Accucraft K-27 head/marker light fail

maxi-model

maxi-model

UK/US/ROW steam narrow gauge railways 1:1
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I have a recently aquired 2nd hand electric Acucraft K-27, it has Sierra Soundtraxx card fitted. I accidently pulled off the smoke box front the other day. When I replaced it the head and marker lights no longer functioned in forward motion but the rear tender mounted light, only, still functions perfectly when the track current is reversed. I checked the wiring on the small circuit board, looks like Accucraft's standard 6v voltage regulator assy', mounted in the smoke box and the only thing amiss was one of the legs on the cylindrical object ( sorry I have virtualy zero understanding of these things other than simple wiring) on the board had come adrift. I soldered this back into what appeared to be the correct position on the board. But still no front head/marker light function. All the wiring to the head and marker lights seems ok with no breaks. Any ideas what is going on here and what I might need to do to fix ?

I include an image to aid with identification of components. I would much appreciate your ideas on what I need to do to fix. I'm wondering if I need to replace the lights wholesale or might one of you eletrickery minded souls have spotted something like a diode thingy that might need replacing. Max.

20180904_200510.jpg
 
My understanding is that it is indeed 6 volts, and the components are a 6 volt regulator (3 terminals with a heat sink), a full wave bridge rectified (to fix the polarity to the regulator) and a filter capacitor (the round can).

Usually you cannot remove a wire from a circuit board without damage...

The correct debugging is to:

1. validate the full wave bridge is receiving track power
2. validate the output of the full wave bridge
3. validate the output of the bridge is applied to the regulator
4. validate the output voltage of the regulator.

The filter capacitor might be damaged, but normally would not result in zero output.

You can check the circuit and connections on the regulator by looking up the part number. It is probably a 3 terminal positive voltage regulator, in the LM78xx series.

Look on the regulator for letters and numbers... the 4 digit number is probably a date code... the other letters and numbers are the mfg and part number.

Greg
 
Wot Greg says..
Plus.. I would doubt the capacitor (big cylinder) would be mounted 'above the board' and sitting (almost) on top of the circular bridge rectifier..
Perhaps the wires were spread-out, and it connected to one of theose holes in the edge of the board? - I should be obvious if pone of these has a gob of solder on the back..

Did any other wires come lose?
 
It really seems that the electrolytic is a radial lead, not axial lead. in any case the 3 terminal regulator has input, output, and ground.

The electrolytic capacitor is probably on the input side, i.e. positive to the positive output of the full wave bridge, and negative to the negative.

The full wave bridge should have 4 leads, marked ~, ~, +, - ... the ~ is a sign normally for AC input, but in this case, they are both connected to the track pickups... the + and the - are the outputs.

7.-Circuit-Diagram-of-Fixed-Positive-Voltage-Regulator.png


C1 is your electrolytic capacitor... the C2 capacitor is not in your circuit.... also note that this is for a 12v regulator, you have a 6v one...

Greg
 
Hi Max
Oooops!
Have you tested to see if there is power actually coming to the board when in forward?
If you have a rolling road or rolling road blocks, just pop her on (you will need to have power (over about 8v or so) also running to the tender and have it linked up to the loco as voltage comes from the right hand side of the loco and left hand side of the tender and use the connector to pass this to the loco) and use a multimeter to test the wires that come from back in the boiler.
I think that the power wires have a pull off/on connector to the PCB

If there is no power coming to the board, then the problem is back in where the feed from the wheels and tender joins up.

If there is power then there might be a wire that is shorting from the lights OR .... a disconnected wire/break on the circuit board/pcb. As it is a simple board it will not be hard to fix. OR a failed component.
When I tested her, before selling her to you, the lights were working and the components (that I can see in the photo) do not look damaged etc.
It will probably be a break in power feed, hopefully not back in the boiler.

When you accidentally pulled the smokebox door off, did it yank the whole lot of wires etc, out of the boiler?
 
Thank you all for your responses. Looks like I am going to have to go through a process of elimination. Yes I have a rolling road and a multimeter - just got to learn how to use them ;) I may well post the specs printed on the components on the board to get some directions what to shop for if needed. Pity the 6v voltage regulator board for this loco is listed out of stock on the Accucraft E-Store. The PCB itself looks fine so it might just be a case of dropping in the required component(s) as required. Max
 
Greg Elmassian said:
LM7806 regulator can be had for under $1 here... 45 cents actually...Greg
Click to expand...

Thank you Greg for your information. It helped greatly with working out what components to source in the UK. The circuit diagram was particularly helpful. Yes those bits on the board - full wave rectifier, voltage controller, and capacitor are pennies. I'm not sure if validating the 3 components on the board are within my limited abilities.......and patience.

I now know why I was scratching my head over the the rear light still working - there is another PCB with voltage regulation in the tender. Doh !

After a long conversation with an understanding Creaky Beaver (Mike many thanks) the initial plan is to chase a possible short and blown bulbs up front. If that shows there is no problem there then it's pobably replace the do-dads on the PCB or even get a replacement board made up. The "fully loaded" board is shown on the Accucraft store at $9 plus shipping but is out of stock - it may be quicker and cheaper to get a possible source to make up here in the UK if the PCB is not reusable. I might get me a few spares. Again many thanks to you all. Max
 
maxi-model said:
The "fully loaded" board is shown on the Accucraft store at $9 plus shipping but is out of stock - it may be quicker and cheaper to get a possible source to make up here in the UK
Click to expand...
There's no "may be" about it. I recently had to purchase a critical but only $10 part from Bachmann USA that was unavailable over here. Shipping was almost $20 and there's always a charge for currency exchange in the rate you pay.
 
Neil Robinson said:
There's no "may be" about it. I recently had to purchase a critical but only $10 part from Bachmann USA that was unavailable over here. Shipping was almost $20 and there's always a charge for currency exchange in the rate you pay.
Click to expand...

Yep, I totally concur.
As Bachmann has more or less completely pulled out of 1:20.3 and the really important spares for the various FN3 scale locos on the Bachmann USA site have sold out, never to be rerun, it looks like home made replacements, where feasible, are the order of the day..... unless some other company steps in.
 
Hi John............. exactly!!!!!!
I have a sneaking suspicion that Max maybe in touch! :cool:
 
Ooooooh ! I like the look of that. Would it be possible to have a word with you John S ? :wasntme: Max
 
Hi John and Max
John:
The 'extra' cable goes back to the cab light.
The rear light on the tender has its own regulator board
Max:
You might find this article interesting as it describes the replacing of the Accucraft tungsten bulbs with leds. It also explains the original wiring etc
LED Locomotive Headlight Replacement in Model Trains - Articles
 
John S said:
Been for a rummage, can make 4 in total…. will send one of those conversation thingies............
Now got a decent roll of solder at last, can press on with several jobs that are outstanding, have a few of Mike's (Beaver Creek) to complete first, I'll let you know when I can put them together.....
Click to expand...

Hello John. Do I take that to be an offer to produce a replica Accucraft voltage regulator board.....or two ? :) Please contact me when convenient. That would help a lot, even if only as an insurance policy.

Mike, thank you for the article on the LED fitments - I think I won't tempt fate and stick with the incandecents. Then again I might tempt fate by going over to battery power on this one, given it is an older version with pick ups only on one side on the drivers and the other on the tender wheels - It has exposed all sorts of fun and games on my line, unlike all the others (Bachmann) that use all wheels both sides to pick up. As I have one battery loco to accompany the 16 mm fleet I suppose I'd better do one for the 15 mm stuff for when I'm feeling lazy. Anyhow, the Sierra sound card might appreciate a better regulated flow of electrons than it is getting at present - that grade crossing whistle is getting quite annoying. Max
 
maxi-model said:
Anyhow, the Sierra sound card might appreciate a better regulated flow of electrons than it is getting at present - that grade crossing whistle is getting quite annoying. Max
Click to expand...

Yeah I imagine that it is!.... but you can program the grade crossing auto-trigger to have lower sensitivity so that it will not 'sound-off' so frequently if at all!
On the Sierra board are two little buttons...these are used to program all of the sounds and the triggering. The manual shows how to do it. It is a bit fiddly but not difficult.... it will help with the annoyance....:mad::mad:
 
Greg Elmassian said:
My understanding is that it is indeed 6 volts, and the components are a 6 volt regulator (3 terminals with a heat sink), a full wave bridge rectified (to fix the polarity to the regulator) and a filter capacitor (the round can). Usually you cannot remove a wire from a circuit board without damage...
The correct debugging is to:
1. validate the full wave bridge is receiving track power
2. validate the output of the full wave bridge
3. validate the output of the bridge is applied to the regulator
4. validate the output voltage of the regulator.
Greg
Click to expand...

Ok have done as you suggested -

1. Full wave bridge is receiving track power @ 12 v
2. Full wave bridge is outputting 13 v
3 Output 12.5 v being applied to voltage regulator
4 Output voltage regulator.........0. I think we have the root if not the source of the problem.

I checked the capacitor and it was also showing 12.1 v across its terminals on the board - noted there was a fracture in copper circuit that had detached from the board at the bottom of the disturbed (and resoldered) leg of the capacitor, I cleaned up and put in a little solder to fix.

Naturally no output on the light circuit. Put the multi meter across the light terminals, set for ohms, it just registered -1, which I understand means no short (Have I got this right Mike/Greg ?)

I think best practice will be to junk the board and replace. John S has very generously come to my aid and produced a small batch of replacements. Looking on the positive side this has all been very helpful so far in demystifying this stuff and getting me over my paranoia over prodding about in these things. You'd think I'd have got over that after 15 years - But then I've never had a £1,5000 electric loco before now :sweating::worried: Max


A little diagram that may irritate/confuse in equal measures. It's so I can understand where i'm prodding

20180911_111356.jpg
 
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