Voltech PM300 issue - Page 1
Forum section: electronics / repair

author: WitchHunter11
author_rank: Newbie
timestamp: September 25, 2019, 11:16:17 pm
content: Hi all, first post on this board. So I picked up a Voltech PM300 power analyzer for cheap, the issue being that the display was not working. I powered it on and it was just displaying horizontal black lines (see pic). Also, the front panel buttons don't seem to be responding, some of them are lit up and I'm not sure if the others should light up or not when pressed (they don't right now). Can't find ANY schematic/service manual for this. Other than that, the machine itself seems to be working fine. So I figured I'd start out by replacing the display.. no change. Still get the black horizontal lines. Could it be an display chip problem maybe? Maybe something with the power supply? I'm more of a beginner/intermediate to this... anyone have any tips on where to start troubleshooting? Thanks - Ryan

author: coppice
author_rank: Super Contributor
timestamp: September 25, 2019, 11:33:27 pm
content: If the display and the keyboard do not function correctly, how are you determining that "other than that, the machine itself seems to be working fine"? Are you using the GPIB interface, and getting proper operation there? If it works through GPIB, and a new display doesn't improve things, I would look at things common to the keypad and the display - e.g. the connectors between the boards.

author: WitchHunter11
author_rank: Newbie
timestamp: September 27, 2019, 07:56:46 am
content: Hi and thanks for the response. Well I don't know for sure whether it's JUST something in the display circuitry, or if it's something further down the chain that's affecting that and the keyboard/buttons because I just don't know how the buttons/keyboard are supposed to respond, whether they light up when certain buttons are pushed etc., I've tried doing the test when you power the machine on, pressing the < and > buttons adjust the lcd brightness but it does nothing, the screen stays consistently bright, that's why I suspect it might be something affecting the display and the keyboard. The machine powers on and seems to "run" OK, "seems" being the key word. I have no way of knowing right now... That's an interesting idea about using the GPIG interface.. so with that I'm able to connect the machine to a different display monitor? I'd be able to tell immediately if it's just the display circuitry in that case. Only problem is GPIG to USB adapters (which is what I'd have to use) are like $150

author: Kilrah
author_rank: Unknown
timestamp: September 27, 2019, 08:03:03 am
content: Didn't Dave have one with the same issue where he made a video about repairing the LCD?

author: tunk
author_rank: Super Contributor
timestamp: September 27, 2019, 09:56:31 am
content: I haven't done it myself, but it looks like you can use an arduino, e.g.http://egirland.blogspot.com/2014/03/arduino-uno-as-usb-to-gpib-controller.html

author: Leighcrx
author_rank: Newbie
timestamp: September 27, 2019, 09:59:40 am
content: Sounds like the problem is further back than the display ie processor. Have you checked the input to the display to see if it is actually getting sent any dataYou will find it impossible to find Voltech Schematics anywhere. I used to make/test and debug Voltech's Ati transformer tester, they were interesting.Dave, did a screen replacment video on one of these not long ago.

author: WitchHunter11
author_rank: Newbie
timestamp: September 28, 2019, 04:01:02 am
content: Quote from: Kilrah on September 27, 2019, 08:03:03 amI watched the 3 videos Dave did on this machine and it is most definitely NOT the same problem. His machine was usable, the display was just missing a few characters. Mine is completely unusable at the moment.Quote from: tunk on September 27, 2019, 09:56:31 amSo after delving into this idea of using the GPIG interface to try and control the machine from an exterior controller, I've discovered it's probably not possible. According to the user manual, in order to utilize the GPIG interface it needs to be set up USING the Voltech machine itself, so I'd need to be able to navigate through the Voltech's menu, which I can't do... was a good idea though.Quote from: Leighcrx on September 27, 2019, 09:59:40 amYeah.. I'm starting to figure it's probably something further back than the display processor because it seems to involve both the display and the keyboard.. I really WANT to scope the input to the display, I would love to, but this has got to be one of the most ridiculously inaccessible pieces of gear I've ever dealt with, the way the top portion has to close into the bottom is just really dumb (watch Dave's video to see what I mean).. just going to keep trying to figure this one out.

author: coppice
author_rank: Super Contributor
timestamp: September 28, 2019, 04:08:53 am
content: Quote from: WitchHunter11 on September 28, 2019, 04:01:02 amIf you think this instrument is inaccessible you should look around more. Its very common for instruments from smaller manufacturers, especially instruments for niche applications, to be a nightmare to work on. They just don't have the resources to develop the design until it is easy to manufacture and support. If it works, it ships.

author: WitchHunter11
author_rank: Newbie
timestamp: September 28, 2019, 05:15:26 am
content: Quote from: coppice on September 28, 2019, 04:08:53 amWell it basically requires sticking a hand into about a 2"x4" area surrounded in high voltage and praying you can get a scope probe on a pin that you can't see because it's on the back of a board that can't be shifted around because it's attached to both the top and bottom of the unit.. if there's something more inaccessible than that, I'd rather not see itI might try and rig up some kind of flexible probe or something.. I don't know.

author: njmicheli
author_rank: Newbie
timestamp: February 11, 2020, 02:16:54 pm
content: I agree that this does not appear to be the same problem shown in Dave's videos.I have 2 units at my job that show the same black horizontal lines. I attempted the screen replacement guided by Dave'svideo, with the exact screen and modification. No luck.According to the pinout on the new LCD screen (NHD-24064http://www.newhavendisplay.com/specs/NHD-24064WG-AYYH-VZ.pdf)I measured:Pin 3: 4.2VPin 4: -7.6V (after modification)Pin 5: HighPin 6: HighPin 7: High (This is our chip enable which is active low)Pin 9: -10.22VPin 10: LowPin 7 being high says the LCD driver chip is not enabled, so I traced this back to the main cards. The small interconnectboard is only a pass-through for this signal to the large bottom board (BTW, this interconnect board was swapped from aknown working unit as a test, also no luck). There it comes from the output of a NAND gate, which jumps through a bunch of logic gatesbefore that and ultimately ends up at the EEPROM chip (U40) and SRAM chip (U41).I checked the operation of NAND Gate U25 (which delivers the Chip enable signal) and it worked. All logic gates share thesame 5V bus, which was present. Since my keyboard also is not responding (the contrast buttons do nothing to my screen or theVo signal on the LCD screen), I would think that the common point is our EEPROM chip.Eventually another one of these will fail, and hopefully for another reason - at which point I'll swap the chips andsee if it comes back to life.

author: tutuural
author_rank: Newbie
timestamp: March 16, 2020, 01:20:50 pm
content: Hi,I just got my PM300 and noticed few very bad issues(I have tested this with two different devices). I feel now that whole meter is just boat anchor.When measuring 3 phase 4 wire mode, it can only measure channel 1 properly. If there is resistive load across phase and neutral in phase 2 or 3, it does not show anything except if there is some load also between phase 1 and neutral.If i put 80W in phase 1 and 1000W in phase 2. It shows only 21.75watts in phase 2.When changing mode to '1 phase and 2 wire' each channels shows right value, but then you have to use display button to scan each channel individually.Any idea what causes this or is this feature of this device?