Synthesizer power supply replace - Page 1
Forum section: electronics / repair

author: diskosteppas
author_rank: Contributor
timestamp: July 29, 2021, 06:09:54 pm
content: Hi all would it be possible to replace this circuit in my synthesizer with an off the shelf power supply with one each of +15V -15v & 5v outputs?I have attached the schematic for the psu I do hope I hear from someone I fear buzzing

author: Audiorepair
author_rank: Frequent Contributor
timestamp: July 29, 2021, 06:31:02 pm
content: Not really.The original power supply has an LCD backlight supply at the top of the schematic which you would need to add to be able to see the LCD.Also, IC1 provides a reset signal, which amongst other things stops the processors from trying to boot until it has a proper stabilised 5v supply.So you would also need to add at least a delayed start reset signal on power up to make the machine reliable on boot up.

author: diskosteppas
author_rank: Contributor
timestamp: July 29, 2021, 06:44:31 pm
content: Hi thank you so much this is really enlightening thank you.I have seen a screen modification that I think uses a different 5V lcd but I have yet to implement it.So trying to weigh up options, I was eyeing up the meanwell supplies and definitely wondered.https://www.meanwell.co.uk/power-supplies/open-frame-power-supplies/pt-65-seriesorhttps://www.meanwell.co.uk/power-supplies/enclosed-power-supplies/rt-125-seriesI have read it is nigh impossible to find a suitable modern dropin trafo which is making me very anxious!Thank you for taking time out to reply.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: July 29, 2021, 07:15:38 pm
content: Well, if it is just the mains transformer that is unobtainable, it would theoretically be possible to replace that with an SMPS.But you would need one that supplies +/- 20v or so, and 9v or so, to mimic what comes out of the original transformer.And you would need to be able to find the space inside the synth to install this.From your Meanwell PSU links, you would need to find outputs of 9v, 18v, 18v, or 20v maybe.I think 9v, 24v, 24v might probably be too much, and the 15v original regulators would overheat, though the bridge rectifier drops things down a bit.It would be an experiment.

author: diskosteppas
author_rank: Contributor
timestamp: July 29, 2021, 07:39:23 pm
content: Thank you so much. I have been scrolling through all day looking at trafos and you have narrowed my search a great deal.I very much appreciate your advicethank you

author: Audiorepair
author_rank: Frequent Contributor
timestamp: July 29, 2021, 07:50:47 pm
content: Just modified my last post with further info.

author: TimFox
author_rank: Super Contributor
timestamp: July 29, 2021, 07:58:22 pm
content: Can you remove the backlight-drive circuitry around T1 and Q1, which runs off the +5V supply, and mount it with a replacement power supply?There are many commercial power supplies (linear or SMPS) that have +15, -15, and +5 V outputs.Similarly with IC1.

author: diskosteppas
author_rank: Contributor
timestamp: July 30, 2021, 06:10:23 am
content: Hi I'll have another look for something a little more powerful. It is an experiment and I know one day itll just give up at the moment it's buzzing.Thank you once again I am feeling so much calmer.

author: diskosteppas
author_rank: Contributor
timestamp: July 30, 2021, 06:11:46 am
content: There is a mod online that takes care of this indeed I will be trying this! I hope my results based on everyones contributions will also help preserve someone elses instrument for another 30 odd years. Such a shame to butcher it for parts!