This is something that I’ve had happening blowing 2 – 100A input fuses out of 3 at least once every summer during the last 4 years and/or occasionally turning LED 2 on early in the morning when machine is first turned on the rest of the year. This LED 2 alarm doesn’t happen once the machine has warmed up to operating temperature.

It happens that I’ve read postings in this forum about this issue saying that it’s caused by some hybrid ICs in the SCR firing section which have to be warmed up prior to running the machine. By the way, the LED2 alarm happens while the machine is idle waiting until it’s at running temperature. According to a few pages I once got from Fanuc World, if LED 2turns on, one has to jumper CH16 to 0V. If LED 2 goes out, the problem is a field loss, if it stays on, it’s an overcurrent problem, which is my case. See attached pdf file.

Anyway, the machine could run most of the time until about 4 weeks ago it stopped and the Spindle board turned on LED 4. This is something I had never seen before. Apparently, the Spindle motor temperature sensor was activated but it was not. The LED 4 turned on as soon as I flipped the circuit breaker on, so something else was going on there. I removed the Spindle PCB from the machine and as I had no schematics whatsoever, I decided to see what caused LED 4 to come on in the first place. Soon I realized that the cathode of LED 4 was wired to M5 pin 1 which was shorted to ground. I kept looking and found that M7, M6 and M1 were also shorted to ground. MX designation for this board is for TTL ICs, a bunch of NAND and NOR gates.

A damage of this magnitude was not something that just occurred randomly as this board had survived more than 30 years without a problem. After several hours of reverse engineering this board, I found that the“fuse-blown” section of the Alarm fuses was connected to M7 IC pin 4. Checking the alarm fuse corresponding to F1, it was blown inside and it looked as if the 1.3A fuse arced inside the cartridge which also arced with the DC section that goes to M7. This arcing in turn took with it the rest of the ICs mentioned above. After replacing these ICs and clearing the shorts, I decided to put the Spindle board back into the machine and turned it on after having replaced F1 as well. When turning the machine on, LED4 stayed off, which was a good sign.

Then I had the operator test the spindle (after the mandatory one hour warm up time) by running it forward at 500 rpm, but the spindle did nothing. No lights on, no nothing, then I decided to continue to reverse engineer the board until I found what caused it to not run when commanded to do so. After some more hours, I followed the CN1 connector signals until I found where they went. Soon I found that control signals go into some square black ICs (A-RV03) that seem to level shift the signals from 0 – 24V down to 0– 5V for TTL logic. As the operator tried to run the spindle forward, I decided to re-install the PCB back to see with an oscilloscope how the signal behaved. Soon I noticed that the SFR signal (Spindle FoRward) went from 24V down to 0V and the output went from 4V to 4.5V which didn’t cause the spindle to run. I asked the operator to run the spindle in reverse and this time the spindle ran. This proved that as the SFR signal was active when the arcing occurred, the (HY4-IC) A-RV03 line corresponding to this signal was blown. In order to test for the rest of the circuitry related to SFR, I removed the jumpers that deal with spindle rotation on CN9 and rewired the pins so as to make the spindle run forward when commanded to run in reverse. Sure enough, it ran forward. This meant that only the HY4 IC was bad.

As I had found a couple of years ago that user jolulank mentioned something similar (the blown fuses thing), I asked him where he got the A-OS04s and A-OS03s ICs he said had been replaced in his machine and he said they couldn’t easily be found. The only option was to buy a junked board and pull out ICs as they were needed. So, we did, we bought a junked PCB for the parts. This time, however, the bad part was an A-RV03 which was recovered from this spare board and installed back into the original PCB. Unit was tested and Spindle ran in both directions. Now we could go back to original problem.

LED 2 and/or blown Fuses:

Jerry Shorter posted the following regarding fuses blowing:

https://www.cnczone.com/forums/fanuc/95354-input-fuses-blowing-6t-spindle-drive-2.html

HRH replied: “You possibly need a technical person who knows the drive and can check the firing and current signals with an oscilloscope.”

jdeere replied: “How is the accl/deccl is it rough, to aggressive?
Does it run smooth at commanded speed?
Possibly if either hybrid chip on the pcb replaced or the dither adjusted.”

In another posting, Jolulank asked about the same in his Fanuc 5T:

https://www.cnczone.com/forums/archive/index.php/t-113496.html

AI_The_Man replied: “Quite possible the firing board is causing the problem.”

Tmbruno28 replied: “firing problems can be check as follows:

Check in CH17(a, b, c) with an oscilloscope. If wrong exchange AOS04.
Check inCH18 (a, b, c) if wrong, exchange AOS03.
If problem occurs not at each time, first exchange AOS03.”

Armed with all this and Fanuc DC Spindle Maintenance Manual B-51649E/05, I checked the adjustments and found at CH17 a, b, c (synchronous pulse balance) that all three signals were about right per the manual while spindle was stopped. At 60Hz, the pulse widths measured about 1msec. Manual recommended between 0.8msec to 1msec.

However, measuring at CH18 a, b, c (dither shift circuit balance), all three showed 2.7msec pulse width while the manual recommends 1.4msec. See attached photo.

It was at this time when I called a CNC man based in North or South Carolina who told me that he could fix my Spindle board if I wanted, but to never touch the adjustments otherwise the repair would be more time consuming and expensive.

This made me hesitate, however, reading all the postings about this Spindle control made me wonder whether adjusting the settings could cure my problem. The CNC man mentioned, however, that 9 out of 10 Spindle boards with same symptoms have problems with Power Supplies. The only issues, so far, that I’ve seen are that +15V supply varies from +14.90V when cold down to +14.86V when warm, and the +24V supply varies between +23.65V to +24.75V either cold or warm, and shows more than 1V ripple voltage. The other supplies don’t show noticeable ripple voltage.

Another thing, the posting made by Tmbruno28 made me think, what did he mean by “if wrong” replace AOS04 or AOS03? In the case of “dither shift circuit balance” should I change all three AOS03s? Are adjustments correct at 2.7msec or should I adjust them down to 1.4msec if possible? All three settings a, b, and c have practically same pulse width.

If anybody has experience with these issues, please let me know whether I should either adjust or replace ICs. Also, if anybody can share or sell the schematics for this Spindle board I would really appreciate it.

Rafael