problem with MRC1370

[frenchie]

hello everyone,

 

I am new on this forum so let me introduced myself first. I am 40 year old and moved from france to canada in 2007. I brought with me my teenager electric train (mostly Jouef brand) and I am presently put it back together for my son. I had to rebuy power supply since the european ones are running on 220V. I bought a Railpower  1370 which was working fine until now.

so here is my problem that require a bit of electronic brain storming but my knowledge in this field is weak. The DC does not change like it should between upon action of the potentiometer. voltage varies between 15 and 16.2V depending on the potentiometer position instead of 0-15 or so... A shortcut might have occurs at the connections while I was testing some LED...my fault.

the AC is fine and set to 19 V. The reverse switch function correctly.

Since I have lost the receipt, I have opened the transformer and I am presently checking the electronic elements one by one using a digital multimeter. Beyond the fact that I could buy another one I would like even more to understand what s wrong in the electronic

- the diodes looks all fine as well as the resistances. one condo looks fine (10 microF). The potentiometer looks fine also( R varies between 28 Ohm to 19kOhm).

-I did not test the transistors(2x)  nor the Triac yet thinking that your advice and comments would be of interest before going further.....I did not test the flat chemical condensator (if I am correct on this one)

 

cheers

 

Francois

 

[richhotrain]

Francois,

Welcome to the Forums.

I suspect that you may have shorted the DC portion of the power pack from your discussion of the problem.

I have had four MRC Railpower 1370 units on my layout for the last 7 years and have not had a single problem.

Rich

[rrinker]

 WIth no control over the output, the problem is almost certainly in the transistors or triac. One of these has failed closed and is allowing full power with no respect for the potentiometer position.

                  --Randy

 

[frenchie]

thanks Randy: it appears that the two small ones are good but the big one(TIP 142)  is dead! I ll change it and let you know if if this works...

 

thanks again

 

francois

[richhotrain]

Interesting.  This interests me because I have four of these exact power packs strung around my layout.

How difficult is it to repair this problem?

Being electronically illiterate, I would have assumed that the power pack was wrecked and junked it.

Randy, what do you think caused the problem?

Rich

[rrinker]

 Probably shorting the output one too many times. Unless they really changed what's inside those things, they don't have a very fast acting circuit breaker (if the 1370 even has one), certainly nothing like found on DCC systems.

 This only should affect the variable DC output, so if you are using them for the AC outputs, no need to worry. I've never taken one apart so I'm not sure how well teh components are laid out, but it should be simply a matter of unsoldering the failed transistor and repalcing it with the same or equivalent replacement. 3 wires and perhaps it's screwed to a heat sink. Getting the case open is probbaly the tricky part since they don't make it easy to get inside - part of the requirement for UL listing.

                   --Randy

 

[richhotrain]

rrinker

. Getting the case open is probbaly the tricky part since they don't make it easy to get inside - part of the requirement for UL listing.

                   --Randy

 

Thanks for that explanation, Randy.

Interesting comment on the difficulty of getting inside the case.  I always wondered why they make things so difficult, but never realized that it is a requirement for a UL listing.

Rich

[frenchie]

indeed opening the transformer was the easiest part. It took me 30 s to make the tool.
take a small-medium used or cheap flat screw driver, and with a dremel equipped with a metal disk, make a slit in the middle of the flat screw driver: your tool is ready....

I havent received the TIP142, but yes randy is right: three leg to solder and one little screw for the heatsink....


that said I havent repaired it yet!!! Il let you know when ready

cheers
francois

[tstage]

richhotrain

rrinker:

. Getting the case open is probbaly the tricky part since they don't make it easy to get inside - part of the requirement for UL listing.

                   --Randy

Thanks for that explanation, Randy.

Interesting comment on the difficulty of getting inside the case.  I always wondered why they make things so difficult, but never realized that it is a requirement for a UL listing.

Rich

I had to open my MRC Railpower 1370 one time and used a modified screwdriver to do it.  Having a plethora of small Sears Craftsman screwdrivers (1/8" flathead) laying around, I filed a groove in the middle of one about 1/16" wide.  It worked like a charm and I removed all 4 screws with it.

Tom

[tstage]

frenchie

indeed opening the transformer was the easiest part. It took me 30 s to make the tool.
take a small-medium used or cheap flat screw driver, and with a dremel equipped with a metal disk, make a slit in the middle of the flat screw driver: your tool is ready....

francois,

I neglected to see your post before responding to Rich's and Randy's comment.  Looks like you did pretty much the same thing I did with a small flathead screwdriver.  Mine, however, just took a little longer to modify.

Tom

[rrinker]

 There are places you can buy a set of all those really odd bits that they fasten consumer stuff together with so you can;t just simply use a screwdriver on it - These don;t sound too tough, but some of those varieties would be a real challenge to try and make out of a regular bit and a Dremel.

                     --Randy