[jarppa]

I've been planning to use Brother HS-70A EDM for some of my projects but I came up with a problem with edge and center detection. The machine was built year 2005 and it's operated only for 1k hours.

Fault description: The machine runs otherwise fine but the edge detection and centering does not function. The machine indicates a contact no matter what I try.

I cleaned the machine properly and it didn't solve the problem. After contacting the Brother sales in US I received a diagnostic procedure which indicated the problem is with electronics. According to the diagnostic procedure unplugging a certain cable should disconnect the mechanical parts (which might be grounded) from the measurement circuit.

The problem is difficult because the damaged electronic board is expensive. The repairs costs about 5000 euros and the board has already been replaced once. The edge detection and centering worked for a day after the card was replaced and then the same problem repeated. Manufacturer does not give any warranty for the replaced electronic cards and the reseller hasn't been very helpful in solving the problem.

I've taken some measurements of the machine with a scope and during the edge detection I can record a 50kHz +-10V signal from the upper cutting head. The signal disappears if the wire is in contact with a work piece. I've assumed this is the signal the machine uses for probing the edge. As there is a signal I'd guess the problem is with the measurement of this signal but I this is really guessing...

I also pulled out the damaged card from the machine and checked all the connections. This didn't solve the problem either. The only thing I noticed was that there were more than ten components added on top of the SMDs by hand soldering and by using hot-setting adhesive. They are close to the part of the PCB where the "edge detection cable" ends. This might lead to a conclusion that there has been some problems with electronics and the manufacturer has tried to solve the issues by adding some components afterwards.

If somebody has had similar problems with this machine and has been able to solve them in some way, I'd highly appreciate any comments which might lead to solving this problem. As I'm working at a university we are always a bit short of money and we cannot really afford another 5k repair for the machine especially if the problem is not solved.

Regards,
Jari

[kakofonixgr]

Hi,
I have the same problem.
Did you find a solution?

(Did you clean all the wire connections? I was thinking about its a dirty wire, which did not send the signal to the electric board).

[edmmachs]

I ran into a similar issue a while back on an older wire EDM (not a Brother, but the same principle applies). The fact that your edge detection worked briefly after replacing the board suggests the problem might not just be the board itself but something affecting it—possibly a grounding issue or signal interference.

A few things I’d check:

Grounding & Shielding – Make sure all grounding connections are solid, especially on the measurement circuit. A weak or floating ground can cause erratic edge detection.If there’s excessive electrical noise in your shop, shielding the probe cables might help.

Signal Integrity – Since you scoped a 50kHz signal at ±10V, but the machine always detects contact, it could be that the detection circuit isn’t reading the voltage drop correctly. If you have access to another EDM .) compare the waveforms of a working machine to see what’s different.

Board Component Check – The extra hand-soldered components on your PCB could mean the manufacturer was fixing a known issue. If you can identify what was added (resistors, capacitors, etc .), it might give clues about what’s failing. If you have a good electronics lab at your university, you could test whether those added components are still functioning correctly.

Wire Contamination & Contact Points – I know you already cleaned the machine, but check if the wire guide or contacts have oxidation or a thin layer of residue. Sometimes, even a small amount of contamination can affect conductivity.

If the repair cost is too high, another option is looking into second-hand replacement boards or even swapping out the machine if you keep running into these failures.