Determining SMD fuse value for Epson Stylus SX515W Printer Mainboard repair

Thread Starter

Marcus2012

Joined Feb 22, 2015
390
HI everyone, hope you are all well.


I’ve had a bit of an issue with my printer repair and I was hoping someone would be able to offer me some advice please. A leak in the printhead shorted the cable and blew a PCB SMD non-resettable fuse. The fuse is in series with the BJTs that presumably power the printhead. The printer works, firmware works, just doesn’t register cartridges and the CSIC is fine. So, I’ve moved the fuse off-board for easy access should I need to do this again and am using 20x5mm fuses. However, I do not know the value of the fuse. Epson are no help; they don’t know apparently. Is there any way I can determine the value at all? Or is it a case of trial and error going from low to high? The printer is old but a workhorse so would be nice to fix as I got a replacement printhead cheap. It’s an Epson Stylus SX515W which uses a CA48 Mainboard and the designation is F1, the only fuse present. I’ve attached some pictures. I’ve searched but cannot find a value for this. BJTs are unmarked so they don't help. The fuse measured approximately 1.56x0.75x0.45mm, LxWxD. Working back from this size seems to be up to 6 Amps which is way too much. I can’t imagine it being over 2 Amps. Can anyone over any advice as to how I should approach this problem? Any and all help would be appreciated. Thanks all in advance.
 

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Alec_t

Joined Sep 17, 2013
11,744
Or is it a case of trial and error going from low to high?
I reckon so, if you can't get the info on the fuse rating.
The manual indicates rated power consumption is 16W (in copy mode) or less, so if you know the voltage on that CA48 main board you can calculate the fuse value needed.
 

Thread Starter

Marcus2012

Joined Feb 22, 2015
390
I reckon so, if you can't get the info on the fuse rating.
The manual indicates rated power consumption is 16W (in copy mode) or less, so if you know the voltage on that CA48 main board you can calculate the fuse value needed.
Hi Alec, thanks for the reply. I thought that may be the case but I'm just unsure how low to start. I know that the FFC is only rated for 60V and 2 Amps so that's a start but I imagine it is lower than this, maybe 48V. I didn't think at all about looking at the AC power consumption, thanks for pointing that out. If I assume the 48V maximum then that would be 333mA DC the device is using while copying. This does seem a little low (maybe due to my naivety) to run the scanner and printhead simultaneously. However, this may be too high as I've noticed the parallel capacitor is only rated for 50V. And also, that voltage seems a little high for the logic components on the board, maybe it has multiple voltage rails from the PSU. I'm tempted to probe the terminals but I'm just so paranoid about creating another short and killing my mainboard. I shall try to research some more to try and identify voltage of other components.
 

Thread Starter

Marcus2012

Joined Feb 22, 2015
390
So, after some testing the PSU supplies 2x 42V rails and 1x Ground rail. One of the 42V PSU pins has continuity with the fuse and the NPN collector placing them in parallel. The fuse then passes current to only 2 pins on the FFCs which I am assume are the Vcc for the printhead and the CSIC model. The NPN and PNP seem to be in a push-pull configuration with a lot of the pins on the printhead making then capable of pulling them to low or high. Weird how the NPN is high side though. I assume the BJTs are passing most of the current when the printhead is in operation.

While the fuse has continuity with the 42V PSU input, when the unit enters standby mode when I plug it in it only displays a potential of 2.5V between the fuse and ground. This has confused me as it had direct continuity (2Ω) with what I measured as 42V (no load). Should I power the unit on entirely or is that a bit of a risk?
 

Thread Starter

Marcus2012

Joined Feb 22, 2015
390
Your call. If the fuse has already blown then presumably not much current can flow?
Good point :) I made the call and powered it up, firmware was fine, just prompted errors as expected and the voltage at the fuse rose to 42V. Seems like a lot but it is what it is. If it uses 16W when copying that would make current draw for the entire unit approx. 381mA @ 42V. Seems small but that is quite a lot of potential I suppose. This makes me think the fuse is a very small value. Possibly 630mA?
 

Alec_t

Joined Sep 17, 2013
11,744
So now you have to find out what downstream component(s) could draw more than xmA in failure mode to cause the fuse to blow.
 

Thread Starter

Marcus2012

Joined Feb 22, 2015
390
It's the printhead. Made a buzzing sound when it started up and then didn't recognise cartridges. It has ink on its internal PCB and some on the FFC. I've got a new printhead but I have no idea what current it draws, the only thread I found that directed me to the fuse suggests a "100 Ohm planar fuse" as replacement. I assume they meant resistor? If I were to use a fuse equivalent of the current limited by that resistor it would be about 420mA.
 
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