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View Full Version : Dead Synradf tube..gonna try surgery



Rodne Gold
11-07-2013, 6:53 AM
My synrad J48 died , way out of warranty (2006 tube) so we decided to open it . got a shock when I saw some components had desoldered themselves.on both the RF boards.
One resistor looks fried .
We gonna try repair by just checking the desoldered components and resoldering them.
Must have had a lot of heat - not sure why this happened , but the board and other stuff don't look damaged...
Here are some pics
a copy of the circuit diagram is to be found on PAGE 18 of this PDF

http://www.synrad.com/Manuals/j48v54.pdf

Dan Hintz
11-07-2013, 7:24 AM
Holy is that unbelievably poor design work...

EDIT 1: I doubt many others would have the same thought, but if that were me, Rodney, I'd seriously consider laying out a new set of RF boards that had proper pads/lands for the components on the board. Flying leads and deadbug assembly techniques should only be used for prototyping, not for production level work. It's so inexpensive to have a board manufactured, I can't believe Synrad wouldn't redo those after adding so many changes.

EDIT 2: I'd also carefully measure those component values while you have them out of the circuit, in case you need to replace anything in the future. If you don't have the ability to tune (as most here wouldn't), replacing with a near-exact value would prevent the need to do it.

Joe De Medeiros
11-07-2013, 9:08 AM
Holy is that unbelievably poor design work...

EDIT 1: I doubt many others would have the same thought, but if that were me, Rodney, I'd seriously consider laying out a new set of RF boards that had proper pads/lands for the components on the board. Flying leads and deadbug assembly techniques should only be used for prototyping, not for production level work. It's so inexpensive to have a board manufactured, I can't believe Synrad wouldn't redo those after adding so many changes.

EDIT 2: I'd also carefully measure those component values while you have them out of the circuit, in case you need to replace anything in the future. If you don't have the ability to tune (as most here wouldn't), replacing with a near-exact value would prevent the need to do it.

That was my first thought, having spend 20 years designing circuit boards for Ford.

Rodne Gold
11-07-2013, 1:05 PM
I think these are tuned board , tuned on the fly maybe , might that the reaon be they not so well constructed..must admit I was a little concerned to see component leads twisted and soldered.

Would the resistors that are fried be responsible for such heat that it desoldered components?
My problem is why did they fry? Its also a 309 ohm resistor , odd impedance , but they quote a 1% tolerance , so I recon a 310 should be ok...
The repair guys say they will solder the components back in place with the boards still mounted on the tube , I recon I would like to see the underside of the boards and inspect for damage.
Mailed synrad- but no reply yet

Dan Hintz
11-07-2013, 1:51 PM
Rodney,

I don't see any 1% resistors on the RF board (other than the 4-turn pot), just 5%... are you talking about a burnt component on the control board?

EDIT: LOL, nevermind, my mind skipped right over it.

I don't see anything special about the 309 ohm resistor... it's mainly there to limit current into the gate drive circuit.

Rodne Gold
11-12-2013, 7:42 AM
No luck , despite testing all the components on the board replacing damaged and testing the board (local electronics co)
Same issue , it's the tube but not the RF boards..worth a try tho.
No reply from synrad - mailed photovac for their comments or estimate.

Walt Langhans
11-12-2013, 9:36 AM
Very interesting thread :)

So is this a 'let's see if we can fix it because it's their' project, or are these tubes super expensive and you're trying to save it?

Rodne Gold
11-12-2013, 11:20 AM
Super expensive , new about $4500. Even to repair , with freight etc , it could easily cost me $2000+

Andrew Stow
11-12-2013, 2:27 PM
Related question:

How big of a deal is it to get set up to service your own lasers? Looks like you own quite a few. I mean as far as cleaning the tubes and recharging them.

As far as the electronics stuff goes, I recently had an issue with an epilog keyboard/LCD. Went through a song and dance for months trying to diagnose the issue and finally just bit the bullet and bought a refurbed one from Epilog. I feel like if I'd had the diagnostic tool that plugs into the diagnostics port on the board, I might have been able to figure it out and fix it. It wasn't like your case where at least something was obviously burned up.

In your case, it could also be that the component you're looking at fried because some other component failed, first.

Dan Hintz
11-12-2013, 4:48 PM
Keep us (me?) in the loop, Rodney... a "dead" tube isn't completely useless.

Rodne Gold
11-13-2013, 8:09 AM
Photovac have offered me an amazing deal if I send them some other dead RF tubes we have and cant use , along with the J48 , they responded instantly , Synrad has not bothered to reply to me.
Freight is going to be the problem , its expensive to send stuff from South Africa to USA so will have to work out the best way,
Its not really possible to set up a repair facilty here - we dont have the knowledge and the equipment , and im sure the equipment will cost 20x a laser tube cost...

Albert Nix
11-13-2013, 10:41 AM
Good thread...What's the wattage on the tube.

Rodne Gold
11-13-2013, 10:51 AM
25 watts J48-2 tube...