Very very nice control box you've got there! Mine is not as nice but I have much bigger problems right now  

My Synrad made the worst kind of smoke. Looks like I could repair it but it would be nice to know why this happened in the first place.

Edit: A service manual would be good and schematics over the RF board. Synrad have not answered yet.

Ohh dear. 

With a bit of luck it is just the 1000pF silver mica which has expired.

Here is the RF board schematic (assuming you have the version with just one single RF output transistor).

Tweakie.

Yeah I sure hope so. Thanks for the schematic. What voltage do you have? I have 30VDC.

The same here, regulated 30 Volt, 14 Amp (made in China).

Tweakie.

(Observe caution with the riser from the tube, this is in a gas seal and has to be treated with respect when un-soldering / re-soldering the cap. Also all the conductive carbon / metal deposit (from the arcing) has to be removed from all the insulated areas of the circuit board if repairing).

Thanks for the advices.

I'll start with the caps. I've got two of them, one one each RF board.

OK I have two different RF boards. One has the MRF150 transistor, the other one MRF151.. I wonder if they have different MICA caps then. The blown one is quite unreadable..

Do you have a problem with both RF boards ?

I am no expert here but I understand that it is quite common for one RF board to fail and the laser to continue to operate on reduced power. So far I have seen two Type 48's which have had just one RF board replaced at some time or another during their lifetime.
The MRF151 is a slightly higher gain than the MRF150 but they are essentially the same component. The mica caps will be the same value on both boards.
I am uncertain about the setting up / matching but if it is adjusted at the threshold then lasing will begin at a pulse width of 3uS +/- 0.5uS at 5kHz PRF.

Tweakie.

Thank you! Sorry for posting here in your thread without asking. Your name was the first to pop up in my head when the laser broke.
I'm on a mission to gather all the knowledge about repairing the synrads yourself

Someone said that you could tune this boards with an oscilloscope. I'm just guessing but I think you want the boards to be in sync?

No problem using this thread - this forum is all about sharing knowledge (it is slightly Mach related so I think we can get away with it  )

As far as I can see, there are two issues regarding setting up.

1) Matching, where the power output of each board is the same and adjusted with R3 (see earlier posting).
2) Tuning, where the RF frequency of each board is the same and adjusted with C5.

An oscilloscope, preferably dual trace, would be ideal when adjusting the frequency to match both boards. I don't think Synrad specify the exact frequency although it is probably around 30Mhz so you will have to measure the good board and adjust the repaired board to match it.
Take care when making any adjustments (use non ferrous, insulated tools) as high power RF is dangerous stuff to mess with.

Tweakie.

Well the situation is that there is no lasing at all so I guess both boards are dead. Or There is something stopping the second one when the first one is dead. Hopefully I don't burn my Fluke.