Mercury II laser repair experience

[ensar dubravic]

Hello everyone,

I have been reading engraving forum posts for some time but never posted anythig until now.
Reason of my post if to sharethe experience with repair of my Mercury II 25W engraving machine, so it could be helpfull for someone.
Two weeks ago my brother managed (I discovered it later) to burn parallel port on laser machine. After instaling usb comunication my machine did not worked properly. After I send the file to engrave machine starts and after some engraving it stop with message „pcl command error“. I send the file again and it engrave the same graphics with out problems.
Some times no metter how many times I send the file it does not engrave it,
I tried everithing, new firmware, shorter usb cable, reseating memory, new driver. Even installed Explorrer firmware on Mercury II (it can not home itself since carriage hits end of work envelope because of larger work area in Explorer). Main board and integrated circuits are the same for several models.
So I took soldering iron from my secondary school „electronic geek“ days, my universal voltmeter and a little bit of electrical engineering knowlege I have.
Few screws, thaking a photo of all connections and main board is out.
Next to parallel port on main board is series of zener diodes which are overvoltage protection for rest of the circuit. I noticed two short circuits on two of those diodes. After taking them of I discovered that diodes are ok which meant that damage is further in circuit board. I followed pcb connections from those diodes and found that integrated circuit 74AHCT244D is damaged (there are several integrated circuits between parallel port input and FPGA chip, so probably some of those ICs will be damaged if overvoltage happens).
I just disconnected this IC and now laser works perfectly. Now I have time to find replacement IC.

The most important thing when dealing or reparing electrical circuits is DOUBLE check if power and cables are disconected, and if you never soldered any part of electrical circuit, semiconductor or similar it is better for profesional service.

[Mike Null]

Ensar

Welcome to Sawmill Creek. We look forward to your participation.

[Tony Lenkic]

Ensar - Welcome to SMC forum.

You have very good troubleshooting skills there I must add. Where are you, in Sarajevo?

[ensar dubravic]

I am from Tuzla. Some 120km north-east from Sarajevo.

[Tony Lenkic]

I remember Tuzla. Are you able to find that chip locally or you have to import it?

[ensar dubravic]

There are some simillar ICs that I can find here but probably will have to order from abroad.
You have been in Tuzla?

[Dan Hintz]

That's an octal buffer chip, high-speed CMOS with TTL-level signals. Should cost you less than $1 if you have any local shops, maybe as much as $50 if you have to mail order and the place has minimums and/or high shipping charges.

Wherever you get it, make sure you get the HCT version.

[Brad Knight]

I was in Tuzla about 15 years ago... didn't get the opportunity to see many sights though :(

[Tony Lenkic]

Ensar - No I have never been in Tuzla or in BiH just remember from geography lessons.

You should be able to get the chip either from Beograd, Zagreb or Ljubljana. In USA single piece order is only $0.63 from Digi-Key but question is will they ship one piece only. If you have hard time finding one let me know.

[ensar dubravic]

Thanks Tony, since the chip is very usual it should not be the poblem to find.
Dan is right since it is used for comunication with parallel port the chip has to be HCT version.
Interesting thing about the chip is that its input pins must not be left open with the rest of chip working, because in that case output starts to oscilate which causes problems in rest of the circuit. And that is exactly what happend in may case, those oscilations coused random problems. FPGA chip was comunicating with USB and at the same time it was receiving some signals from this damaged chip from parallel port section.

[Viktor Voroncov]

Very helpful story, Ensar :) I am remembering 1998 when I have start my relationships with GCC. On Mercury suddenly drop down power to 50%, :( we have sent report to GCC, they ask me send tube for repair, freight was about $800, repair another$1200. Customer didn't work 2 weeks - was very angry :( After some time same thing with same laser, but during second time laser was out of warranty. We decide at least TRY to fix problem by ourselves. When we have opened upper cover of tube we saw two identical circuit boards. On one board was broken (very good visible - burned) condensator. We just check type of condensator from good board, buy it from nearest shop for $1 and repair. Save $1999 on second repair :) From that time we did 90% of repairs inside company.