AWG-2005 function generator output voltage

[Rachie5272]

I have a Gw Instek AWG-2005 arbitrary function generator with a strange problem.  For the most part it works properly, except in the 0.2-0.6 Vpp output range.  It will output a signal above and below this range, but drops to zero in between.  Interestingly, this range corresponds with a relay click.

By probing around with a scope, the signal seems to disappear in the relay which clicks in this range.  I can't figure out why though.  Testing the relay with a multimeter gives expected continuity readings, and the only nearby components are SMD resistors, capacitors, and the back EMF diodes.  Not the sort of parts which typically go bad.

The relay in question is RL302, on the right of the group of three relays.  TP106 to the right of this seems to be the signal before attenuation.  The resistors below the relays seem to be the signal attenuators.

Any suggestions on what to try next?  Pull off the relay?

[Rachie5272]

I think I found the problem, but it creates more questions than answers.

I was probing around looking for clues, when I decided to check the resistors.  Both R309 and R311 read completely open.  I reflowed the joints, and made sure to jab my probes well into the solder bead, but still nothing.  All the other resistors read close to their stamped values (accounting for in circuit networks).  The resistors in question are labelled "93R1" and "82R5", which should be 93.1 and 82.5 ohms.

My theory is someone shorted the function generator output to a voltage rail, which caused a large current to flow through these resistors, burning them out.  It's a rather bad design if this is the case.  The BK Precision function generator I have at least put a fuse on the main output.

Now for the hard part: buying two SMD resistors without paying 1000 times their value in shipping.

[alex.forencich]

What about picking up an SMD resistor kit?  There are a few on ebay for ~$40 or so IIRC that have a gigantic range of values.  Might come in handy for other projects as well.  Otherwise, it might be advisable to wait until you have to order a few other things so you can amortize the shipping cost. 

[saturation]

Good job finding the fault.  Resistors failed open without signs of failure is odd.  Nevertheless failing open is good as you can carefully clip a known working resistor atop the failed part and insure the unit now works as specified.

Methinks whatever the cost of these resistors is far less than buy a new AWG 2005.

You could add the output fuse yourself and thus prevent a future failure.   IMHO many FG I encounter have limited output protection and no fuses, so as  rule I assume all FG are similar. 

http://cp.literature.agilent.com/litweb/pdf/5989-8790EN.pdf