I run a pc200lc-6 excavator. The primary power relay next to the batteries will not disengage and the starter will not engage with the key switch. Starts fine with a screwdriver shorting across the starter solenoid. After the key switch is shut off, this relay continues to hold 3-5 volts and will not disengage the solenoid. I've had a very frustrating day of troubleshooting the culprit. I have narrowed down the problem to the $600 rebuilt alternator. When the R wire is disconnected, the power relay disengages. I have checked every other diode, sensor and possible connector associated with this part of the electrical schematic and the alternator is the guilty party. WHY????:beatsme Other major problems with this machine are the monitor panel and the engine governor control. The governor control was fixed yesterday. Turns out the bearings were getting sticky and for $15, 2 new bearings were installed. Cheapest fix I've done on this in a while. Of course these were not Komatsu bearings, not at that price! The symptoms were wandering rpms, dropped engine speed to low idle when travelling, rpm fluctuations during normal operations and excessive fuel usage. Over the years, the monitor has become increasingly darker. I used to turn on the lights to read it easier but now it is so dark that no amount of back light or fore light helps to read the display. At one time, the batteries where left disconnected for over a week and the monitor looked like new for about 1/2 a day until it had been powered up for a while. It is so dark now that I can not get the error codes to diagnose the situation. Also, the engine controller box led flashes while the pump controller led remains at a constant glow. I don't know which is right or wrong. Any suggestions would be appreciated. Are there any places to find alternator parts for a Komatsu at a reasonable cost? Is there any way to rebuild the control panel or too delete the black stain? Any ideas on what would cause the screen to get so dark over the years? Why does the alternator back bleed 4 volts to the main power relay? Should either the pump or engine control box LED flash or remain steady? Well, no amount of beer is going to fix this situation!:drinkup I like my Komatsu but I hate the price of their parts. The only things they sell at a reasonable price are filters. $300 starter solenoids, $600 alternators, $300 water pumps, man what a headache:Banghead
treemuncher, sounds like the LCD in your monitor is failing. I have known it before and exposure to prolonged heat and sunlight will cause rapid deterioration once it starts... how many hours on it? The monitor is a sealed unit and parts were not available over the shelf last time I checked. Find someone at your dealer to check if there is an exchange available or if there is any other option because as you indicated the monitor is crucial to troubleshooting. It would be useful to know what model and serial number the machine is because there were some major changes, different engine and later ones used one pump/engine controller instead of separate pump and engine controllers which is not clear on your post (at least to me) On some of them there is a small resistor between the R terminal and the B terminal which could give the symptoms you describe so make sure you have the correct schematic for the machine.
Treemuncher, You have diagnosed the alternator problem correctly. The system is in place to prevent engaging the starter while the engine is running. You will also find that when you first turn on the key switch that the oil pressure alarm will sound. The monitor system uses that same terminal to sense when the engine is running. With current coming through that terninal the computer thinks the engine is running but sees there is no oil pressure signal. That alternator can be fixed by a good repair shop. You do have to let them know what the problem is and explain why it has to be right. Most shops will put the unit on the test bench and see it producing voltage and stop right there. Basically you have a diode bleeding through. Most of my customers disconnected the R terminal and taped up the wire. That fix doesn't last long though because the diode will burn through in short order and you have to fix or replace the alternator anyway. Wulf is correct about later machines having a different cause. They used twin diodes instead and never told anyone what was going on. The diodes are located in the back right corner of the cab tied to the harness. The display problem is not repairable. Komatsu has been taking hits on it for years and I had customers quit buying them because of it. Wulf is correct in stating the problem is heat and sunlight. The story I got was that the material in the LCDs is burning out as a result of ultraviolit light. There is no fix for it but to replace the panel. There was a field fix that supplied a clear cover plate that protected the display before it burned out but I haven't seen them in a few years. You might try asking your dealer but most will just give you a dumb look. The Sumitomo brand machines had the same problem for awhile. The panel comes out by removing the four screws in the back and you will find the part number for that unit on the back. Make sure you tell the dealer you want the updated replacement.
Thanks for the input Thanks for the replies, guys. This is what makes these forums work so well! My serial number is A80880. The machine has just over 7k hours on it. Separate engine and pump control modules. It is an early version of the 6 series machine. My monitor has the swing priority mode. ( a useless option to me) When I had the alternator out yesterday, we checked all of the diodes inside the unit. I had also checked every diode on the schematic that was associated to the alternator power and starter circuit. All but one of these diodes were located behind the seat and the other was in the wiring harness near the monitor panel. Every diode checked as good with either of the two meters we were using. The alternator diodes also registered as good. I do not remember a resistor in the back of the alternator. I am guessing that it may be the voltage regulator that could be bad, but that is a guess as I am not an electronics major. I found this electronics repair site during a google search on the web last night. http://www.acsindustrial.com/mfrs/komatsu.php I will call them Monday and see if they can repair my monitor. If that is so, I will post it here on the board so that others may benefit from component's fatality. I'm just not ready to shell out $2500 for a new screen that I basically use for temperature and fuel level.