TTi TG2000 repair

[cheeseit]

Yesterday I received my latest T&M purchase which has turned out to be a bit of a score, at least to me. Among five items were a TTi TG2000 which was sold as not working. Upon power-up the display turned on, with squares filling line one and three of the 4x20 character, and two internal LED's flashing briefly. No response to button input, no relays clicking and no beeping. Searched for a service manual or something but only found an instruction manual that was of no immediate use.

I checked the usual; cables and connections seemed fine, capacitors looked good, no visibly burned components, and voltages looked good too. Then I grabbed the DMM and started probing around. When I measured a few logic chips I found that some of them had no supply on the positive rail. I was not entirely sure if they should have supply at that stage, since the unit wasn't properly started - what do I know, I'm a newbie so don't laugh if that is ridiculous.
I started visually tracing the supply between vias and found one that had a tiny bit of green and looked clogged. By measuring continuity between front and back of that via I determined that there was none so I poked a bit of component leg through the via and soldered it to a cap on one side and to the trace on the other. Voila; the unit now fully works!

I'm feeling pretty satisfied now, considering I bought it from a tech that apparently has had it open before. And, not least, because a new unit costs €850 here in Denmark

Question: how can a single via corrode with no further visible damage to the area around it and far from any (electrolytic) capacitors?

[lowimpedance]

Neat repair and good score. I know the feeling of a nice repair and satisfaction of now having a nice bit of gear fully operational ....enjoy.
As to the cause of the corrosion well  , but since it happened once just make sure you give the entire PCB a good close up inspection for any other suspect 'green growths'.

[voltsandjolts]

I see a few other vias covered in solder mask, 'tented' as they say.
Sometimes tented vias trap chemicals from the PCB manufacturing process which cause corrosion over time.

[bitseeker]

Good eye, cheeseit! Congrats on getting the sig gen working. Looks like a nice one. I'm with voltsandjolts that the corrosion might have been some trapped contaminant from manufacture since it was so highly isolated. Just a fluke (no pun intended, or maybe it was).

[majki]

If you still have it could you please take some high res photos about the output stage of this device?
I wonder what kind of output amplifier is used.

The quite old thread https://www.eevblog.com/forum/testgear/tti-tg1000-10-mhz-dds-function-generator-internals/msg235324/#msg235324 mentions the list of IC within the TG1000, but none of them is good for the output.
The device is capable 20Vpp open circuit, but none of the mentioned high speed op amps are capable to deliver it.

Maybe the LTC1257 is mistype and it is LT1227?

[majki]

I got already a promise for photos in thread https://www.eevblog.com/forum/testgear/tti-tg1000-10-mhz-dds-function-generator-internals/?topicseen
So thank you