Electronics > Repair
Wavetek 2520a 0.2-2,200MHz RF sig gen repair
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tautech:
See you Thursday arvo with the rescue package.
dazz1:
Hi
I identified 5x 1uF Tant Caps connected to the +15V regulator output.   At least one of them had a short.
I went through and destructively checked each cap.  I cut a lead and lifted each cap for testing.
Naturally it was the last cap that I tested that had the short.  This positively confirmed I had identified the faulty component.

It takes me not very much time to remove the main pcb having done it a few times. 

I am now replacing all 5 tant caps.  If there are no further faults, the 2520A should be fully operational again. 

Dazz
tautech:
I've seen Defpom replace caps only soldering the top side pad but providing sufficient dwell time to let the solder wick through to the pad on the other side so to not need to remove PCB's that might be difficult to remove.

Guess you got my mail explaining I how won't be done until Welly sorts out their Covid situation.  :scared:
2 weeks I guess should have it sorted.
dazz1:

--- Quote from: tautech on June 23, 2021, 11:40:14 am ---I've seen Defpom replace caps only soldering the top side pad but providing sufficient dwell time to let the solder wick through to the pad on the other side so to not need to remove PCB's that might be difficult to remove.

Guess you got my mail explaining I how won't be done until Welly sorts out their Covid situation.  :scared:
2 weeks I guess should have it sorted.

--- End quote ---

Hi
The leads are bent over on the underside.  I only have a rubbish single shot solder sucker, so clearing holes is a 2 sided operation.   Taking out the main pcb and cutting the leads was going to be easier that trying to do it all from the top. 
I have now got to the point if I find one failed Tant Cap, I replace all on the same power supply.  Another reason why I did destructive testing.    I am trying to avoid replacing every Tant Cap.  They are everywhere.

Testing converted a hypothesis (that a Tant Cap had failed) into a fact. Similar symptoms could have been produced by a failed device.

I'm looking forward to meeting with you but Covid disruptions are now a normal part of life.

Dazz
dazz1:
Hi
I think I have almost cleared the last fault.  I still have to replace the Dallas nvRAM.   Attached are images from the Siglent spectrum analyser with FM and AM modulation.  I used the internal signal (400Hz or 1000Hz) source, and the external 1000Hz modulation feature.  The external sig-gen is an Elector XR2206 based design.   OK but not a pure sine wave generator. 

The attached screen shots are functional tests only.  I was just looking to see if I have more faults to deal with.

Internally, the 400Hz/1kHz oscillators produce a 10V signal at full scale.
The external modulation signal input only requires 2.5V to match the internal signal.  There are a couple of images showing a 5V input signal, over modulating and over driving the Wavetek.

The modulated spectrum is quite messy as the modulation depth rises but I probably wouldn't use the modulation feature.  If I did, it would probably be good enough.
I haven't looked to see if there is another fault. 

The envelope shape for FM might be distorted because the internal/external modulation oscillators aren't great.  I wouldn't want to dive too deeply into finding a fault unless I can get access to a low distortion audio sig-gen.

Dazz



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