Tek DPO Power Issue - Page 1
Forum section: electronics / repair

author: VE7FIM
author_rank: Contributor
timestamp: September 26, 2016, 07:38:28 pm
content: I've been looking at a used Tektronix DPO7054 as a possible new oscilloscope for the lab. Out of the box, when plugged in, several red and green LED indicators on the lower board to the far right of the unit illuminate, so I know it's getting power. According to the service manual, this is expected behaviour when the unit is in standby.When the front power button is pressed, several relays switch on, the power light on the power button momentarily turns green, the red LED momentarily turns off, but then the unit immediately powers down. At no point do the fans power up. Once this happens, the unit remains unresponsive until the power cord is disconnected and reconnected.The service manual has a pretty rudimentary troubleshooting guide at this point, instructing to remove boards one at a time to isolate the problem. However, if I open up the unit, I will lose the ability to return it, and replacement boards are quite expensive. At the same time, if it's something simple like a loose cable, I'd prefer not to return it without fully checking the system out.Any suggestions for things I should try? Has anyone encountered a similar issue with their Tek 7000-series scopes?Thanks,David (VE7FIM)

author: Jwalling
author_rank: Unknown
timestamp: September 26, 2016, 08:49:09 pm
content: Possibly of no use in your situation, but some Agilent scopes (54830X series for one) will do a shutdown if the fan(s) are detected to be non-functioning. Since the fans in your scope aren't spinning up...IIRC they don't use a tach signal, but measure current draw for some odd reason.

author: David Hess
author_rank: Super Contributor
timestamp: September 26, 2016, 09:35:26 pm
content: Quote from: Jwalling on September 26, 2016, 08:49:09 pmMy hardware RAID card does this and measures the fan rotation using the ripple current. I think manufacturers do this because fans without tachometer inputs are more universal.

author: VE7FIM
author_rank: Contributor
timestamp: September 27, 2016, 01:01:02 am
content: I checked both of the main fans, and they spin freely, however, there are at least three additional fans out of reach, deep inside the scope.Given how quickly the power cuts back off, I suspect something is tripping the power supply protection circuits, either too much current draw (which would imply something other than the power supply is broken), or one of the rails is out of spec (which would likely mean it's the power supply that has failed). Just out of curiosity, I've put in a request to Tek to find out how much a replacement power supply would go for. It's part #119-6986-00, and appears to also be used in the AWG7000 series.We'll see what they say.

author: VE7FIM
author_rank: Contributor
timestamp: October 04, 2016, 12:39:27 am
content: Looks like the scope is going to have to go back.Contacted Tek almost a week ago to try to get a price quote on a replacement power supply — no response.

author: nctnico
author_rank: Super Contributor
timestamp: October 04, 2016, 02:02:12 am
content: I don't think buying a new PSU blindly is a good idea. Either return it or open it & fix it. It does make me wonder who sells a broken scope with the right to return it.

author: Jwalling
author_rank: Unknown
timestamp: October 04, 2016, 09:33:18 am
content: Quote from: VE7FIM on October 04, 2016, 12:39:27 amDoesn't that scope have an x86 type PC motherboard in it? Could be a soft power on problem. Try checking the CMOS battery if so.

author: VE7FIM
author_rank: Contributor
timestamp: October 04, 2016, 04:04:16 pm
content: The company that the scope was purchased from is reputable, and I am certain that the scope worked when it was sent. Unfortunately, at some point during the month and a half long DHL nightmare where it was lost in a warehouse, found, sent to Northern Alberta, etc, it's operational state evidently changed.It does have a "relatively" standard x86 motherboard, but the disassembly process to get at it is quite involved, and would void my right of return. If I didn't have that option, I'd have pulled it apart long ago, and posted pictures too.The symptoms are consistent with a PS rail being either too low voltage, or too high current being drawn, but I can't troubleshoot it any further.Does anyone have a DPO 7000 series scope up for sale? There's a few up on eBay, but they're priced a little high based on what these have been selling for in the past.

author: nctnico
author_rank: Super Contributor
timestamp: October 04, 2016, 05:01:44 pm
content: If it was damaged in shipping then it is the seller's responsibility. How about sending it back and the seller fixes it or sends a different one? I'm sure a reputable firm wouldn't make a big hassle out of it.

author: VE7FIM
author_rank: Contributor
timestamp: October 04, 2016, 05:55:28 pm
content: Quote from: nctnico on October 04, 2016, 05:01:44 pmExactly. That's the plan, but it depends on if they have another unit in stock. Just haggling over who pays for return shipping.

author: VE7FIM
author_rank: Contributor
timestamp: November 12, 2016, 10:31:15 pm
content: Good news. The scope was returned, and I got a complete refund.Someone else was selling a scope with exactly the same problem on eBay, so it looks like this "click of death" failure mode is fairly common for this model of scope.You'd think with such an expensive piece of test equipment, they'd either a) spend more time on their design and/or use better quality parts in the power supply, or b) use a modular removable power supply that is easy and inexpensive to replace.Sigh.