Electronic query

[Blagard]

Hi, I have an old epson printer (RX585) that failed to power up, just a single blink of the LED when trying.

So I took it to bits to get to the power supply unit and checked for output and it gave the 42V DC it should have. No sign of bulging caps or overheated components so put it back together thinking maybe the mainboard was dead. But for the hell of it tried turning it on and voila it came on! - Nothing had been changed. Printed test sheets OK to.

So I turned it off to put it back in its usual place but found it was back to the same no power up state. The same single blink from the power LED, nothing more. I have looked over the mainboard and could not see anything physically wrong looking. The power supply is still 42V as it should be, the only other circuit boards are on the back of the front panel where the on/off switch LCD and buttons are. Any ideas of what to try next?

While it gives the 42V it should from the power supply board, could it still be an issue?

I once had a PC with a similar start up problem and it was just bad caps on the motherboard and easily fixed. Unfortunately with no sign of any bad caps on this main board I am stumped.

I am wondering what electronics latch on to the power supply when it is turned on.

 

[bernardgreen]

It could be a solder joint that has gone dry and a minute bend of the PCB makes or breaks the connection. Sometimes the board is slightly bent by the fixing screws and unscrewing the PCB from the mounting can allow the board to straighten and the dry joint becomes conductive. Old plastic cases can distort and strain the PCB.

 

[Blagard]

Could be a joint, but in-situ the power supply is OK and it worked when re-assembled.

When plugged in the power supply is available 24/7 for the printer to power up, but where would the circuit be that latches onto the power when the power button is pressed?

Edit:
After really closely looking at the main board (using a jewellers loupe) and not finding anything that looks dodgy I have decided to replace the capacitors based on nothing more than they are a common source of problems on aged boards and cheap enough! You would have to half remove them to test them anyway. With the power supply being at the correct voltage I am going to leave that alone.

 

[nflowers]

You can download the service manual here https://yadi.sk/d/ygvmlCpAFkha4 (no idea who yadisk are or where they got it from!) The circuit diagrams are on the last few pages with the internal PSU circuit on page 130.

 

[Blagard]

Thanks, but I had already downloaded the full service manual before taking it all apart! - I used http://elektrotanya.com/epson_stylus_photo_rx585_595_610.pdf/download.html
That is where I got the voltage output for the power supply from.

 

[Sam Gangee]

The PSU voltage(s) should be measured under load. Also, measuring the PSU voltage(s) with anything other than an oscilloscope will not tell you the level of ripple. Aged capacitors will allow high-frequency spikes to appear on the "DC" output, which might interfere with the operation. The next step (in a properly equipped workshop) would be to measure the ESR of each capacitor with an ESR meter. (Cheap ones available via eBay but I don't know how good they are. I'd recommend the meter from Peak Electronics.)

As you don't have the equipment, you could take a risk and replace the capacitors but be sure to use low-ESR types in the critical positions, otherwise you'll be back to "square one" in a few months. If you don't know which are the critical positions, (usually 100uF and higher) then use low-ESR capacitors for all.

http://www.satcure.co.uk/accs/low_ESR_capacitors.htm

Note: I'm not convinced that the PSU is your fault cause. The most common cause of faults is the CONNECTOR - any sort of connector. If there are any leads with plugs, I'd squirt the contacts with WD-40 and work the plugs up and down a few times.

 

[Blagard]

Thanks Sam,

I was aware that I was not testing under load, and have read about the ripple issue which is why I thought having 42V was not in itself conclusive that the Power supply was OK. I have in fact ordered very low ESR capacitors as the end out cost is really nothing compared to the time to do the job, I also buy branded ones. Good point about the contacts, I will check that out before replacing anything. To date I have found capacitors have been the single most common failing component on things that I had that stopped working and came back to life with replacements. However I have been lucky as most showed clear signs of failing! It is because I was unable to identify the most likely cause of the problem that I posted to get some ideas on what else to look for. - I appreciate the positive response.

I have only ever used WD40 on external wires on my car as it is good for keeping moisture at bay (I keep a can in the boot of my 45 year old MG!). I'm not so sure about using it on electrical contacts other than lubricating the moving parts of switches, but I do have some contact cleaner that I suspect would be better suited.

Reading your link, I am also thinking of seeing if applying a little heat will allow the circuit to work again and provide confirmation of a sorts that a capacitor or two may be the culprit. - If it does I'll let you know!

 

[Sam Gangee]

I'm not so sure about using it on electrical contacts other than lubricating the moving parts of switches, but I do have some contact cleaner that I suspect would be better suited.

I've been using WD-40 for this since it first reached the UK shores from America. I've cured "noisy" potentiometers and various contact problems without causing any bad effects. In contrast, switch cleaner seems to be a degreaser, which is not always good for contacts. In my opinion (based on practical research) low-voltage contacts should be lubricated and that includes switches.
Here's a note about greasing contacts: http://www.glodark.com/silicone2.htm

 

[Blagard]

I thought it might be interesting to post back some findings.

Although I was planning to replace some capacitors in hope of replacing a defective one I decided to see if the printer would start up with certain parts not connected. I got lucky in so far as I have found the printer will start up when all but one particular cable is plugged in. Marked CN10 on the wiring diagram it is one of a pair of ribbon cables that goes to the print head, but the printer will simply just not turn on unless ribbon to CN10 is disconnected. I wondered if anyone would have a good idea of the reason why? I have done a partial copy of the main board wiring diagram and could put the whole on if needed.
CN10.pdf

 

[Sam Gangee]

I'd guess that there's a short-circuit in the print-head and this is being detected on the start-up check.
However, I would do an ESR check of the main smoothing capacitor(s) on the 3.3 volt rail.

 

[JBR]

Will it print?
If so, perhaps you've got lucky and bypassed the sensor that checks the chip in the cartridge, you know, the one that makes sure you've bought a genuine cartridge!
I suppose if it's an old printer it may be pre-sensor though, like mine.