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Bachmann Spectrum 80 ton three truck Shay electrical faults

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    June 2020
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Bachmann Spectrum 80 ton three truck Shay electrical faults
Posted by Lastspikemike on Monday, March 22, 2021 6:38 PM

fixed the gears. Well, still needs one new gear in the main center truck but that can wait since one main axle is driving as are all the other four. 

Now for the weird electrical faults.

Locomotive powers up and responds to DCC power and sound features.

Once it moves it intermittently stops for no apparent reason. 

The symptom is a static crackle over the speaker then silence and no movement. 

Running at full speed (step 128) and the crackle is still there but the locomotive mostly powers through. Slow speeds not so much.

Pressing down on any of the trucks with a finger on the appropriate part of the locomotive restores power. Pressing gently on the right side of any of the trucks restores power, even pressing on the driveshafts seems to be enough. 

It seems to be a pickup problem from wheel to truck pick up. All is clean and lubricated. The truck electrical contacts are all clean and de-oxidized. Plugs have been removed, cleaned with contact cleaner and replaced into the sockets. No obvious wiring continuity issues there.

My plan is to install an 8 pin dummy plug and see if it might be the decoder. Have to get one first.

Any ideas welcomed. The previous owner did a really great paint and decal job so I'd like to fully restore this interesting locomotive.

Alyth Yard

Canada

  • Member since
    February 2002
  • From: Reading, PA
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Posted by rrinker on Monday, March 22, 2021 9:23 PM

 Custom painted you say? Might have paint where paint shouldn't be, deoxit won't clean that off. 

 Don't have any of those, so I'm not sure how the power gets fromt he truck to the loco - are there wires to the truck or does it rely on some sort of contact surface like the bolster contact of an Athearn loco? If it's wires - are they secured to the trucks with thoise silly plastic caps? It's not uncommon for all but one of the strands in the wire to break off right at the plastic cip, where the insulation of the wire ends, leaving it literally hanging by a thread. Also those palstic caps are unreliable - solder the wires to the tabs. If there's actually some sort of friction contact instead of wires, it's pretty easy to get overspray in those kind of areas if not careful, and it doesn;t take a full coat of paint to cause contact issues - even a few drops of overspray can be thick enough to cause an intermittant contact.

                                         --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by snjroy on Tuesday, March 23, 2021 10:39 AM

I'm glad you progressed with the gears issue. 

I would suggest doing the "glass" test, where you put the loco on a flat surface to see if all the wheels touch the surface, if you have not done so. If they don't, power pickup may be affected. The loco may also derail on curves and switches.

I agree that paint could be a factor. If you are confident that the gears have been installed properly, it just might be a question of breaking in the loco, that is, breaking in the gears and getting the paint off from the moving parts and power pickups. But to be honest, I would fix all of the gears first, then break it in.  This loco was designed as a three truck so having gears that are not operating may lead to problems down the road.

My opinion, your choices, as someone here used to say (I can't remember who!)

Simon

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Posted by Lastspikemike on Wednesday, March 24, 2021 9:43 AM

Box says it's the Weyerhaeuser version. Model number says DC with 8 pin DCC ready. So, diy sound decoder  install. Will investigate.

Glass plate test is an excellent suggestion, thanks. Trucks do look a little wonky from the upside down view (of which I got a lot of during the gear replacement saga and that's just the lead truck!). 

Possible paint contamination of the brass side frames is also a helpful idea.  

Amazingly, there are no track power pickup wipers on either the truck axles or any of the 12 drive wheels. Therefore, all power must pass from wheel treads through the axle ends into the "bearing surfaces" which are just cast in holes in the side frames. Polarity isolation is effected by a plastic truck bolster and two multi part plastic end frames connecting the two side frames, all held together by just  two tiny screws. The total current must pass through each of these tiny screws onto flat spring brass contact strips that carry current up to nickel silver (apparently) rubbing faces which are each wired to the (Bachmann standard) 4 pin and 2 pin plugs on the tender harness).

I'll check if it runs better in DC only mode. 

Alyth Yard

Canada

  • Member since
    June 2020
  • 1,931 posts
Posted by Lastspikemike on Wednesday, March 24, 2021 2:48 PM

It passed the glass surface test. Each truck is level and contacting the glass equally except for slightly more weight on the smoke stack end of the boiler. Makes sense since the rear of the locomotive sits on two trucks.

There is an apparently steady improvement in performance. I used the Atlas contactalube on the axle ends and the contact wiper plates and strips. Just tapping the table top beside the locomotive is enough to get it going. 

My current working theory is poor conduction from axle ends to side frames. Running more may just solve this.

Alyth Yard

Canada

  • Member since
    February 2002
  • From: Reading, PA
  • 30,002 posts
Posted by rrinker on Wednesday, March 24, 2021 9:28 PM

 It sounds liek this is maybe the MDC Boxcab if I understand your decriptions. Brass tabs on the underside of the loco that rub on screws on the trucks to transfer power from the swiveling truck to the loco chassis. This was a bif of a weak spot on the MDC loco, keeping those screw heads clean and the tabs as well pretty much requires dropping the trucks to get at it. And when left to sit, the brass naturally tarnishes. Some running so the screw heads and wipe back and forth on the tabs probably helps a lot to get them clean.

                                    --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

  • Member since
    June 2020
  • 1,931 posts
Posted by Lastspikemike on Thursday, March 25, 2021 9:45 AM

Similar idea. Instead of screw heads, Bachmann elected to use springy brass contact strips secured by the side frame assembly screw and alignment pin on each cast brass side frame. The pressed in bump at the top end of the contact strips rubs on silvery metal pads glued to the underside of the locomotive, coal bunker  or tender frame in those three places. The pair of pads are separated from each other by an insulating strip between the pads and are wired to the appropriate tender plug (all black wires). The brass strips reach up from the truck frames. 

Presumably, Bachmann didn't design this Shay from scratch but acquired some moulds from an earlier model maker.

My current working theory is the contact points between the axles and the truck side frames. These seem incapable of making really good contact. A keep alive seems a logical solution. 

Testing and investigation continue. Once the power problem is resolved I'll get the remaining broken gears replaced. Only two axles aren't driving now. One with a split plastic gear (to be replaced with a NWSL metal gear) and the very front axle needs the drive gear pressing onto the drive shaft by a nanometer or two more in order to engage reliably with the driver gear. That gear can be squeezed a bit further onto the shaft  without removing the shaft from the truck frame.

Alyth Yard

Canada

  • Member since
    February 2002
  • From: Reading, PA
  • 30,002 posts
Posted by rrinker on Thursday, March 25, 2021 1:11 PM

 If one gear already cracked - might as well save yourself some trouble and get a complete set, the others WILL crack eventually. This is the approach I've taken with all my P2K locos, although the Athearn replacement gears are pretty inexpensive compared to NWSL metal gears.

                                   --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

  • Member since
    June 2020
  • 1,931 posts
Posted by Lastspikemike on Thursday, March 25, 2021 6:38 PM

NWSL only sells sets of 6. I've a mind to leave the tender truck gears until one actually breaks. There's no economies of scale doing more than one needs to. Each individual truck has one drive shaft with two gears. No sense taking out the drive shaft and only replacing one gear but equally, no sense fixing what ain't yet broke. 

Alyth Yard

Canada

  • Member since
    June 2020
  • 1,931 posts
Posted by Lastspikemike on Monday, March 29, 2021 10:42 AM

Soundtraxx plug n play 3TSLC correctly installed with hard wired speaker in the coal bunker. To bypass this decoder I need to install connectors into the speaker wires in order to remove the decoder from the tender. Not sure why adding these aren't a routine step to facilitate servicing or updating of the locomotive but I guess I'm about to find out. 

Capacitor on the light board is still in circuit but Soundtraxx doesn't say this needs to be removed. They assert this decoder simply plugs in. 

Interestingly, the more I run this locomotive the less power interruptions it experiences. I put conducta-lube into the ends of the axles a few days ago. I haven't run it much because the big layout is currently dismantled. Before I decide to "fix" this electrical problem and possibly create other difficulties I plan on running this locomotive a lot further.

Alyth Yard

Canada

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