RCA DCM425 cable modem, dropping connection.
       17. Simple electronic devices.        

17.39 Cable modem RCA DCM425, problem & repair (dropping connection).

It's about RCA/Thomson cable modem, and how quickly repaired in the home.

If you have just such a modem, it is likely that you have, and I had such a problem. From time to time the modem loses the connection and left left you without the Internet. Technical support from service provider - helpless, as usual.

But one thing look mysterious. This modem has lost the connection to the ISP when there was rain, snow or temperature dropped sharply on the street.

The first thing you should do is to check what's going on the diagnostic page (for this modem at

As a result, we have the timing error, which does not allow the modem to synchronize. And most often it occurs in my side.

From this point you can begin to do something. First, the modem dropping connection when the temperature drops. OK. It's time to heat it with a hair dryer and see whether the connection is restored. If yes, then your modem has the same problem as mine - bad capacitors..

Open modem case and remove the board (under the rubber feet are four screws).
All assembled on a single printed circuit board.

Two input capacitor change immediately, even if they do not look bad. This will prevent you from headaches in the future.

If you have tools that would check the frequency of the two resonators, then do it. If not, skip it.

In my case, both were working at 15.995 MHz and 23.993 MHz.

Further, my scope showed that the voltage of 3.3 volts is not very stable (at the "minus" of this diode).

The cause was found in bad capacitor (manuf. «G-LUXON»). It is marked on the next photo.

You can stop here. Replace the last cup (470uF to 1000uF), power up modem and it will work, as good as new.

Given that 3 of 6 capacitors were bad and we never heard of
«G-LUXON», all electrolytic capacitors is better to change to something better known. I have the "donor" with capacitors "SANYO".

All capacitors that I changed, are marked on the picture (the final values and voltage of cups).

If you are using power supply with transformer & rectifier, the input capacitors (those 1600u16V) must be rated for the voltage of 25 volts (1000u 25V). If stabilized 9-12 V, then on 16 volts will be enough (1000u 16V), or as on the photo.

Turn it on and enjoy, even on the middle of the night.

If all went well, do not forget to cancel the appointment with a technician from the cable company :)

Dec. 30, 2016  SKootS


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