Synrad 48-2 Problem

[isak nordell]

Hi members. I found this forum when my laser stopped working few days ago.
From what I understand after reading some posts here it's the RF boards that are broken.
I bought this Synrad from a guy in Germany who said it was like new and gave me 6 months warranty. Now I can't reach him so that's probably BS..

Anyhow I'm glad I found you guys. Seems like some of you actually repaired your Synrads yourself. I've contacted Synrad describing the problem yesterday and are still waiting for some feedback.

I think both my RF boards are dead. I have an OEM J48-2.
First I lost half the power and then all. The green and red LED are working/responding as normal. I've checked the PSU (30.1V), tickle pulse and PWM and it looks good. I can even hear the noise when turning on the PWM. But no lasing.

On the Control board I have it says 01 rev. A

P1010001.jpg

The other boards capacitor have some minor discoloration but I'm not 100% sure it's gone. But my guess.. it's dead to.

Would really appreciate any input from you.

Best Regards
Isak Nordell
Sweden

[Dan Hintz]

Those boards are definitely toasted... that huge black spot was a component letting the smoke out. The voltage worries me, as well, but I'm not nearly as sure on that one... I thought those supplies were supposed to be 32V, but others will confirm/deny.

[isak nordell]

Well the manual says 30VDC. The guy who sold it to me said 29-32V. I guess I have to change those caps. Everything else looks good so far.

BTW. Anyone have the schematics on the RF boards?

[Rodne Gold]

It's not quite as simple as replacing components to repair the laser , the RF boards are supposed to be tuned , but having said that, I do know of folk who have just replaced the blown components and their laser has seemd to work ok , barring the fact that the boards seem to blow every 6 months or so..
Synrad will send you the tuning procedure , requires an off board controller and an oscilliscope

[isak nordell]

Yeah thats kind of what I've read before. Anyone have this tuning procedure? Synrad have not answered back.

I'll guess trying just changing the mica cap is OK. I'm not using this mashine more than 1hour/day so hopefully it lasts longer than a week.

[isak nordell]

Got in contact with Synrad. I'll keep you updated.

[Richard Rumancik]

Those boards are definitely toasted... that huge black spot was a component letting the smoke out. The voltage worries me, as well, but I'm not nearly as sure on that one... I thought those supplies were supposed to be 32V, but others will confirm/deny.

The current 48 series spec says 30 volts. However, the input voltage must be set to whatever voltage was used during "tuning" of the tube. Apparently you can tune at voltages between 30 V and 32 V. But if tuned at 32V and operated at 30 you can damage it, and vice versa. Usually there is a label on the outside of the tube indicating the tuning voltage. Unfortunately some tubes were just marked 30-32V which gave people the idea the voltage does not matter within the range. But it does, and can cause the RF boards to blow if incorrect. The problem is that if you get a used laser, you might not know what tuning voltage was used.

I think GCC for one was (still is?) using Synrad 48s tuned to 32V. Way back, they were using 30V OEM tubes at 32V but this was not a good idea. (Ask me how I know.) But I believe off the shelf 48s are currently set at 30V.

[isak nordell]

I guess the tubes loose their tuning after some years when capacitors gets old/change values (meaning that 30V might have been the right voltage for this tube, but no longer). Going to change to new caps and then re-tune the tube. The caps that blow were more than 10 years old..

[Richard Rumancik]

The caps seems to have been a problem for Synrad right from day 1. They beefed up the design along the way, with a better cap, partly to offset the fact that many tubes were being operated at the wrong voltage. This caused the caps to blow; since they couldn't prevent people from misusing the tubes (causing warranty issues) they changed to a cap that was less susceptible to damage. To be fair to the users, the early operating specs were not clear. You likely have one of the earlier designs. I think they changed the cap in 2002-2003 timeframe but am not sure exactly.

I am not saying improper input voltage is the only reason the caps will blow, but it just makes things worse. I don't know if the 2003 cap design change fixed it for good or not.

I assume you have the schematic from Synrad. If you don't let me know.

[Richard Rumancik]

Isak, here are a couple old links of a member who had the same problem. You might want to skim them for tidbits of info:

http://www.sawmillcreek.org/showthre...ORTED!!-WOOHOO!
http://www.sawmillcreek.org/showthre...ffed-confirmed

I found a "J" version of the 48 series tube Op & Service Manual at
http://www.kingyukg.com/Download%20f...ors_Manual.pdf

This is dated 1999. I will PM a "G" version OP & Service manual (1996 era) as I am not sure which one is closer to what you have. I don't have anything in-between. The current tubes Synrad sells are called "L" version. There is an RF board schematic inside. I'll see if I have anything else in my file.

[isak nordell]

Very helpful! Thanks a lot.
I changed the caps and it is now lasing with both boards! I have not tuned it yet and I wonder if it is a good idea. They were probably proper tuned and if changing a cap don't disturb the tuning then I'm good for now I guess. I'm not going to go above ~80% for now if I don't have to. Offer some speed for peace of mind maybe

But if the new caps go again I'll do everything from scratch with tuning.

Thanks again!

[Richard Rumancik]

Glad to hear you got it running. Changing the caps themselves will affect the tuning, but it depends on how much different the replacements were from the originals. As you know caps can have a large tolerance. I don't have the tuning procedure myself nor the equipment to do it - but on the RF board schematic C5 is marked "tuning" 15-150 pF. So I'll guess that tweaking that device is one part of the tuning procedure. From my recollection if you don't tune, it will put more stress on the caps you just replaced. So keep some spares handy just in case.

[isak nordell]

Here are some more pictures. There is no picture of the µC board but if says something like 01-rev.A So I guess that one is 2001.

P1010004.jpgP1010003.jpgP1010007.jpgP1010005.jpg