "tool" I'd point at it would be an oscilloscope, to verify what is likely to be half-wave output.

The bridge rectifier is clearly shown in the next-to-last photo on that eBay listing. It's that four-diode cluster at the back of the top board.

The problem is that Peavine likely does not have an oscilloscope handy.  For all we know, he might not even have a multimeter.

[C855B]

Oh, I know that. I'm just saying that's what I'd do. Multimeters with diode check functions are a dime a dozen, tho'. All MRRs need one in the toolbox.

[peteski]

Multimeters with diode check functions are a dime a dozen, tho'. All MRRs need one in the toolbox.

Absolutely.  Every model railroader needs to own a multimeter.  They can often be had for under $10 (plus shipping).

[wazzou]

I got one for free just walking into Harbor Freight with a coupon some years back.

[Peavine]

Wow,
I knew I could count on you guys for a solution!
First, thank you to Nthebasement. I solved the immediate problem with the purchase of the ebay stuff. Now I can at least keep the trains running. Here are some photos for your enjoyment (I still want to fix this thing if I can. It will be an interesting project, and I might learn something)

[Peavine]

And some more:

[Peavine]

Oh, and I do have a multimeter, just not an oscilloscope

[mmagliaro]

Let the remote diagnostic guessing begin!
Note the white circled areas in your photo below.  I can't quite see close enough, but those solder joints
on the pins from the bridge rectifier, and also on that regulator (also circled) look pretty bad.  Can you check those
and see if  the pins are actually loose in the holes?  You could resolder those to see if it helps.

And since you've got that meter... measure what voltage you get across the "+" and "-" terminals from that bridge rectifier.
I noted a "+" on there because I think I see a "+" mark on the board on that end pin from the bridge.
I would guess the "-" is on the opposite end (i.e. if the "+" is pin 1, then all the way over at pin 4 is the "-")

[jagged ben]

Oh, and I do have a multimeter, just not an oscilloscope

Then you are a normal man.   

[Peavine]

Yes, there is a minus on pin 4. I touched a soldering iron to each blob to make sure the solder joint was good. I checked the voltage across pins 1-4. With volts AC, I get 182.5.. if I put the multimeter on DC I get 82. I don’t have a clue what that means, but there it is.