Quote from: jbrock27 on December 06, 2015, 09:24:49 AM
Awesome Glen!  Thank you.

You are welcome jbrock27.  Glad to help when I can.

I am curious as to whether MRC ever corrected this defect.  I see they are still selling the MRC1370.  It would be interesting for owners of these units who are reading this to open them up and see, and add the fix while opened if desired.  I emailed MRC asking, but based on their prior lack of response to my queries I doubt if I will hear from them.

Also those who do install the fix to report on the starting and slow speed running improvements.  I know this made a huge difference for the MTL Z Scale F7.

Quote from: jbrock27 on December 04, 2015, 08:23:37 PM
Thanks much for your efforts and help! :)

Here are the photos you asked for, these are better for those who wish to fix their own MRC1370 power packs.  Don't know if MRC would be willing to correct this manufacturing flaw on existing units, but one could ask them.  I approached MRC about this 10 years ago, they ignored the problem.  I guess, like Volkswagon and their Diesel emissions, they figured no one would notice.



Above is the tool to undo the 'security' screws.  All it takes is a needle file to cut the slot into a regular screwdriver. 
BE SURE TO UNPLUG THE POWER PACK FROM THE AC OUTLET BEFORE DIS-ASSEMBLING THE CASE!



Above:  Although not necessary, if you take a defective unit apart enough to lift out the printed circuit board (PCB) you will see an empty component location labelled R1.  This is a little to the left of center.  You have to pry up the heatsink (the flat metal plate) to make the external knob slip off the shaft of the speed control, then unscrew the large power transistor from the heatsink.  Do NOT remove the white thermal grease; this is needed to transfer heat from the transistor to the heatsink.



It is not necessary to remove the PCB to install the fix on the solder side of the PCB which is accessible as soon as the 4 screws holding the box together are removed.  The absence of R1 can be seen by the lack of wires protruding from the solder joints at the empty R1 location.  Solder in a new resistor as shown.  Anything between 5000 and 10000 ohms will work.  Be sure to use insulating sleeving on the resistor wires so they do not short circuit to anything else on the PCB.  The resistor wire soldered at top center of the photo can connect to either of the pads (but not both at the same time!) to which the red transformer wires are connected.  The choice of which pad is determined by the desired phasing as discussed in earlier posts.  Only matters if you run a train over blocks powered by more than one power pack.

You can see the fix is quite simple.  So why could MRC not have done this during manufacture?

Quote from: jbrock27 on December 04, 2015, 07:14:21 AM
but I was hoping for some pics of the guts of the power pack.  Had you taken any of the work on it or no Glen?

No, it was pretty straightforward, but I still have the cheater screwdriver and the power pack is around here somewhere.  Will get some photos this weekend, and now that I learned how to use photobucket will post them.

MRC1370 Manufacturing Defect and Solution



Above: The yellow trace is a MRC1400 working properly at low speed and outputting mostly half-wave rectified with low voltage pulses in the gaps between the main higher voltage pulses.  As the throttle is advanced both the low and higher voltage pulses increase, but the low voltage pulses increase faster until at full speed all pulses are the same voltage, ie full-wave rectified.  The half-wave causes the motor to generate higher torque at low speed.
The blue trace is the MRC1370 with the manufacturing defect.  It outputs full-wave at all voltage (speed) levels.  With the fix shown below it will instead perform like the MRC1400 (and others) as intended.

Above is the MRC1370 schematic showing where the missing R1 is connected in error.  Install a 5% 5600 ohm 1/4 watt resistor at the missing R1 location.  Either cut the trace where shown or lift that lead of the new R1 out of the pcb and connect instead to the diodes AC input (transformer secondary).  Which wire of the transformer secondary is usually not important unless you run more than one power pack on the same train and need to have all phased the same way.  Use oscilloscope or experiment with phase to ensure locos do not speed up when straddling blocks powered from two separate power packs.  When properly phased all power packs will source the main pulse at the same time, ie on the same half cycle of the AC powerline. 

Quote from: jbrock27 on December 03, 2015, 09:14:52 PM
It is the same thing there bro.

Not sure why, they work for me but then I am the moderator.
Do you have a yahoo account?  Maybe yahoo denies access to groups unless you register on yahoo first.
Do you know if there is any way to attach this file here?  When I try I get a message something like "Upload buffer full" and the file is only 110KB so should work.  The pics are embedded in the Word file and I don't think I can extract them, and as I said the originals are lost.

Quote from: jbrock27 on December 03, 2015, 08:28:44 PM
"Files" (at least the one I see which is to the left of "About") is grayed out and nothing happens when clicking on it.

Try the other website Locomotive Maintenance, that one does not need moderator approval for membership.

Quote from: jbrock27 on December 03, 2015, 12:37:57 PM
but how come I only am seeing 2 pics?

Sorry, was in a hurry this morning to get to work.  Those are the groups home pages.  Click on 'Files' near the top and then to the MRC1370 file.

jbrock27
The original pics were lost in a hard drive crash long ago, but was able to recover the .doc file from a forum.   Being new to this Bachmann forum cannot figure out how to attach it.  However, the file with the pics can be seen at either

https://groups.yahoo.com/neo/groups/Z_Scale_Electronics/info

https://groups.yahoo.com/neo/groups/MTL-ZScaleLocomotiveMaintenance/info

I tracked down a thread on Trainboard from 2009 where a fellow named Glenn said:

QuoteWhile the MRC 1300 is OK, avoid the MRC1370 at all costs. A manufacturing defect on the MRC1370 results in full wave power at all speed settings, unlike the MRC 1300 with correct half wave output at low throttle settings.

That's not a manufacturing defect. All it means is the MRC 1300 use half-wave rectified AC on it's track output, like the older Tech II power packs, while the MRC 1370 uses full-wave rectified AC, resulting in a smoother DC output on it's track output. There's a fairly decent explanation of the difference here: http://www.radio-electronics.com/info/circuits/diode-rectifier/full-wave-rectifiers-circuits.php

All it really means is the MRC 1370 is actually providing more power at a given throttle setting than the MRC 1300, while the pulsing effect of the half-wave output of the MRC 1300, like the Tech II's, may give better starting performance to older locos.

Why someone who doesn't understand something as basic as half-wave vs full-wave rectification is looking at things with an O-scope beats me.

Len
[/quote]

Len,
You are correct that half-wave gives better starting performance.  Also better slow speed performance.  Because there are only 60 half-wave sinusoidal pulses per second (with intervening gaps) as opposed to 120 PPS full-wave (assuming a 60HZ AC power source) each pulse must be a higher voltage and current for the same motor speed.  This causes the motor to output a higher torque at that speed than it would have at 120 PPS.

The MRC1370 did have a manufacturing defect.  This was back in 2002 for the circuit board identified by the numbers PC-1370M-1  and 16-01-01.  MRC might have fixed the problem since then; I don't know.  What I do know is that a MRC representative told me in a telephone conversion that the 1370 should should be half-wave output at low throttle settings like other similar MRC products, and seemed surprised when I reported that it did not.

If you have one of these units you can determine (and fix) any defects by opening the case, unplug it from the AC outlet first.  The 'security' screws are easily overcome by filing a notch in the blade of a regular flat screwdriver to make it fit the screw.

Look at the circuit board to see if there is an empty component location labelled 'R1'.  The defective boards have an error in the copper etch that connect one end of R1 to the output of the bridge rectifier.  This resistor should have been connected to one of the AC terminals of the bridge rectifier instead.  Since the manufacturer chose to leave out this resistor it is obvious that the manufacturer was aware of the problem and decided to ship the product anyway.

If your R1 is missing, fix the problem by installing a 5% 5.6 kilohm resistor, 1/4 watt is fine, one lead into the pcb hole that connects to the wiper (center terminal) of the speed control.  Leave the other lead of the new resistor out of the pcb, instead use a wire to connect it to one of the AC input terminals of the bridge rectifier.  Which AC input terminal does not really matter unless you want ALL your power packs to be phased the same way, so that when the locomotive crosses between blocks that are each driven by separate power packs it does not temporarily speed up by receiving out-of-phase pulses (temporary full-wave while stradding blocks) from the two separate power packs.  If you do not have an oscilloscope you will have to determine the phasing by experimentation.

Now your MRC1370 should output half-wave at slow throttle setting, increasing gradually to full-wave as the throttle is advanced to full speed like it was designed to do.  By gradually I mean that the suppressed sinuoidal pulses in the 'gap' between the main pulses will increase in amplitude relative to the main pulses.  Your locomotives will now run even smoother at slow speed.

And by the way, I am the 'Glenn' you refer to in the above quote; and my occupation for the last 40 years has been electronic design engineering.  I do know the difference between half-wave and full-wave rectification

Regards,
Glen