possible rewiring of a 115v Sigma Electronics VDA-26 PS for 230v? - Page 1
Forum section: electronics / beginners

author: pizzigri
author_rank: Regular Contributor
timestamp: September 05, 2021, 08:55:52 pm
content: Hi guys!Well, I'm stumped on a problem that possibly may have such a simple solution that it absolutely escapes me.Following the suggestions of this thread:https://www.eevblog.com/forum/testgear/10mhz-distribution-in-lab/msg1115180/#msg1115180I purchased a super cheap Sigma Electronics VDA-26 video distribution box, to use with my also quite cheap BG7TBL GPSDO.Fact is, I'm in EU, and the PS of the VDA-26 is for 115V, while I have 220V here.I opened the thing up, and I found an interesting silkscreen on the SSB-21 unreg linear power supply PCB.There are some pads with the 230V clearly printed.However, I could not find either the service manual or even a schematic, and even if the circuit seems quite simple, it makes little sense as a few things do not add up with the two transformer datasheet I found, both for primaries and secondary outputs.Has anyone ever managed to play with one of these and can tell me how to mod it so that i can reuse the PS wired for 220v, if that is even possible?Or should I just use a downconverter for it (which I tested the thing for proper operation BTW so I already have it), however unelegant that may be.ETA: VDA-26 in the title.Here's some pics:

author: David_AVD
author_rank: Super Contributor
timestamp: September 05, 2021, 09:20:23 pm
content: It looks like each transformer has 2 x 115V primary winding that are connected in parallel.The 2 thin traces under the 230V marked area look like they are the default 115V links that puts the two transfromers in parallel.It *could* be that cutting those two thin traces and linking the top two (at 90° positions) will get you the 230V option.Measure the resistance of overall mains input now. After the cuts / linking the reading should be four times higher.Please not that this is purely based on what I can see in those photos.

author: james_s
author_rank: Super Contributor
timestamp: September 05, 2021, 09:58:10 pm
content: If you can find a datasheet for the transformers then that will tell you everything you need. Otherwise use an ohm meter to figure it out and draw a schematic of the primary side, there is not much there so it shouldn't be too hard. You will end up doing exactly what David mentions, taking the primary windings that are currently in parallel and wiring them in series. When I have designed devices around similar transformers I placed zero ohm jumpers on the PCB and labeled them 120V and 240V, that makes it really easy to install the correct ones for the desired voltage. I don't have the mental energy today to trace the circuit for you from the photos but if you post the circuit I can confirm the necessary changes.

author: edpalmer42
author_rank: Super Contributor
timestamp: September 05, 2021, 10:02:44 pm
content: FYI, Sigma Electronics is now Sigma Technology Systems (www.sigmatechsys.com). They have manuals for the power supply and the amplifier itself, but they don't include info on how to change the mains voltage. However, an email may get you a definitive answer. It wouldn't hurt to include pictures of your power supply.

author: bdunham7
author_rank: Super Contributor
timestamp: September 05, 2021, 10:22:10 pm
content: Here's the datasheet:https://belfuse.com/resources/datasheets/signaltransformer/ds-st-lp-series.pdfI can't make sense of your board--is it more than two layers???What you have now is the transformers have their primaries connected in parallel, then they are connected in parallel as well. What you want is to rearrange things so that each individual transformer has its windings in series, then connect those in parallel to the 230VAC. What you don't want is to leave each transformer with its windings in parallel and then connect those in series. There appears to be some facility for doing that with the board, but I can't see it.

author: WattsThat
author_rank: Frequent Contributor
timestamp: September 05, 2021, 11:06:05 pm
content: Cut the two pc traces on the back of the board that join 1-3 and 2-4. You’ll want to remove at least 3-4mm of the foil between the vias for proper clearance/creepage distance.Then clean out the vias on 1 and 2 and solder a jumper between 1-2.Do not jumper 3-4, that would short the mains and clear the fuse.

author: pizzigri
author_rank: Regular Contributor
timestamp: September 06, 2021, 06:51:31 am
content: Thank you everyone! I just drafted the input part of the pcb, here it is....It’s a double layer, red is bottom and black is top.So I just need to cut the thin traces on the bottom and connect 1-2? That is simple!

author: bdunham7
author_rank: Super Contributor
timestamp: September 06, 2021, 01:37:38 pm
content: Quote from: pizzigri on September 06, 2021, 06:51:31 amYes. That results in the non-ideal solution I mentioned because it depends on the output load being balanced. However, this is clearly how they designed it to be converted, so go for it.

author: WattsThat
author_rank: Frequent Contributor
timestamp: September 06, 2021, 03:10:56 pm
content: Quote from: bdunham7 on September 06, 2021, 01:37:38 pmDoesn’t matter, loading is the same as both secondaries are in parallel. Looks like someone got clever to work around a transformer height restriction.

author: pizzigri
author_rank: Regular Contributor
timestamp: September 08, 2021, 03:55:11 pm
content: So I did as suggested, cut both traces and placed a jumper between pads 1 and 2. Measured about 950 Ohm between the mains wires (from around 240 before the mod), so all good. I connected to the 220v grid and everything is fine!It works! So thank you everyone.Franco

author: james_s
author_rank: Super Contributor
timestamp: September 08, 2021, 08:15:17 pm
content: Good to hear it all worked out.