Another tube replacement-Epilog EXT 40-they are sending a Coherent Tube

[Larry Bratton]

Well guys, this will be my 4th tube since I have owned this machine. I think this is 6 years now. Fortunately this one is only 18 months old and so is in warranty. Strangely, the tube ceased firing after just running a file and starting a new one. Everything on the board was good, interlocks showed good on the board etc. but after trouble shooting with Brian at Epilog he declared it to be a dead tube. OK, only problem is that they are backordered on the Epilog tubes ( I was like #12 inline for one). So, in true Epilog fashion, Brian came up with an alternative, a Coherent tube. I have a job I need to get out the first of the week, so I agreed to take it. (same warranty etc.). I have read good and bad about Coherent, but nothing that was recent, most back 3 or 4 years. Does anyone have any input for me on this brand of tube? He said they used Coherent in some machines and the bracket would be different but they would supply it. I also asked about the fans I have and he said he would check and if they were different, he would send fans with it. (Value of dealing with a quality company, I say)
Under any circumstances, Kudus to Epilog for helping, however it turns out. I figure I can't be any worse off because as I said, this is the 4th tube, so my luck with the Epilog tubes hasn't been the greatest. Thanks for your input.

[Dave Sheldrake]

I've used some pretty big Coherent resonators Larry and they have always served me well. They run a tad hot for me but nothing to really worry about.

cheers

Dave

[Mike Null]

Larry

My 45 watt Trotec has a Coherent tube now in its 7th year.

[Michael Hunter]

9.75 years for mine

[Sotos Patistas]

I'm on my 7th year of a 35 watt Coherent Deos tube. It's getting weaker, but still firing. For now. Likely get it recharged in a month or so.

[Larry Bratton]

Thanks guys. Sounds like I may have better luck with this tube in lieu of the Epilog tubes??? I was wondering why this happened the way it did. Is it possible that there is something else that caused it to stop firing other than the tube being dead? Most times a tube dies in degrees and not all at once. Anyone? Rodne, Steve?

[matthew knott]

The problem is you cant be sure if the tube is really dead or not, there are raft of problems that could stop it firing, there's always a chance that a new tube will not fix the laser, if it does then you know it was the tube.
A tube a year is very unlucky (if luck is all it is) you need better diagnostics from epilog for each of the failures, I would want to know what the failure was each time, if its 4 different faults then you have just been extremely unlucky, if its the same thing then what was it and how is it caused. Is it running in a harsh environment, ie heat,dust,humidity,cold ? Is it maybe a faulty PSU that is taking out the tube, everyone on here could go on guessing all day, but thats all you are going to get. Ask Epilog is they have any records of the other tubes and what the failure mechanism was, they may not. I would put money on the fact they get perfectly functioning tubes returned but they would be unlikely to tell you this as a replacement has been issued and everything is working again. Standard service engineer (in all walks of life) practice goes something like this.

Machine breaks, Change part A, still not working, change part B, still not working, change part C, nope thats not it, change part D, Successes charge customer for parts A,B,C, & D . They wont take the time to see if it was say only part D, or maybe it was all 4, or maybe A & D etc

Hopefully its just bad luck and this new tube will run for years and years like other peoples on here and this will be an end of it, but what if its not?

[Dave Sheldrake]

Worse still Matt is a cascading problem,

Resonator no longer fires
New resonator fitted
New one doesn't fire
Swap PSU
New resonator still doesn't fire

The first PSU had a fault that killed the reso, the new reso that was fitted was killed by the same issue, the new PSU that was fitted was trying to fire an already dead new reso, sometimes it ends there...sometimes it keeps going when the new PSU was killed by the second damaged laser.

I remember a friend who has a laser supply company having a mid-size series machine arrive that didn't fire, after mucho mucking about it became a pet project to get it working. After changing every part of electrical equipment in the machine at least once it still didn't work (and cost a lot of parts).

I think if the correct high end test equipment isn't available working out what is faulty often ends up as a hopeful process of elimination like you say

An RF tube every 18 months average would suggest to me something else is going on, 1 RF tube dying in 300 hours use I have seen,2 you have to be pretty unlucky,3 I'd be thinking ummm what the hell? 4! the maths end up being some pretty big numbers of that happening without a secondary root cause.

cheers

Dave

[Larry Bratton]

Thanks for the replies, however, I don't have a warm fuzzy feeling about this situation. I am happy to hear the positive comments about the Coherent tubes, but I am nervous about the possibility of some other mysterious electronic issue causing the tube to shut down. All of the talk about resos and PSU's etc is above my paygrade. I just need the sucker to work. I brought up the subject of the sudden failure to Epilog and they said about 50% of tubes fail in this manner..all at once. They questioned me about the operating environment and possible overheating, not an issue because the room is air conditioned and I powered the machine up to check the fan unit and they all worked fine. Sooo,,the tube will be here on Monday, a Deos RT582 and we shall see.
Dave, three tubes before,(1) original one lasted almost 2 years (right before the warranty period expired *wink*) (2)the one we got as the warranty replacement which lasted over 2 years-didn't die outright, but seemed weak and so we bought a new one and (3) the replacement for that one that we had to buy and we got it in March of 2012 that has died a sudden death. So not quite as bad as every 18 months.

[Dave Sheldrake]

Hiya Larry,

Reso = Resonator = laser source / tube / unit
PSU = Power Supply Unit

While I'm not a big fan of RF(epilog tube units) units being used in light industrial / hobby machines they are usually very reliable, even cheaper low rent glass tubes can run 2 years, mid price tubes will often do 2 - 4 years and high price can do 6 years plus.

If we say even 1 in 10 RF tubes fail early (a harsh estimate it's probably closer to 1 in 50 or more) but at 1 in 10 suffering early failure the probability of independent failure of 4 tubes early is 1/10 x 1/10 x 1/10 x 1/10, so about 1 in 10,000 chance of it happening as an independent event. At 1 in 50 it's 1 in 6,250,000 chance of losing 4 successive tubes early as independent events with no external cause.

2 possible reasons:

Another component is causing it
Epilog tube quality control went downhill very quickly for quite a while (4 tubes from a batch suggest a BIG batch over that time or a problem went un-noticed for years) (pretty unlikely)

cheers

Dave

[Larry Bratton]

Well what made me raise my ears a bit was that they were backordered on the tubes. I was like #12 in line for an Epilog tube. Usually Epilog is next day on parts and I was rather surprised. Just seems like an unusual situation. Is there a rash of failures coming down or what. Maybe that is not an abnormal amount? dunno

[Larry Bratton]

Just to follow up with this thread. I got the new tube and was that the old tube had died. Installed this one and it works like a charm. Did have to re-locate a screw on the existing hanger bracket to accomodate the Coherent design, which is just a little bit different from the Epilog tubes. Otherwise un-eventful save for the usual pita alignment, but got that done and cut and engraved with it yesterday. Haven't had a chance to do any testing yet, but intend to see if my cutting ability is improved. I cut 1/8 yesterday at 12s-100p-2500f as usual.