My next oscilloscope: Agilent DSOX2012A or DSOX3012A

I’ve needed a new bench oscilloscope for quite some time, both for work-from-home activities and for my hobby activities. I have an old HP54501A, but the NVRAM died in it years ago. When I bought a replacement system board with new NVRAM, it continued to have problems. In addition, the sampling rate is abysmally slow, making to only useful for slow or very repetitive signals. It is essentially useless for glitch-hunting activities I’ve needed to perform in the last 2 years, forcing me to use one of the $20,000+ scopes in the lab at work on several occasions. The old Tektronix TDS460 on my desk at work isn’t even sufficient for some of the things I’ve needed to do.

I’ve looked at several of the dirt-cheap scopes. The Rigol units from the DS1102E upward, the Owon units, the lower-priced GW Instek units, etc. However, their updates rates are not good (the Owons are terrible at around 32 waveforms/sec), the build quality is poor (especially on the Rigols), and the firmware isn’t terribly robust. They are an incredible bang for the buck, especially for the casual hobbyist, but they are not tools I can count on to save me time (and hence money) for advanced hobby use and professional use. Of the units I’ve looked at, the only truly appealing ones are the Owons for their portability (battery is an option) and deep memory. They are essentially incapable of finding signal glitches due to their very low waveform capture rate; I’d only consider one for portable use on repetitive signals, or in cases where I need basic MSO capabilities for dirt cheap.

In 2011, Agilent released a series of game-changing oscilloscopes in the InfiniiVision 2000 and 3000 X-Series oscilloscopes. The big deal: a 50,000 waveform/sec capture rate thanks to an Agilent-designed ASIC, at a price point of $1200 for the base 70MHz model. The 3000 series (starting at around $2800) will do 1,000,000 waveforms/sec! These new oscilloscopes can find signal glitches at rates previously only attainable at a price point in excess of $5000, which is well beyond what can be justified if you’re not making money daily with your oscilloscope. The build quality is well above the Rigols, Owons and GW Insteks. The screen is an 8.5″ WVGA (800×480). And you can start with a base unit and purchase additional features as needed, many of them being only software license changes (the feature is already in the base model, it just needs to be unlocked via a license key).

I’ve essentially never needed a 4-channel scope, except when I need MSO or serial bus decoding features. So I’ll likely start with the DSOX2012A and later add the MSO option. The only things that have me considering the more expensive 3000 X-series: more triggering features, and a lot more upgrade options especially for bus decoding and triggering. And some of the upgrade options have more features than the 2000 X-series. For example, the waveform generator can do arbitrary waveforms whereas the 2000 can not.

Repairing my Monster HTS 3500

I have an older Monster HTS 3500 that died some time ago. In the interest of not putting it in the landfill, I took it apart today to see what’s wrong.

One of the MOVs is toasted. It’s a Ceramate GNR20D201K. I can’t be sure, but I’m assuming a lightning strike or the like took it out. Don’t ask me why there isn’t a gas surge suppressor in here. Cheap construction would presumably be the answer, but I don’t have a schematic and don’t feel like digging too deep. I’ll replace the MOV and see what happens from there. I probably have some that I can scavenge, we’ll see.

Feb 8, 2012
I removed the burned MOV using my desoldering gun, and was about to replace it when I decided to check the thermal fuse that’s squeezed between the first two MOVs. It is open, so I need to replace it. It appears to be an SF139U, which as near as I can tell is no longer made. But it was 10A, 250V, 142 Celsius. I checked the other thermal fuses and they’re all good. I ordered new thermal fuses from Digi-Key, part number 317-1134-ND. I don’t have the same tape that Monster used to keep the MOVs near the thermal fuse. I’ll likely just use powdercoating tape since I know it’ll survive higher temperatures than the thermal fuse and I have some on-hand.

To make sure this would fix things, I shorted across the leads of the open fuse. Sure enough, the HTS 3500 comes to life and shows no errors. Hooray for some inexpensive troubleshooting and parts saving me a couple hundred dollars.

Feb 13, 2012
I replaced two MOVs and the thermal fuse, and all is well. I put the case back on and it’s ready to go back in the family room.