Polar Toneohm 580 Current Tracer questions - Page 1
Forum section: electronics / testgear

author: JC_Phoenix
author_rank: Newbie
timestamp: February 11, 2022, 05:07:51 pm
content: Hello all!I've been reading through the many excellent threads on the forum related to the Polar Toneohm equipment (I have a Toneohm 550 eBay special with homemade probes), but I have a couple of questions on the Toneohm 580 current tracer schematics.Looking at the schematic, I can't determine what part number of the transformer is. Does any know an equivalent item? Not owning one yet, I've no way to know, and there are no parts lists for these units that I can find, only the schematics.My other question is what would be the voltage measurement that would come from the D3 diode at that transformer to what appears to be the emitter of the Q1 transistor. Or to put it another way, what's the input voltage to the 7805 that's also connected to it? Hoping someone might know offhand.Cheers!

author: JC_Phoenix
author_rank: Newbie
timestamp: February 13, 2022, 05:20:36 am
content: No takers, huh?

author: Shock
author_rank: Super Contributor
timestamp: February 13, 2022, 01:37:16 pm
content: Welcome, looking at the schematic or image you provided we can clearly see, nothing. The 7805 or 78L05 specs you can google to find suitable input voltages.Looking at another design of theirs had 9V AC on the transformer outputs, so 9-12V would be reasonable to assume. Unless it's marked, measured or documented it's hard to tell what transformer it uses but it looks like there is space to retrofit one if you had to.These look like they can be configured 230V or 115V so a transformer swap would only be required if defective,

author: JC_Phoenix
author_rank: Newbie
timestamp: February 13, 2022, 03:20:34 pm
content: I was thinking somewhere up to 12 volts would be likely, but as you said, there are no details on the schematic. It would be really helpful if they showed the windings information on there, but no such luckI do have the 550 unit, I wonder if the transformer is compatible? In which case I might be able to find a meaningful part number if I open that up and take a look. It needs calibration, so I need to open it anyways.Of course, if Polar produced a parts list, that would be nice, tooThanks!

author: JC_Phoenix
author_rank: Newbie
timestamp: February 13, 2022, 11:56:43 pm
content: Looking inside the 550 today, the transformer is a 120/240v - 9v unit. The only part number I can see on it is MEP MW3552, which I haven't been able to find out much on when I check online. I'll presume it's similar to what's in the 580 until I get better information.The trick now is trying to find an equivalent online.

author: JC_Phoenix
author_rank: Newbie
timestamp: February 14, 2022, 02:35:46 am
content: Based on some further research, I can't find anything on the Net matching that part number, but based on the similarities between both the 550 and 580 power sections in the schematics, it seems that they likely both use the same dual primary, dual secondary 120V x 2 to 9V x 2 3VA transformer.I took the dimensions of the device when I had the 550 open for calibration, and found a similar spec unit from Vigortronix, part number VTX-120-3803-409.They also make a 6AV version, part number VTX-120-4206-409. I may pick up that one instead if it's not too much more expensive.

author: JC_Phoenix
author_rank: Newbie
timestamp: February 15, 2022, 02:19:51 pm
content: I've found some equivalent devices, but most all are out of Britain, so the postage cost is silly. I'll shop around, and maybe next paycheckThey seem to be extremely difficult to find from U.S. vendors. Very strange.

author: Shock
author_rank: Super Contributor
timestamp: February 16, 2022, 01:31:32 am
content: It only needs 115V (120V) on the primary if it's intended for US use, but since it's PCB mounted some modification may be required. You will also need to get the phasing of the secondary right I suspect.

author: JC_Phoenix
author_rank: Newbie
timestamp: February 17, 2022, 05:04:23 am
content: My (possibly flawed) understanding is that because it has dual 9v secondaries, it needs to have dual 120v primaries. I'm clearly no expert in transformersHowever, if it's possible to use one with a single 120v primary that would make the search much easier (and cheaper) It's not like it needs to run on 240v, ever.The schematic doesn't show any phasing information, unfortunately. Funny thing is, the 700 does show the phasing information. Maybe that means it can be presumed to be something with no exotic winding configuration?

author: Shock
author_rank: Super Contributor
timestamp: February 17, 2022, 07:36:17 am
content: As I mentioned before though it looks board configured 115-230V, so you may need to mod the traces if it's not an exact replacement (but otherwise a good pin fit). Don't want to slap in a 115V/120V transformer without making sure it wired for 115V on the correct primary pins and there aren't any other traces that will cause shorts.I imagine this is why you are going down this path, someone probably blew it up on 230V. If transformers are fused properly normally they are fairly robust.

author: JC_Phoenix
author_rank: Newbie
timestamp: February 17, 2022, 01:43:53 pm
content: The modding shouldn't be any problem, I just need to be sure before I attempt it that replacing a unit containing two parallel 120v primaries with a unit that has a single 120v primary is workable, (assuming the replacement device is designed to output two 9v outputs like the original, of course) The schematics show how to handle the wiring side of things, so I've got that covered.