Problem with the 5 volt supply (Boss)

[creep_pea]

Hi

Every now and then when I switch my machine (Boss 6.1) on the computer side doesn't power up, the screen is totaly blank and no lights on. When this has happened I've checked the voltages as per the manual and found on each occasion the regulated 5v suppy to be near enough zero, then while I'm double checking everything else it just powers up and everything is back to normal/fully functional.

So is there anything I should be looking at, adjusting replacing or cleaning, that could cause this to happen?

I guess it must be something within the regulated power supply unit as the unregulated supply has always been fine.

Thanks

Chris

[zcases]

Chris - just noticed your power supply problem. I just gutted a Boss5, and in another couple months or so will be gutting another one. I just put a bunch of the parts on eBay (seller ID = zcases) after I didn't get any responce from the classifieds on CNCZone. Could be some good spare parts for your Boss.

[machintek]

There is a service bulletin that the fact that the BOSS boots on power up is only lucky. In theory the proper way to start up the machine is to "reset" the machine using the reset button.
I have found that this power supply has been very trouble free. But have you checked the regulator board for a bad connection or bad solder joint?
I have had a few machines drive me crazy where the machine would reboot for no reason. I have narrowed that down to the zener diode in the 5VDC circuit. It gets flaky and goes into conduction at random. I unsolder it and if the problem goes away, I know to replace it.

George

[creep_pea]

Thanks again

Zcases will have a look but I'm hoping I won't need anything, also I'm in the U.K. so it probably not worth the cost of postage but thanks anyway.

George there is evidence of trouble on the regulator board as someone before I got it has soldered a new chip in or re-soldered the original chip back in for some reason, you can see the heat discolouration on the board and the poor quality of the solder, all the joints look OK though just scruffy.

The zener diode you mention, is it on the regulator board or in the circiut shown below?

Cheers

Chris

[jsmith2170]

Hello Chris
I have 2 of these power supplies going for spares and i am in the UK.
1 is known to be good, the other can easily be checked.
Let me know if you want one. Based around manchester

[machintek]

The zener is between test point 7 and 8.

George

[creep_pea]

Hi

It started up fine the last few times so I'm going to leave it alone untill it goes again.

George thanks for that, thought it would be that one but wasn't sure if there where any on the regulator board, would the zener show up bad using a diode test between the test points.

Chris

[machintek]

A zener is a funny creature. It goes into conduction above its threshold voltage. It has been my experience that this one decays with age and conducts intermittantly causing the 5 VDC to drop and the machine to reboot. This can happen once a day, or multiple times a day. With these older BOSS machines it is real pain as you lose the program, TLOs, and zero position. All this must be reloaded. There is no way to monitor this event so the only way to verify that this zener indeed is the problem is to remove it from the circuit. This is not easy either as the entire white power supply is removed and opened and the zener removed from the circuit.

George

[creep_pea]

Thanks again George