# Transformer testing question



## krewzn_along

I just brought out my childhood HO train set (from the late 60's or 70's) along with some more HO track and engines & train cars from my wife's family. 

I'm troubleshooting to find out why the engines are not working. What should I see on the output of the transformer? It is a TYCO--Model No. 899T Hobby Transformer. I'm expecting it is from 0 to 19v DC, varying over that range with the speed control on the transformer.

What I'm getting is 0 or 19-20V, nothing in between. And I am getting that at the loaded or unloaded terminals of the transformer and on the tracks.

Should it vary the voltage or the current at a constant voltage to control the engine speed?

Thanks - My Christmas train is waiting for your comments!


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## waltr

Without a load (engine) on the variable output you'll see about 19V (I have a couple of these Tyco transformers).
You can get a variable voltage with a load. Try about a 100 Ohm, 10 Watt resistor across the output.
Or try connecting the TYCO 899 to an engine.


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## rrswede

Included with a recent purchase of a box of used transformers were several low end Tyco type 899 transformers/powerpaks. All were bench tested for performance. All provided fixed AC voltage of about 20 VAC. Some provided variable DC voltage between 0 - 18VDC and others, as in the case of the original post, provided only no voltage or fixed voltage of about 18VDC, regardless of the position of the sweep arm.

Although I did not apply a load to any of the transformers while testing for voltage performance, as suggested in the single response, I question the accuracy of that response and would appreciate further input. 

The fact that some units performed as expected and others did not leads me to believe that some internal component has failed.

Thank you for responding

swede


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## Cycleops

I shouldn’t bother guys looks like krewzn along has krewzed on out!


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## CTValleyRR

Rrswede, you did dredge up a really old thread here.

Me personally, i wouldn't waste any time on an old Tyco power pack. They were never that good to begin with.

I would advise anyone reentering the hobby to spring for a new powerpack, or consider switching to DCC (although many of your old locos may not be suitable for conversion).


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## rrswede

CTValley, thanks for responding.

Yes, I did dredge up an old post, yes the Tyco's and other similar devices were close to junk and yes, anyone entering or re-entering the HO hobby would be better served with a new power pack. 

However, as a O gauge tinkerer unfamiliar with these power packs, but wanting to learn what component typically failed in them to cause DC voltage to become fixed rather than be variable, I searched this forum. 

When I came across this thread, I was struck by the response to the original poster. Is it correct? In my book, if any variable power pack output voltage is fixed rather variable when tested with a multi-meter, something is wrong. If I am correct, what component, in the case of these Tyco power packs, is suspect?

Thanks, swede


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## Tom_C

I would expect the voltage to vary properly without a load, but to be sure I'd use a load and test it to be sure.

Pop the hood on it and post a picture of it's guts and lets have a look.


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## rrswede

Thank you for the response, Tom. 

Attached, hopefully, are two photos. The first photo shows the innards of a Tyco power pack with the cover removed. The second photo shows what is under the wiper assembly, primarily a rectifier assembly.

Depending upon where I place the ohm meter probes, I read a minimum of about 1.5 ohms (1 wire turn) to about 100 ohms (max reading).

swede


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## DonR

My guess is that the multiple wires that the wiper
sweeps are resistance with the lowest at the left
(off) end. You could test this with power disconnected
by setting your multimeter to ohms. Place one probe
at the left end...then slowly move the other probe across
the wires...you should see a gradually increasing
reading. If you get a reading otherwise the resistance
wires may be shorted or open. 

Have you checked that the wiper is making contact
with the wires?

DC power packs sell for 5.00 to 20.00 on Craigslist
or flea markets. 

Don


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## rrswede

Thanks for the response, Don. 

Yes the wiper arm does make good contact with the resistor wire and resistance readings gradually decrease as the wiper arm is moved from stop to full.

I understand the low value and low worth of these units but the fact that they don't function correctly and I don't understand the reason why promotes my interest. 

swede


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## Tom_C

Plug it in and slide your possitive meter probe along the wire windings.... carefully of course, and if you aren't comfortable testing hot circuits then don't do it! I would expect you'd see the voltage vary from one end to the other. But, it depends on the circuit. It's possible, depending on how it's built, that without load you'd read full voltage everywhere.

Hence, to be absolutely sure, you need to put a load on it and test it. Of course, if all of the units are exactly the same model then they should all show the same results, but it could be possible there are model variations (version 1.0, 1.1, etc) and so just put a load on it and be sure.


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## cid

I absolutely agree that without a load you cannot get a valid test. It appears that the circuit you pictured to us may be just an unregulated supply with a series variable resistance. No load = no current = no voltage drop in the resistor = full voltage at the output teminals. It works...


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## rrswede

Thank you Tom and cid for your additional thoughts.

Subsequent to my last post, went back to Waltr's response of 12/11/2012 and decided to try his suggestion. Did not have a suitable resistor on hand so wired three number 57 light bulbs in series hoping that would be sufficient for the load. With no load applied and sweeper arm just off the stop position, voltage was 18.2VDC. At full power it also measured 18.2 VDC. With the load applied, I initially did not measure the voltage change as the sweeper arm was rotated across the resistor, but did see a change in brightness. The test was performed a second time with a meter in place. With the sweeper arm just off the stop position, the voltage was 14.0 VDC and at full power the voltage was 16.8 VDC. A 2.8 VDC full range variation with the three lamps did not seem like very much to me. Perhaps the load was not sufficient.

A identical test was performed using a power pack that previously had passed my bench test. It was not a Tyco, it was a Bachmann. In fact, all the power packs that did pass my bench test were Bachmann and all the ones that did not, were Tyco. Coincidence or different construction??? Anyway, with no load applied and the sweep arm just off the stop, the voltage was 3.0 VDC and 17.9 VDC at full power. With the load applied and the sweep arm just off the stop, the voltage was 3.0 VDC and 14.8 VDC at full power. This is in line with what I expected. 

Wish a HO train layout was handy for testing the Tyco units for proper speed control. I still don't feel comfortable that these Tyco units are operating correctly.

Thanks, swede


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## cid

Hey, swede, with three #57 in series you can only pull 1/6A. Not enough. Try just one bulb. The 1/4 amp load should let your power packs operate normally. With two bulbs in parallel (NOT in series) you can get about 1/2 amp, pushing the 6VA rating. You can try that also. Good Luck!


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## rrswede

Thanks cid. Won't get to it till late tonight but will let you know how things turn out.

swede


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## DonR

The natural load for these small Power Packs is ONE
DC locomotive. If a usable oval is not available
place one in a cradle upside down and power it
with temporary wires. Then take your readings.

Don


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## Lemonhawk

If the voltage is changed with pot (variable resistor) then yes you need a load, if it uses a wiper on the transformer coil then you don't need a load.


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## rrswede

Thank you all for your assistance. 

While attending our neighborhood super bowl party, I was able to borrow a old HO locomotive that had been stored for many years. Cradling it as Don suggested, it did not take much coaxing to get it running using a Bachmann power pack that had passed my original bench test. The Bachmann provided a full speed range, stop, slow, medium and full speed. 

Knowing the locomotive operated, it was then powered up using three separate but suspect Tyco power packs. All three Tycos provided speed control, stop through full speed, but none provided good slow speed control. Each went from stop to medium speed and skipped the slow speed. 

Since finally getting it through my head (Lemonhead, your variable resistor vs coil wiper comment did the trick), I suspect if the applied load included track and a full set of cars, the locomotive would have gone through a slow speed range as well. Correct??

Anyway, I no longer think these power packs are defective and will not toss them without trying to find a home for them.

Again, thank you vey much. Another learning experience courtesy of this forum.

swede


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## Tom_C

rrswede said:


> I suspect if the applied load included track and a full set of cars, the locomotive would have gone through a slow speed range as well. Correct??


Perhaps, but I doubt you're going to get a lot of granular control from such a low-end PS.


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## Cycleops

Tom_C said:


> Perhaps, but I doubt you're going to get a lot of granular control from such a low-end PS.


Amen to that!


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## DonR

Those Tycos would be just right to power
turnouts, lights and other accessories.

Don


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## rrswede

At a low of 5 volt amps for an N scale power pack to 9 for HO, there is not a lot of flexibility for usage. They will find a home though.

swede


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