Sw 1200 switcher

Sw 1200 switcher

Postby jmass » Mon Feb 18, 2019 8:32 am

Just received my Lok @ rol sw1200 switcher. Ran it for ten minutes in both directions and it ran fantastic. Next day it ran great for a while and then stopped running in the forward direction. Also no directional light. However it runs fine in reverse with light. Before I take the board off are their any suggestions what I should be looking for? My PVM f3 also runs fine in both directions so I am scratching my head on this one.
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Re: Sw 1200 switcher

Postby AstroGoat760 » Mon Feb 18, 2019 9:25 am

That is a bit of a head-scratcher. It does sound like something is up with the circuit card, if the loco only runs in one direction. I would check to make sure that the jumper plug for the DCC slot is in snugly, and that the solder connections look good.

Could you send pictures of the loco when it is opened up, and I might be able to help troubleshoot it?
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Re: Sw 1200 switcher

Postby RodTT » Mon Feb 18, 2019 12:07 pm

The first SW1200 I bought ran ok but the front light wouldn't come on. I took the shell off, just bent the wires holding the front LED upwards slightly, and all was well. Could be something as simple as that.
Also, the other day my other SW1200 stopped running at all - at a show as well. I just worked the gears in the trucks to and fro a little with a screwdriver and it started again.
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Sw 1200 switcher

Postby CFRiad » Mon Feb 18, 2019 1:37 pm

AstroGoat put you on the right track.

Before you start the diagnosis, remember that the loco runs with the body shell off, so testing is quite easy.

If the lights don't work correctly start the diagnosis with checking the DC jumper chip. Remove it, clean the pins with an electronic parts cleaner, reinsert and test.

If the problem persists, remove the circuit board screws, unsolder the four track power collector wires and note the board orientation so that you know how to put it back later. Lift the board. It has two contact blades underneath that feed the power to the motor. Look for two contacts on the motor body. Use two probes to feed 6-10 V of DC power directly to the motor. The motor should run. Switch the probes around to run the motor in the other direction. If the motor runs in both directions, clean the contact blades on the board and the contacts on the motor body. Reinstall the board, ensuring it makes good contact with the motor body. Re-solder the track power wires to the board. Test again.

If the motor doesn't run when you feed power directly to it, the problem could be mechanical or with the brushes. Try turning the motor axle by hand. If it turns smoothly, the problem is likely with the brushes. I don't know how to remove the motor and fix the brushes. If the axle doesn't turn smoothly, clean the gear train and lubricate very lightly.
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Re: Sw 1200 switcher

Postby jmass » Thu Feb 21, 2019 8:21 pm

Well it seem I learned a very important lesson here. Check the output voltage of your power pack before you run a loco. The switcher is rated for 12 volts maximum and the power pack I have is from an Atlas trainman set and puts out a maximum 17 volts peak. So warranty voided I will have to find someone in Jersey who does repairs.
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Re: Sw 1200 switcher

Postby krokodil » Fri Feb 22, 2019 4:07 am

You did not mentioned the electronic system: Is it analog or digital. In digital I would say that the decoder electronics failed (one or two transistors in the H bridge - power output).
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Re: Sw 1200 switcher

Postby jmass » Fri Feb 22, 2019 8:09 am

It was straight out of the box analog.
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Re: Sw 1200 switcher

Postby krokodil » Fri Feb 22, 2019 9:51 am

jmass wrote:It was straight out of the box analog.



Than follow CFRiad instructions. It should be a big issue. The analog throttle very often gives more than 12 V out, it is very normal and I do not think that this can be a problem for the warranty.
I assume ( if you already know that the throttle delivers 17 V) you have some instrument ( the cheapest one is enough). Try to find out if there is voltage on the motor in FWD. I will expect there nothing,or just 2-4 Vs. That means you have some short in one direction. The LEDs, diodes and the wires to the LEDs can short the motor.
If you disconnect all those thing and keep just the motor in circuit you will see what is the reaction. From here I would say that one of the SMD diode is broken. Easy to detect with almost any DVM.
Good luck.
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Re: Sw 1200 switcher

Postby CFRiad » Sat Feb 23, 2019 1:44 pm

Aaah, the power of multiple brains...

krokodil is right. I limited myself to finding bad contacts and didn't consider a failed electronic component.

krokodil wrote:Try to find out if there is voltage on the motor in FWD. I will expect there nothing,or just 2-4 Vs. That means you have some short in one direction. The LEDs, diodes and the wires to the LEDs can short the motor.

If the motor turns in both directions when you feed power to it directly but doesn't with the board on, the problem can be a component on the board. To test what krokodil is suggesting, with the board still off, make sure the DC jumper chip is inserted correctly. Solder two temporary wires to the board input where the track power pickup wires are normally soldered and feed 6-10 V to these. With a voltmeter, measure the output voltage on the two contact blades under the board. Switch the input power feed polarity. The board input and output voltages should be equal to each other in both cases. It they are not...
krokodil wrote:I would say that one of the SMD diode is broken.

In this case, the first thing I'd try is to replace the DC jumper chip with one from another SW1200 that runs. Repeat the measurements above. If this results in correct voltages, the problem is with one of the diodes on the chip. I am sure somebody on this forum has a spare DC chip.

Therefore, I would like to correct
krokodil wrote:It should not be a big issue.
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Re: Sw 1200 switcher

Postby krokodil » Sat Feb 23, 2019 2:02 pm

Thank you for correction, I wanted to write this - the "not" dissapeared during editing.

If there is not a spare DC plug, it is still relatively easy to repair, just one diode should be replaced. In worst case - it the loco remains in analog mode one 1N4002 will fit also.
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