Signal generator fail  - Page 1
Forum section: electronics / general

author: Michaelpier
author_rank: Contributor
timestamp: August 29, 2011, 09:31:27 am
content: I finally did what i was afraid.One channel of the rigol function DG1022 generator is burned.I connect it trough a kenwood amplifier cause of the need for higher power, by connecting the output of the generator to the input of this kenwood amplifier.http://images03.olx.in/ui/3/78/55/45697355_1.jpgStill have the 2nd channel but iam afraid not to destroy that one too.What kind of circuits i can use for the protection of the function generator?Thanks

author: Psi
author_rank: Super Contributor
timestamp: August 29, 2011, 09:41:07 am
content: With a working channel its much easy to fix these sorts of things, since you have a working circuit exactly the same as the dead one which you can compare against to locate the blown component.I'm not sure how you managed to blow up a port on the siggen by connecting the output to an amp input.Was the amp floating or something?

author: saturation
author_rank: Super Contributor
timestamp: August 29, 2011, 03:46:23 pm
content: Sorry to hear. To protect the input you need a voltage follower, with an op amp designed for the proper unity gain; see mechatrommer's circuit for the Hantek 3x25 on the thread.However, the preamp input for a standard audio amp should not cause anything to blow, since its relatively new I would suspect a Rigol quality defect; even if you short circuit an FG output it often has a 50 ohm output resistive impedance; at the most the op amp will heat up; IIRC the input impedance to audio amps are fairly high, in the 100s of ohms.

author: Unknown
author_rank: Unknown
timestamp: August 29, 2011, 04:45:18 pm
content: I concur, it seems unlikely that connecting it to an amplifier will destroy it. Lab grade function generators are almost always designed to survive shorted outputs. Audio amps tend to have an input impedance in the tens of kohms. The main way to kill a generator is by feeding it current somehow. For example, by connecting the output to a voltage source, or by connecting it to a huge inductor.

author: d3x0r
author_rank: Newbie
timestamp: January 10, 2012, 05:27:00 am
content: Quote from: Psi on August 29, 2011, 09:41:07 amMaybe you can clarify something for me - what exactly is the 'float'? I have a similar problemI got an amp, connected the shield of the signal generator to the shield of a channel input and the center wire to the signal post of the same channel... I have a battery powering the amp that is separate from the signal generator - should I run a wire from the shield on the signal input to the - on the battery?The signal did seem to wander bigger and bigger, and then it stopped altogether. was a really slow oscillation of like 213milli hz.. is this a feedback that would cause damage?Would a fix for this maybe be a 1:1 transformer coil on a UBolt? (yes largely lossy but the amp should make up for it I would think)

author: amspire
author_rank: Super Contributor
timestamp: January 10, 2012, 06:22:57 am
content: Is the power cable of the Kenwood amp earthed or is it a 2 wire power cord?That fact alone wouldn't have blown anything, but if there is no earth on the amplifier, and if it had an internal fault causing mains leakage to ground and the generator was connected with the two wires swapped (so the center pin of the Rigol output was connected to the amp ground), that could possibly blow the generator output. Also was the amplifier connected to any other device at the time?A simple tests is to measure the AC and DC volts between the amp ground and the Rigol ground with the two not connected. If you see a significant voltage, connect the two grounds together with a 10K to 100K resistor and measure again across the resistor. If the voltage did not drop to a low level, then there is a problem somewhere.If the Rigol is under warranty, it is definitely worth getting Rigol to fix it, If nothing obvious was found in the test above, it is unlikely the Rigol is a charred mess inside to indicate abuse from you, and this could have simply been a fault waiting to happen in the Rigol. For example, I remember when we implemented a full ESD handling procedure in an assembly plant that previously had a sloppy procedure, returns within the first two years went down by a factor of 10. If someone mishandles an IC during assembly, it can put a micro puncture between layers near an input pin on the substrate that usually allows the part to function, but localized heating at the puncture point will almost certainly cause the IC fail within a year or two. ESD mishandling doesn't destroy parts outright very often.So the failure is not necessarily your fault, but the load resulting from the connection to the amp may have tipped a failing part over the edge.Richard.

author: hacklordsniper
author_rank: Frequent Contributor
timestamp: January 10, 2012, 08:11:06 am
content: If the Rigol is out of the warranty and you dont have desire to fix it i will be happy to buy it from you.