FY6600 Sig Gen Replacement PSU - Page 1
Forum section: electronics / projects

author: moffy
author_rank: Super Contributor
timestamp: August 07, 2025, 03:24:10 am
content: I have an FY6600 signal generator which while being a reasonable and cheap signal generator has a serious issue. The internal PSU is very noisy and can have large voltages with respect to mains gnd, up to 90V with lots of switching noise. A number of people have provided alternative PSUs and fixes for similar models with the same internal PSU which work well, but I was hoping for an all linear solution for the best noise performance.The main problem here is fitting everything, including the mains transformer or transformers into a smallish case that isn't very well ventillated.The specs are basically: +/-12V@150mA each and 5V@0.5ATrying to do that with a single transformer, while trying to minimise the heat disipation on the regulators is a challenge, which explains why the other couple of solutions I've seen use switch mode PSUs.Jaycar sells this transformer:https://www.jaycar.com.au/6-3-15v-15va-1a-multi-tapped-type-2155/p/MM2002Which fits and could work well, using the '6.3V tap' as the 0V for the 5V supply and the '0V tap' and '12.6V tap' as the rectified input to the 5V regulator. That the means that the '15V tap' relative to the '6.3V tap' would provide the rectified input to both the +/-12V regulators. A schematic is included to help make sense of the description.The '15V tap' minus the '6.3V tap' (all transformer voltages are RMS) just leaves 8.4V RMS or 11.9V peak which is not quite enough. A simple fix is to use a voltage doubler, peak of 24.2V, but then disipation rises which is not the best.The solution chosen is to use a 'fractional doubler', excuse the term it's the best I can come up with at the moment, perhaps there is a better term out there. Instead of refering the doubler part to the '6.3V tap' if it is refered to the '9.5V tap' then one ends up with a peak of (8.4 + (15-9.5))*1.4142V = 19.6V which is a bit more reasonable and allows for droop with increasing load.I managed to fit everything fairly neatly with a suitable heatsink and the FY6600 runs much better!

author: moffy
author_rank: Super Contributor
timestamp: August 08, 2025, 01:39:07 am
content: Just a few photos of the upgrade, the titles are self explanatory. Even with the limited ventillation the heatsink only gets mildly warm, I fitted an inline fuse in series with the transformer.

author: Someone
author_rank: Super Contributor
timestamp: August 08, 2025, 02:51:09 am
content: This is the sort of reason why electrical parts are ever harder to find at retail. You've degraded the electrical safety of the device without realising why.Some random transformer is not a replacement for a class II (isolated) supply, that requires specialised transformers (and wiring). While the chance of a problem might be low all the liability now sits on you if something does go wrong.

author: moffy
author_rank: Super Contributor
timestamp: August 08, 2025, 03:17:26 am
content: Quote from: Someone on August 08, 2025, 02:51:09 amI have no reason to distrust the mains transformer, sold by Jaycar and Altronics, and been around a long time in Australia. I do have every reason to distrust the supply which was replaced which is some generic Chinese supply with terrible isolation, I would suggest your viewing others on Youtube that have tested and replaced the same PSU in their generic signal generators. The chinese version is quite dangerous.

author: Someone
author_rank: Super Contributor
timestamp: August 08, 2025, 04:47:26 am
content: Quote from: moffy on August 08, 2025, 03:17:26 amJust digging in deeper there. The transformer you bought is not designed or warranted for the use you have put it to.Is the FY6600 even sold retail in Australia with Australian approvals?

author: MariuszD
author_rank: Regular Contributor
timestamp: August 08, 2025, 05:26:11 am
content: The transformer from Jaycar has windings on two separated sections. It can be reasonably assumed that this transformer has good insulation. In the picture, there are symbols of Class II insulation and a safety transformer. I suspect that this transformer has better insulation than the original Chinese power supply.

author: Someone
author_rank: Super Contributor
timestamp: August 08, 2025, 05:31:19 am
content: Quote from: MariuszD on August 08, 2025, 05:26:11 amSee how that picture is different to the unit that is shown by the OP ? Jaycar swap out suppliers/specs on their parts all the time while keeping the same part number.

author: moffy
author_rank: Super Contributor
timestamp: August 08, 2025, 05:45:30 am
content: Quote from: MariuszD on August 08, 2025, 05:26:11 amYes it is definitely split bobbin, with extended plastic guards around the windings, protecting both mechanically and electrically.