Help me find a transformer here. :) - Page 1
Forum section: electronics / repair

author: vze1lryy
author_rank: Regular Contributor
timestamp: May 08, 2016, 10:10:25 pm
content: I have an HCA-1000a from Parasound that I love very much - I fixed this when I was a teenager and it was my foray into hi-fi audio, and also my first audio electronics repair. a destroyed relay and a bad trio of output transistors. I remember saving up for a Sencore transistor tester just to match the batch I bought up to fix this over ten years ago - MEMORIES!!!There's still some garbage in there I want to un-screw-up like the wire over the broken relay... that I have had on hold for a long time, because it is not for a customer who can call to complain.the transformer is completely trashed.I emailed parasound. I haven't heard back yet, but am just brainstorming incase they tell me to kick rocks, we haven't made this in 20 years, no transformer for you. There aren't any specific voltages listed on the schematic unless I am missing something here,I understand completely how this isn't financially viable over just getting something else. I got it right around the time that my dad and I moved into our own new apartment and it was my first hobbyist repair that actually required electronics troubleshooting rather than just modifying/swapping a chip into something, so it has some sentimental value beyond its actual value. I want to keep this around!I attached a schematic.

author: DimitriP
author_rank: Super Contributor
timestamp: May 09, 2016, 04:33:17 am
content: QuoteThrow a post at diyaudio.comYou might get a response directly from the horse's mouth :http://www.diyaudio.com/forums/members/john-curl.html{edit spilling}

author: oldway
author_rank: Super Contributor
timestamp: May 09, 2016, 01:17:14 pm
content: Looking at the schematic, it seems to be 2 secondaries of 40 + 40 Vrms and an auxiliary secondary of more of less 10Vrms

author: nitrocaster
author_rank: Newbie
timestamp: May 09, 2016, 02:47:24 pm
content: Quote from: oldway on May 09, 2016, 01:17:14 pmWhy 40 and 10? How did you understand that?

author: SeanB
author_rank: Super Contributor
timestamp: May 09, 2016, 05:45:38 pm
content: 80V rated capacitors, so the maximum voltage on the secondary should not exceed 56VAC, so likely something lower, and 40-45VAC is a good voltage for safe operation of the capacitors. 10VAC because it is only there to provide power to the power on and off delay circuitry, and to power the indicator lamps. It would be fine with 9VAC to 16VAC.

author: oldway
author_rank: Super Contributor
timestamp: May 09, 2016, 10:18:28 pm
content: 125W / 8 ohms per channel = 31.62 Vrms or 44.72 VpeakIt means that dc voltage must be at least 50V at full power.No load voltage = 55VWith diode voltage drop, Uac = 40Vrms

author: albert22
author_rank: Regular Contributor
timestamp: May 10, 2016, 05:00:56 pm
content: As a last resort. With patience you can disassembly the transformer. Count the turns, measure the gauge of the wires and rebuild it. Or buy a new one with the data that you obtained.May be you can find a shop that could rebuild it for you.

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: May 11, 2016, 01:20:02 am
content: Here´s a tip. Buy a used MOT (try to get one free from your locale recycler). Remove the secondary winding. Rewind the secondary with 12 or 14 gauge insulated wire. Test it for voltage. If it buzzes, try to bolt it firmly to the chassis. It might get quieter but it probably will hum at bit. Just raise the volume of the stereo to quit it. You will not regret this if you are not afraid of ac line voltage.

author: Tube_Dude
author_rank: Regular Contributor
timestamp: May 11, 2016, 11:28:11 pm
content: It looks the rail voltage is around 60 Volts, according to this guy...http://forum.polkaudio.com/discussion/168019/hca-1000a-repair-refresh

author: oldway
author_rank: Super Contributor
timestamp: May 13, 2016, 05:56:29 am
content: Quote from: Tube_Dude on May 11, 2016, 11:28:11 pmWithout knowing if mains voltage is the nominal value or not, this does not means nothing.

author: Rasz
author_rank: Super Contributor
timestamp: May 13, 2016, 08:43:22 am
content: Quote from: joseph nicholas on May 11, 2016, 01:20:02 amhe will not regret spending couple of hours on manual labour to end up with humming transformer when you can buy proper one for $30?

author: vze1lryy
author_rank: Regular Contributor
timestamp: May 19, 2016, 02:45:42 am
content: Firstly, my apologies for not coming back to thank everyone for their answers for so long. This is a "passion project", meaning it only gets observed after work... which means almost never.I actually had a bad bridge rectifier that was blowing fuses. I have no idea what asinine line of troubleshooting led me to blaming the transformer.Replace that and bam, not blowing fuses. Even replaced the relay I ran wires over when I was 16.The actual power rails for this appear to be around +64vdc and -64vdc. either 54 or 64 after the bridge... I forget. Definitely above 50. I feel like I want to say 64 but reading your posts has me doubting what I measured earlier today on both channels.My issue now, I am guessing is somewhere in the symmetric cascoded differential gain part in the beginning.. which is filled with transistors that have not been available since I was in 5th grade. FML.Back to the bottom of the pile until I can find some substitutes. Thank you again for all the suggestions and help: I really appreciate it!

author: johansen
author_rank: Super Contributor
timestamp: May 19, 2016, 04:58:38 am
content: Quote from: Rasz on May 13, 2016, 08:43:22 amIf you add an additional 20% turns to the primary, they are fine.