[SOLVED] Doerr DE300B / Falcon Eyes DE300B Studio Strobe repair

[decsystem20]

Greetings everyone,

I hope you can help me solving a problem that I can't solve by myself.
I'm not a professional repairman but I like to fix broken appliances given to me by my friends and colleagues (Hey! I know you know electronics...can you fix THIS?  )

The things I've fixed successfully so far are battery chargers (RC-Car-Racing stuff), SMPSs (mostly in TVs and PCs), some Electronic instruments (Synthesizers and Samplers from the 80s and early 90s, mostly powersupply issues )

Now I was asked to look after a broken Studio Strobe. I cant't identify the problem but have tried some things...all without luck.
It would be very nice if someone could put me in the right direction to bring the unit back to a working order.
I know mains voltage stuff with large capacitors is quite dangerous, but if I had done something seriously wrong I would not be able to post my problems here.   

Here is a description of what I've done so far.
Attached are some photos of the PCBs. The wiring inside is quite messy.

If I need to provide additional information, please tell me what is needed.

The unit is a Doerr DE300B, 300 Ws. I think it's from around 2009. It seems it is also marketed as Falcon Eyes DE-300B
 
-   When I got the unit the guy who was using it told me it trips the Studio RCD when the unit is triggered (regardless if triggered over sync or with the test button)
-   It tripped the RCD when hitting the test button
-   No flash, no “tick” on triggering
-   On some occasions the RCD was tripped when the unit was switched on
-   The trigger transformer was defective
-   With the trigger transformer removed the RCD was not tripped when the unit was switched on
-   After replacing the trigger transformer the unit still trips the RCD, sometimes when switched on sometimes on the first trigger sometimes on the second or third trigger
-   A “tick” is heard when the unit is triggered
-   When the flash tube is removed the unit can be switched on without tripping the RCD
-   If the PE is disconected in the unit, the RCD does not trip, a “tick” is heard but there is no flash
-   The RCD is still tripped if the TRIAC in the trigger circuit is removed


-   The tube was tested in another unit and produces a flash (In this unit the lowest setting sets the voltage to ~150V)
-   The voltage on the capacitors is ~170V on the lowest setting and ~320V on the highest setting
-   The Triac in the trigger circuit was replaced

-   How can I determine if the trigger transformer is of the right type? All transformers and datasheets I found look the same (resistance/pinout/pulse waveform)

-   The measured resistance values of the trigger transformers appear to be the same (of the replacement one and the one in the test unit, which is of a different make)


Thanks in advance for your time and help!

Regards,

Jens

[BreakingOhmsLaw]

Well, could be a hard one.
Let's start:
First of all, you should connect the unit via a isolating transformer, as mains-driven high voltage isn't something to mess with.
Also, if you have an adjustable one, you can run it at reduced voltage and see how the unit behaves when fed lower voltages.
If you don't have one, buy one. Seriously. It's the single most important piece of equipment you need when repairing mains appliances.
And keep in mind that even if it is connected by an isolating transformer, you may unintentionally have grounded the DUT with a test lead from a mains-operated T&M equipment.

 - The fact that the RCD doen not trigger with PE disconnected, suggest that the high voltage is arcing to a ground plane somewhere. Switch lights off and trigger the tick. Do you see arcing somewhere?
 - Check the PCB for burn marks.
 - Remove all the flux. Looks like someone had a go at this. Flux attracts moisture and can cause an isolation leakage.
 - Measure resitance from Mains to PE and make sure the isolation is okay. Obviously disconnect from mains first.
 - Check the opto couplers (the white 6-pin ICs). These can fail without visible signs. You can find good tutorials on how to test them on YT.
 - Check all diodes.
 - Remove all connectors and see if there is burning/arcing inside.

If it's none of all that, an HV probe and a digital scope will be needed. DO NOT USE A NAKED MULTIMETER ON THE HV PART. Especially if its a chinese cheapo one. But not even if it says Fluke Cat IV on it. Unless you have a nurse fetish. Then go right ahead and put yourself in hospital.

What T&M Equipment do you have available?

[decsystem20]

It took some time until I could get back to the unit,  but here we go:

- The fact that the RCD doen not trigger with PE disconnected, suggest that the high voltage is arcing to a ground plane somewhere. Switch lights off and trigger the tick. Do you see arcing somewhere?

No arcing to be seen anywhere...but,

 - Check the PCB for burn marks.

There are no burn marks on the main PCBs but, at the rear of the PCB that holds the tube connector and is hidden behind the Fan, I found the black mark seen in the attached photos. --> Now the photos should be attached.

Finally a step into the right direction!

Now, what's the cause for the arcing?
- Dust on the PCB?
- Trigger voltage too high?
- Connections too close? (The sockets are actually quite loose in the connector)

Why does it trip the RCD when the unit is just switched on?
- Erratic behaviour of the trigger circuit? ("false trigger" during power up)

Would it be advisable to insulate the connections where the arcing occurs and give it a try?

 - Remove all the flux. Looks like someone had a go at this. Flux attracts moisture and can cause an isolation leakage.

I had a go on this but I'll clean it up as sson as possible

 - Measure resitance from Mains to PE and make sure the isolation is okay. Obviously disconnect from mains first.

The meter shows "OL"

 - Check the opto couplers (the white 6-pin ICs). These can fail without visible signs. You can find good tutorials on how to test them on YT.

This is the next one on the list.

 - Check all diodes.

Diodes were all good, nevertheless I exchanged all of them, did not change anything
Resistors have been checked as well, all good.
Except for the Trigger Transformer all parts I have removed so far are good, as far as I can test them.

 - Remove all connectors and see if there is burning/arcing inside.

All connectors are clean.

If it's none of all that, an HV probe and a digital scope will be needed. DO NOT USE A NAKED MULTIMETER ON THE HV PART. Especially if its a chinese cheapo one. But not even if it says Fluke Cat IV on it. Unless you have a nurse fetish. Then go right ahead and put yourself in hospital.

None of the tools I have available could measure stuff like the ~10kV pulse of  the Trigger Transformer...so why should I try this?
And if I had tried it I might not be able to post here...

What T&M Equipment do you have available?

Multimeters: Fluke 87 V, Amprobe 38XR-A
Scope: PicoScope 2205 MSO
Misc: ELV ESR Meter, ELV Capacitor capacity Tester, LCR-TC1, TL866 II Plus

Thanks for your help so far!

Regards,

Jens

[decsystem20]

As it seems the arcing happened underneath the connector.
Much worse than I expected it to be.

See the photos attached.

[thinkfat]

Yep, that looks pretty bad. It will keep arcing, the material is charred and carbonized. It's no longer good for high voltage isolation.

[decsystem20]

The connectors seem to be out of production, so a new one is not available.

I sanded the area where the arcing has occured and filled the "trench" with epoxy resin.
After reassembly I fired a lots of test flashes, so far everything seems to be working again.

I hope it will be a longer lasting repair.

The Main PCB is cleaned, the messy wiring is cleaned up as good as possible.