Dahua PTZ over-voltage - recoverable?

[awsum140]

I was wondering what in input Z of the meters used was. DVMs, generally have too high an input Z to be reliable for too many uses, plus the sampling rate issues. I have a cheap, low Z, VOM that I rely on for general DC and AC work. The Simpson 260 was my favorite though, it bit the dust after too many drops from ladders.

I replaced my outside floods with LED floodlights, but some of them would flash, one row of the array, about twice a minute when shut off. Nothing dangerous, I check voltage with the VOM and nothing showed, but it was annoying. I added .22uf/600v capacitors to those lines and got rid of the problem. We're about a mile from a 15KW AM broadcast station and I suspect RFI from that.

 

[tangent]

I was wondering what in input Z of the meters used was. DVMs, generally have too high an input Z to be reliable for too many uses, plus the sampling rate issues. I have a cheap, low Z, VOM that I rely on for general DC and AC work. The Simpson 260 was my favorite though, it bit the dust after too many drops from ladders.

I replaced my outside floods with LED floodlights, but some of them would flash, one row of the array, about twice a minute when shut off. Nothing dangerous, I check voltage with the VOM and nothing showed, but it was annoying. I added .22uf/600v capacitors to those lines and got rid of the problem. We're about a mile from a 15KW AM broadcast station and I suspect RFI from that.

I checked it again with an analog meter with the same result. The voltage slowly falls from about one to zero over about 40 seconds after it's unplugged. Generally I don't have a problem with a high Z meter, you generally don't want your measurement to alter the system.

As to Sean's problem, a working camera of the same model and one of these: MASTECH MS8910 Digital Multimeter Smart SMD RC Resistance Capacitance Diode Meter Tester Auto Scan 3000 Counts LCD Display-in Multimeters from Tools on Aliexpress.com | Alibaba Group would be a decent starting point after visual/olfactory inspection.

 

[looney2ns]

Exactly!

Neither the Triplett 630 or the Simpson 260 had a setting to expressly check capacitors but I'd put the dial on R x 1K (or 10k depending on the cap rating in uF) and check large filter capacitors in linear power supplies or smaller caps in Schmidt trigger timing circuits; you'd charge it up with the + and - leads of the meter on the cap one way, then reverse the leads and watch the charged cap decay. It wasn't an accurate test but experience would allow you to make a pretty good call that a 1,000 uF cap or a 100 uF was discharging too quickly or not storing a charge at all as it should. Only a low impedance meter would allow you charge up a cap with the meter's batteries like that (batteries used in the meter's internal Wheatstone bridge to calculate the resistance under test).

I love digital radio tuners, digital watches ( analog's OK, too), all kind of digital displays....but given a choice of only one meter I'd take a good analog VOM over digital any day.

It's not in the league of what you used, but I built this circa 1968.
It still works perfectly.

 

[awsum140]

Hey, Heathkit made some great stuff and, if you were careful and did the calibration right, were more than accurate enough for "government work".

 

[looney2ns]

And for the youngsters, it didn't have a single smb component. It use's a few of these instead.

 

[awsum140]

Mine was Senior VoltOhmyst. Great stuff I wish I still had.

 

[Fastb]

The VOM could read capacitance and had a button that would send a small pulse. With enough experience at watching the reading peak and decay, you could make a decent guess at the distance to the open.

Yes, the "poor man's" TDR.
The nice cat cable tester at work would do the basics (check all 8 conductors for shorts, opens, correct contact usage, etc). And it had the TDR feature. I the cat cable were open (cut somewhere along the run), or shorted, the TDR feature would tell you how far aways was the problem, in feet. Seemed like an awesome feature! I didn't use that feature much (thankfully, shorts and opens were an uncommon problem). But when I did use it, I had my doubts about the accuracy.
True TDR equipment used to be very expensive. The Cat cable tester didn't elaborate on how it figured distance. Instead of sending a pulse, and measuring the time for the reflection to return, I think it used a simpler RC test. Checking the "peak and decay" as @geezer described.

Fastb

 

[TonyR]

And for the youngsters, it didn't have a single smb component. It use's a few of these instead.

And for our friends in the UK...."valves".

 

[awsum140]

Back in the days of ethernet being only on coax, yeah I'm that old, we had a Techtronix TDR to certify the cable installation. It would show everything, down to tight turns and every tap in an RG58 run. When we did fiber optic, later in the ethernet business, we used an optical TDR that was even more expensive, but there's no other way to truly see what's happening where on a cable or fiber, not to mention getting a precise, as installed, length measurement.

 

[Sean Phelan]

Woah.... this thread has moved a long way since my first question about an apparently damaged camera

I just came back to say that the camera that I thought I had fried by connecting to 24V instead of 12V spent several months lying in a corner, then before throwing it out I tried patching the RJ45 connector to a PoE hub and... voila! Worked perfectly. It has been running live on PoE without any problems for about three months now.

So, lesson one: don't connect 12V devices to significantly higher voltages, and... those of us who have not learnt lesson one may benefit from lesson two: fairly obviously the power input circuitry is likely to be the initial point of failure; the rest of the device may be fine.