I have a printer which is several years old, maybe eight years old.
The printer is badged as DELL (it came with the PC), but was probably made by Lexmark, their ink cartidges fit it perfectly.
It does not have a lot of work to do, the odd page from a datasheet, customer invoices for my business, small stuff like that.
For a couple of months the printer had been mis behaving, part printing a page and then giving up, when it did print a page the job would not clear from the print queue on the PC and the only way to clear the print queue was to restart every thing.
For a number of years now the ink cartidges have been held in place with the aid of sticky tape due to the failure of a cheap plastic clip.
Time for a new printer I was thinking.
I had been experiencing some radio interference problem for a few weeks, I first noticed it on the medium wave band, there was some wideband noise creeping over a station which I like to listen to at night.
I had also inherited some amateur radio equipment from a long time friend of mine who died recently, tuning around on the 40 meter band...
... what the HELL is that noise all over the place!!!!
Having tried all the usual things for locating noisy switchmode power supplies, which this noise almost certainly was, I was convinced that it was not something within my house and that it was coming from outside somewhere.
Listening on the car radio, the noise dissappeared as soon as I drove away from my house. The problem must be with me somewhere, but where? I had tried everything. Hadn't I?
OK, do it all again, switch everything off while listening to the radio and watching the spectrum analyser (this noise was splattering crud at 170khz intervals all the way from DC to 20Mhz).
Finally switching off the supply to the bench where the printer was sat...
...silence!
The problem was the little SMPS module which plugs into the back of the printer.
So what could be wrong with this thing to make such a noise?
The printer still works, maybe.
Should I try and get a new power supply? Probably obsolete years ago.
Should I buy a new printer? Looks to be the favourite option, the printer can be iffy after all.
Can I fix it? The SMPS is a sealed module, needs a hacksaw to open the plastic case.
OK, it is bust, just cut it open and have a look, there is nothing to loose.
Inside nothing was obviously burnt or broken, there was one resistor which obviously runs warm, but otherwise nothing.
OK, lets try all the electrolytic capacitors, they all measure OK except one which measures 0uF rather than 15uF !!!
A trial replacement with a grossly oversized capacitor and the power supply is working, quietly, no vomiting all over the HF radio spectrum!
So, order up some new capacitors from RS* to replace all the electrolytics in the power supply, carefully close up the plastic case and seal the hacksaw cuts with epoxy.
Test.
Result, no radio noise and a printer which behaves itself.
No stopping part way through a page.
No stuck printer queues.
Success!!
So which capacitor was it that was open circuit?
It was the filter/reservoir capacitor on the input side of the SMPS, the capacitor which smooths the rectified mains which feeds the oscillator.
What surprises me most about all this is, how did the printer work at all?
That little SMPS did a valiant job of providing a DC supply to the printer when fed with rectified AC.
So JimB is well chuffed and the printer lives to churn out some more invoices, and JimB will be even more chuffed when the invoices get paid!
JimB
* for our readers in the USA, RS is "RS Components" a large supplier of good quality electronic parts, amongst other things. Not to be confused with Radio Shack.
The printer is badged as DELL (it came with the PC), but was probably made by Lexmark, their ink cartidges fit it perfectly.
It does not have a lot of work to do, the odd page from a datasheet, customer invoices for my business, small stuff like that.
For a couple of months the printer had been mis behaving, part printing a page and then giving up, when it did print a page the job would not clear from the print queue on the PC and the only way to clear the print queue was to restart every thing.
For a number of years now the ink cartidges have been held in place with the aid of sticky tape due to the failure of a cheap plastic clip.
Time for a new printer I was thinking.
I had been experiencing some radio interference problem for a few weeks, I first noticed it on the medium wave band, there was some wideband noise creeping over a station which I like to listen to at night.
I had also inherited some amateur radio equipment from a long time friend of mine who died recently, tuning around on the 40 meter band...
... what the HELL is that noise all over the place!!!!
Having tried all the usual things for locating noisy switchmode power supplies, which this noise almost certainly was, I was convinced that it was not something within my house and that it was coming from outside somewhere.
Listening on the car radio, the noise dissappeared as soon as I drove away from my house. The problem must be with me somewhere, but where? I had tried everything. Hadn't I?
OK, do it all again, switch everything off while listening to the radio and watching the spectrum analyser (this noise was splattering crud at 170khz intervals all the way from DC to 20Mhz).
Finally switching off the supply to the bench where the printer was sat...
...silence!
The problem was the little SMPS module which plugs into the back of the printer.
So what could be wrong with this thing to make such a noise?
The printer still works, maybe.
Should I try and get a new power supply? Probably obsolete years ago.
Should I buy a new printer? Looks to be the favourite option, the printer can be iffy after all.
Can I fix it? The SMPS is a sealed module, needs a hacksaw to open the plastic case.
OK, it is bust, just cut it open and have a look, there is nothing to loose.
Inside nothing was obviously burnt or broken, there was one resistor which obviously runs warm, but otherwise nothing.
OK, lets try all the electrolytic capacitors, they all measure OK except one which measures 0uF rather than 15uF !!!
A trial replacement with a grossly oversized capacitor and the power supply is working, quietly, no vomiting all over the HF radio spectrum!
So, order up some new capacitors from RS* to replace all the electrolytics in the power supply, carefully close up the plastic case and seal the hacksaw cuts with epoxy.
Test.
Result, no radio noise and a printer which behaves itself.
No stopping part way through a page.
No stuck printer queues.
Success!!
So which capacitor was it that was open circuit?
It was the filter/reservoir capacitor on the input side of the SMPS, the capacitor which smooths the rectified mains which feeds the oscillator.
What surprises me most about all this is, how did the printer work at all?
That little SMPS did a valiant job of providing a DC supply to the printer when fed with rectified AC.
So JimB is well chuffed and the printer lives to churn out some more invoices, and JimB will be even more chuffed when the invoices get paid!
JimB
* for our readers in the USA, RS is "RS Components" a large supplier of good quality electronic parts, amongst other things. Not to be confused with Radio Shack.