What's new
What's new

My QT10 Is slowly dying. Power supply shutting down. Can anybody help?

mmurray70

Hot Rolled
Joined
Jan 11, 2003
Hi Guys, I have an old QT10 with T1 control in great shape with very low use despite its age. But lately its giving me a little trouble. I've struggled with this machine randomly shutting off occasionally for couple years now. Everything runs fine and then just totally shuts off like you hit the off button. Turn it back on and it fires right up again. Might do this few times a week. But lately it struggles to come back on. Sometimes need to hold the on button in for 4-5 seconds and then let it go. And seems to shut down little more often, especially first thing in the morning.

So ive done a lot of reading on this and it looks like if the power supply output is too high/low or if current is too high it shuts itself off to protect itself. Sounds like this is my trouble. I have checked all voltages and they are great. 99.5V coming in to power supply and the outputs are all exactly where they should be. I wonder if I have too much current shutting it down? Or maybe voltages are dropping intermittently See PDF Here Power supply.pdf - Google Drive

I found one thread on the other CNC forum (google: Need help with QT 10 w/ T1 control) where a guy had a similar problem and unplugged one board and it stayed running. Then found a shorted capacitor on that board. This might be hard for me since problem is intermittent. I had a close look at all the capacitors tonight and most look great, one had little bit of corrosion on end but measured fairly high resistance across it so probably isnt shorted. Ive heard others on here reccomending replacing ALL caps on old machines. Is it worth replacing all the caps anyway even though they look good? How do I know which ones to replace? Do all capacitors go downhill or is just the round electrolytic ones? Disk ones of to leave alone? How about the yellow one in the picture. Does that type break down too?

Anything else I can check?
 

Attachments

  • 20211027_235706.jpg
    20211027_235706.jpg
    102.2 KB · Views: 47
  • 20211027_235712.jpg
    20211027_235712.jpg
    103.3 KB · Views: 44
  • 20211027_235957.jpg
    20211027_235957.jpg
    106.4 KB · Views: 47
  • Untitled.jpg
    Untitled.jpg
    83.1 KB · Views: 48

GuntisK

Aluminum
Joined
Nov 26, 2017
Sometimes a culprit could be also one of those tantalum capacitors (small blue ones). They sometimes become shorted out with age, so check these with multimeter or ESR meter. Corroded, but good looking electrolyte caps, even those with high resistance- all should be replaced with new ones. It is not so expensive. Don't look for exactly the same type or brand- main thing here is capacitance value and their voltage. Yellow caps I think are polypropilene - these very rarely die in digital circuits.
 

mmurray70

Hot Rolled
Joined
Jan 11, 2003
So if I were to replace the caps, would you just recommend the big axial ones or are we talking every single one including the small blue ones? I could probably manage to change the big ones. Replacing all the small ones seems like a huge job, probably out of my league.

Seen some videos of guys using thermal cameras to find hot areas of circuit boards to pinpoint shorted caps or damaged components. Is that something that could be worthwhile in this case?

Machine is working away fine here today. Everything else on this machine works so well, and has very little wear, would love to get a little longer out of her. But seems like this problem is only getting worse.
 

mmurray70

Hot Rolled
Joined
Jan 11, 2003
Well guys it finally gave out completely. It was indeed the power supply. I learned a fair bit about these T1s this week. If any of the voltages disappear, or if any are over loaded the whole power supply will shut down and the machine completely dies just like you hit the off button.

My 1981 QT10U has a TDK PD10a power supply and within this power supply there are 2 separate supplys, one for 5v and +/-12v and a separate unit for 24v. In my case the 24v unit is dead. I found a bad solder joint on the output that was arcing, I repaired this but no luck, there must be other components damaged on the board. Probably got damaged from the bad connection. All the caps look perfect and none are shorted.

I have a electrical guy looking at it on monday but if we cant fix it is there any reason i cant use any kind of universal 24v power supply? Something like this maybe? Blocked

If I was to use a universal supply do I need to match current exactly to protect other components if they short? My supply is 24v and 3 amps. There are much more options for 100w (4.1a)supplys. Im worried the unit above might be little too cheap. This one seems like a nice unit but its 4.5 amps. Dont want to fry everything else if something shorts. Blocked

Anybody have any advice?

20211104_110026.jpg20211104_110015.jpg
 

mmurray70

Hot Rolled
Joined
Jan 11, 2003
Got some good news. Got the machine back up and running tonight! Found an electrical guy to look at the old power supply and he replaced a few caps and a 555 IC and its up and running again!

Also spoke with a Tech from TDK and they suggested it would be fine to use one of their universal power supplies such as the LS100-24 to replace this so I ordered one for a spair. Only cost about 35 USD.

Ended up being pretty cheap fix. Mitsubishi did have a direct replacement for the PD10A but cost was $7200 USD! Pretty crazy.
 

madmachinst

Stainless
Joined
Jan 15, 2007
Location
Central FL
Got some good news. Got the machine back up and running tonight! Found an electrical guy to look at the old power supply and he replaced a few caps and a 555 IC and its up and running again!

Also spoke with a Tech from TDK and they suggested it would be fine to use one of their universal power supplies such as the LS100-24 to replace this so I ordered one for a spair. Only cost about 35 USD.

Ended up being pretty cheap fix. Mitsubishi did have a direct replacement for the PD10A but cost was $7200 USD! Pretty crazy.

Thanks for sharing. U never know when this will come in useful. Where did you find the electrical guy? How much did repair cost?
 

mmurray70

Hot Rolled
Joined
Jan 11, 2003
Thanks for sharing. U never know when this will come in useful. Where did you find the electrical guy? How much did repair cost?

Was an electronics guys working at a university. He used to do some repairs for the last shop I worked at. He wanted $20 for the repair! I gave him $100 but he was very reluctant to take it. Not many people around like this anymore. Talk about one extreme to the other going from Mitsubishi to him!
 








 
Top