Roland SJ-640 keeps blowing fuse

[marshalmoody]

Hey Guys long time reader of this forum and first time poster. Usually I'm able to find just what I'm looking for on this forum for any question i have but this one has me stumped.

My Roland has treated us very well for the past nine years but i think its age is beginning to show... Five days ago we replaced the Magenta head. Change went smoothly as possible. Fired it up and started printing. Worked beautifully, until two days ago when we lost "group B" in our test prints. So now we have no Magenta or Yellow. We checked the fuse for continuity and showed that the fuse blew. So we checked the heads (Magenta & Yellow) to see if they would fire on another group so we changed the ribbon cables to "group A" and they printed. So thinking that the ribbon cable was the culprit, we changed the cables and soldered in a new fuse and fired it up and it blew the fuse again.

Ribbon cable has continuity all the way through the cable, is there something else that I'm missing and could be the culprit? Figures that it would happen when we actually have things to print...

Thanks in advance guys,
Jeff

 

[MrSalumi]

So you swapped the ribbon cable to group A to your magenta/yellow heads and it worked for how long? I would have thought the group B ribbon cable as well but it could also be a head that is blowing the fuse. Either your new magenta head is bad (unlikely if its new) or your yellow head's resistance is off. Maybe due to the new head ??? I dont know.

I would check those cables again (even the new one) and then run some resistance tests on the heads.. Old Magenta VS New Magenta VS Yellow.

Keep us updated! Good luck!

 

[marshalmoody]

Will do thanks for the fast response!

 

[CS-SignSupply]

Could also be a blown transistor on the same board as the fuse.

 

[marshalmoody]

Okay guys so I pulled out the multi-meter and started probing the heads. Heads checked out ok and so I moved on to the transistor banks. Turns out that the "TR22" transistor was reading almost zero. I was able to track down a transistor and soldered it in on Saturday and my magenta and yellow came back! everything is printing great again! the only thing that worries me is that the Heat-sink where the new transistor is, its getting really warm where as the other banks are staying cool. Sounds like its pulling to much current but I'm not sure.

 

[MrSalumi]

Nice job! Way to avoid a $1000 bill. You might want to think about setting up an auxillary fan somewhere over the board. It really couldn't hurt anything, assuming its all clean and not pointed anywhere next to the heads. Marshall, how did you check the heads specifically?

 

[Compilla]

Great Job Marshall..
I'd like to know how did you check the transistors as well.

 

[Jack Knight1979]

Nice work. I've had to replace about six transistors on my printer. sj-745ex. Great machine though.

Make sure you place thermal paste on the back of the transistor that's touching the heat sink. Also, make sure all the allen screws are tight and secure to the sinks on all the remaining transistors.

 

[Papajo]

The transistors on the head boards are paired, meaning they are specially matched after the manufacturing process so that they have the exact same properties. You can see this as when you measure the transistors they all give you the exact same values. This wont be the case with a retail transistor even of the same type. You can find the exact same transistors on old blown head boards if you can find one. You may also want to check the chip resistors around the transistors on the solder side. There are four of them on each line of transistors, you just have to compare the values with the neighbour transistor lines.