Author Topic: Digitrax Throttle Capacitors  (Read 850 times)

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karman1970

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Digitrax Throttle Capacitors
« on: April 16, 2021, 04:29:24 PM »
+1
Just got a new and unused DT300 off eBay yesterday.  I plugged it in to my DCS50 and was greeted with a blinking screen.  Reached out to Digitrax and they indicated it was a capacitor issue - and that they no longer will repair the DT300.  Anyone have any advice on what capacitors I should get to try and repair it myself?  My searches of the internet have turned up that it is probably a 4.7 uF 25V SMD, but I don't know what I should look for besides that.  I've found MLCC models, aluminum something or other, and other variations I can't remember.  As long as I can get it attached to the board and the capacitance and voltage match, will I be ok?

Thanks

wvgca

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Re: Digitrax Throttle Capacitors
« Reply #1 on: April 16, 2021, 05:29:15 PM »
0
you would be best off contacting others that have had the same problem, and fixed it ...
if you can find the exact part number and where they got it, it will be less of a headache ,,
you should also contact the seller of the throttle and ask for a partial refund because of the errors ./

peteski

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Re: Digitrax Throttle Capacitors
« Reply #2 on: April 16, 2021, 05:30:11 PM »
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That capacitor value you mentioned is in fact most likely a generic aluminum electrolytic capacitor.  SMD indicates it is surface mount package.  It will look similar to these, although yours will likely have different shape:



Since the cap has almost completely hidden leads in a stiff plastic base, trying to just unsolder it  would likely result in the solder pads being pulled off the PC board.  order to remove the bad one you will likely have to carefully physically remove it (cut it away piece by piece) until you expose the leads and solder pads.  Then carefully unsolder what is left on the PC board.  I hope you have a temperature-controlled iron. I would not set it any higher than 700 deg. F because the copper traces on the PC board are likely very delicate. Adding some solder and flux to the leads before trying to unsolder them will aid in quick removal. Then it would be beneficial to clan the solder pads. Use solder wick.  These caps are polarized, so make sure ou note the polarity of the cap. Sometimes that is not indicated on the PC board.

Soldering the new one will be tricky because only very small end of the lead is exposed.  Those are meant to be machine soldered using hot air.  I woudl put some flux on the cleaned solder pads, then place the capacitor over the pads (make sure the polarity is correct), then place some solder on the tip of your iron (hopefully it has a fine tip)., then (while holding the capacitor so it doesn't move) touch the tip with solder to the capacitor's exposed lead.  The flux you applied earlier will hep in conducting the heat to the hidden portion of the lead, and to the solder pad.

That should do it.

The SMD 4.7uF 25V are very popular caps - should be available from any electronic parts supplier.

Here is a range of those caps available from Digikey.  Not sure how long that link will work.  While any of those should work electrically, there are variations in physical dimensions (some are taller, some shorter). Make sure to measure yours to find an exact match.

https://www.digikey.com/en/products/filter/aluminum-electrolytic-capacitors/58?s=N4IgjCBcoGwJxVAYygMwIYBsDOBTANCAPZQDaIALAAxwDMdIAuoQA4AuUIAymwE4CWAOwDmIAL6EwcABwJoIFJAw4CxMiCpNWHSNz5DREkACYqFOcjRY8hEpHIUAdAHYABAFaAYlpDtOAVUF%2BNgB5VABZXHRsAFdeXHFCU2cLBSsVW3VjAFZXADUfP11A4LDI6LiEowBabMQ0pWtVO3JjJhq2%2BUU%2BGOb1OsYxIaA
« Last Edit: April 16, 2021, 07:39:38 PM by peteski »
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karman1970

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Re: Digitrax Throttle Capacitors
« Reply #3 on: April 16, 2021, 06:01:35 PM »
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Thank you.  Yes, I have found a few threads on forums regarding this issue, but all from 5 plus years ago.  Most of them ended with no resolution or a trip to Digitrax for repair, which doesn't help me.  I'll open it up and get some measurements off the suspect capacitors and try to find a part number on Mouser or Digikey with the same dimensions.  I'm decent at most model railroading soldering stuff (rail joints, feeder wires, wired decoders), but this will be my first attempt at tackling PCB electronics.  Seems like a good excuse for a new/better soldering iron :)

John

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Re: Digitrax Throttle Capacitors
« Reply #4 on: April 16, 2021, 06:17:35 PM »
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If you fix it, please document your progress with pictures and post them here for others to learn from .. thanks

Point353

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Re: Digitrax Throttle Capacitors
« Reply #5 on: April 16, 2021, 08:42:04 PM »
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Just got a new and unused DT300 off eBay yesterday.  I plugged it in to my DCS50 and was greeted with a blinking screen.  Reached out to Digitrax and they indicated it was a capacitor issue - and that they no longer will repair the DT300.  Anyone have any advice on what capacitors I should get to try and repair it myself?
Will Digitrax tell you what the type, capacitance value, voltage rating and case size is for the capacitor(s)?
Or, will they tell you which manufacturer's part number(s) they were using for replacements?

peteski

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Re: Digitrax Throttle Capacitors
« Reply #6 on: April 16, 2021, 09:39:23 PM »
+1
Will Digitrax tell you what the type, capacitance value, voltage rating and case size is for the capacitor(s)?
Or, will they tell you which manufacturer's part number(s) they were using for replacements?

That would sure make finding the replacement easier, but if you follow that Digitrax search result link, there aren't too many size variations for the specs given.  And I doubt that we would have to worry about things like the cap's ESR value.
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karman1970

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Re: Digitrax Throttle Capacitors
« Reply #7 on: April 27, 2021, 05:07:41 PM »
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Thanks for the feedback.  I reached out to Digitrax.  Waiting on a response, but I'm not hopeful since it is an unsupported product.

I guess I probably need more posts before I can upload pictures.  However, based on the one description of repairing these things that I can find, I'm pretty sure I identified the two suspects.  They are of the cylindrical, electrolytic type.  The only two on the board.  I'm a little relieved by that.  Feel like it gives me more meat to work with than if they were the microscopic ceramic type ones I've been watching Youtube videos on, although they are still really small.  I can barely see what looks like the solder pads without using a magnifying glass.  Any opinions as to whether I should stick with a direct replacement, go to something with leads, or some other type that possibly isn't electrolytic?

mu26aeh

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Re: Digitrax Throttle Capacitors
« Reply #8 on: April 27, 2021, 05:12:07 PM »
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Digitrax reply -  Why fix an old, outdated, unsupported model when you can have the voluptuous curves of our new DT602 ?

peteski

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Re: Digitrax Throttle Capacitors
« Reply #9 on: April 27, 2021, 05:44:02 PM »
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After 25 posts, you will have full access to the forum (uploading photos, etc.).  Check out the FAQ section of the Admin board.

As far as rework goes, as I mentioned, it will require some precision soldering (the way I would approach this is on my earlier post).

There should be no need to change the capacitor type. Electrolytic caps have been the mainstay of electronic devices from the very early days of radio, and are still widely used.  But you could also replace them with another type.  Safest and most reliable would be multilayer ceramic caps. Those are also non=polarized, so no need to worry about polarity.
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reinhardtjh

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Re: Digitrax Throttle Capacitors
« Reply #10 on: April 27, 2021, 06:32:17 PM »
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Thanks for the feedback.  I reached out to Digitrax.  Waiting on a response, but I'm not hopeful since it is an unsupported product.

If Digitrax isn't helpful (and I'm not very hopeful based on other responses) then you should check at the Digitrax GroupsIO mailing list.  Others there have done self repairs on most of Digitrax's products.  It's probably in the archives somewhere that someone has replaced the caps on a DT300.  The DT300 was a most desired throttle by some as it sits right int he middle in functionality between the DT100 and the UT4.  I know of several on the list that used to go to far lengths to get more of the throttles.

Groups IO: https://groups.io/g/Digitrax-Users

I just did a search of messages for "DT300 cap" and there are quite a few.  One thread as old as 12/15/2000

One really specific thread is https://groups.io/g/Digitrax-Users/message/220241  It is recent, being posted 08/29/2019
« Last Edit: April 27, 2021, 06:35:55 PM by reinhardtjh »
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karman1970

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Re: Digitrax Throttle Capacitors
« Reply #11 on: April 27, 2021, 07:03:12 PM »
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If Digitrax isn't helpful (and I'm not very hopeful based on other responses) then you should check at the Digitrax GroupsIO mailing list.  Others there have done self repairs on most of Digitrax's products.  It's probably in the archives somewhere that someone has replaced the caps on a DT300.  The DT300 was a most desired throttle by some as it sits right int he middle in functionality between the DT100 and the UT4.  I know of several on the list that used to go to far lengths to get more of the throttles.

Groups IO: https://groups.io/g/Digitrax-Users

I just did a search of messages for "DT300 cap" and there are quite a few.  One thread as old as 12/15/2000

One really specific thread is https://groups.io/g/Digitrax-Users/message/220241  It is recent, being posted 08/29/2019

Appreciate it.  I will check out those links.  Yeah, they responded and had nothing to offer that I hadn't already discovered myself.

mmagliaro

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Re: Digitrax Throttle Capacitors
« Reply #12 on: April 27, 2021, 07:13:17 PM »
+1
I think I would work it with little diagonal cutters and maybe even a Dremel, to cut the old caps apart and get them off the plastic bases, and then use the soldering iron to get the bits of leads and the base off.  You're going to probably have to do something like that to get the old ones out no matter what, as Peteski described.

But having done that, I would "swim against the tide" here, and just get some small electrolytics that are 4.7uF 25v,  with leads, and carefully solder the leads to the pads and glue or zip-tie the cap bodies somewhere convenient. Trying to get SMD devices soldered back in there with that difficult arrangement of the leads is a lot of unnecessary work and risk.

Point353

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Re: Digitrax Throttle Capacitors
« Reply #13 on: April 27, 2021, 11:18:39 PM »
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If Digitrax isn't helpful (and I'm not very hopeful based on other responses) then you should check at the Digitrax GroupsIO mailing list.  Others there have done self repairs on most of Digitrax's products.  It's probably in the archives somewhere that someone has replaced the caps on a DT300.  The DT300 was a most desired throttle by some as it sits right int he middle in functionality between the DT100 and the UT4.  I know of several on the list that used to go to far lengths to get more of the throttles.

Groups IO: https://groups.io/g/Digitrax-Users

I just did a search of messages for "DT300 cap" and there are quite a few.  One thread as old as 12/15/2000

One really specific thread is https://groups.io/g/Digitrax-Users/message/220241  It is recent, being posted 08/29/2019
Can you repost the information, here, for those that don't have a login for that group?

reinhardtjh

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Re: Digitrax Throttle Capacitors
« Reply #14 on: April 27, 2021, 11:28:47 PM »
+1
Can you repost the information, here, for those that don't have a login for that group?

Here you go.  But if you have Digitrax equipment, you really should join.  There is a lot of good information.

Quote
Claus Schlund \(HGM\)
08/29/19   #220241 

Hi List Members,
 
I recently acquired a DT300 throttle with the dreaded “Capacitor Plague” - this has been discussed on list in the past, and the DT300 throttles are known to be susceptible to this issue. You can read more on the larger topic of “Capacitor Plague” at the link below...
 
https://en.wikipedia.org/wiki/Capacitor_plague
 
The symptoms of this malady are that the DT300 alternately flashes between two displays, about once per second, first displaying the voltage and then a series of numbers, this alternating pattern of displays then repeats forever
 
The failed components are two surface mounted capacitors - they can be seen in the photo (linked below) of a factory throttle, they are the small round silver-colored components. One is above the chip marked "Microchip" and the other is below. These capacitors are inscribed with the letters "4.7 25G 003".
 
https://live.staticflickr.com/65535/48642360371_422c385092_o.jpg
 
After some research, I found these are (probably) 4.7 microfarad 25 volt capacitors.
 
I figured since the throttle was already unusable, I had nothing to lose in trying to fix it myself by replacing the failed capacitors. While such capacitors are readily available for purchase, I casually went and checked my stash of spare parts. I didn't find an exact match, but found two capacitors which were 10 microfarads. That means they have about twice the capacitance of the factory part - I did not know if this would still be ok or not, but I thought I would give them a try and see what result I got. Another difference was that the the factory capacitors are surface mount style, and the ones I had came with leads for thru-hole mounting.
 
By far the hardest part of this job is removing the old capacitors - this work is a bit tricky. The capacitors have two solder connections, and of course you can only really heat one side at a time with your soldering iron, right? I used a very fine-tip soldering iron, I heated one side of the old capacitor and used my fingernail to tilt the capacitor away from the soldering iron just a few degrees, thus raising that one side away from the printed circuit board. Don't over-do the tilt here, or else you might damage the copper traces on the printed citcuit board. I then did the same on the opposite side. Several iterations later, the capacitors came loose.
 
One of the two factory capacitors is right next to a plastic barrier that is part of the case - I carefully trimmed away the plastic in just that area so I could access the capacitor with the soldering iron.
 
Keep in mind that these are electrolytic capacitors and so they are polarity sensitive. The factory capacitors have a black band on the NEGATIVE side, and the replacement capacitors I used also had an indicator mark on the negative side.
 
I then put a bit of fresh solder on the (now vacant) solder pads where the old capacitors had been, then trimmed and solder coated the leads on the replacement capacitors. The final step was to hold the replacement capacitors in place, and to then heat the joint to reflow the solder and make the final connection.
 
You can see the end result in the image linked below - the upper replacement capacitor is black, the lower is blue, but both have the same capacitance. Even though they are larger than the factory capacitors they replaced, they still fit in the case just fine. The two failed capacitors are visible in the bottom of the image.
 
https://live.staticflickr.com/65535/48642007793_d49603e39d_o.jpg
 
I plugged the DT300 to a loconet plug and voila! It worked! It is now a functional throttle again.
 
I hope this helps others who might be in this same situation.
 
Claus Schlund
« Last Edit: April 27, 2021, 11:30:52 PM by reinhardtjh »
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