Gould 4035 shorted trsnformer  - Page 1
Forum section: electronics / testgear

author: Anks
author_rank: Frequent Contributor
timestamp: October 12, 2013, 12:33:54 pm
content: Hi my friend brought me a old Gould 4035 DSO that was working but after being on for a hour started to smoke then blew the fuse before I could traverse the mountains of crap Ive been collecting to plug the plug.Anyway Ive whittled it down to the transformer developing a short by unloading all the secondary and it still pulled way to much current. I confirmed a shorted turn using the neon bulb test.Now my issue is were do I find a transformer to replace this one. It has a 210v, 950v and a 6.3v secondary with two other center tapped windings the manual doesn't list the voltages for.I'm more concerned about were I can get a transformer for the 950 volts to the point were Ive considered using a 50 volt backwards.The scope is in really good nick and it just seems a shame to bin it. anyone got a suggestion.Cheers Kris

author: SeanB
author_rank: Super Contributor
timestamp: October 12, 2013, 01:03:10 pm
content: Rewinder is not an option? Most motor rewinders will happily do transformers as well, as a welcome change from the run of the mill induction and universal motors along with lift motors and solenoids they do each day.

author: Anks
author_rank: Frequent Contributor
timestamp: October 12, 2013, 01:11:39 pm
content: I spent ages trying to find someone local recently to rewind a Vox ac50 transformer and gave up everyone seems not to be interested in one offs. There used to be a guy in Manchester that would rewind me transformers but hes since moved on or retired. (For anyone that finds this post looking for a VOX ac50 transformer Majestic transformers is the place to go.)I'm considering rewinding the thing my self. I may only have to replace part of the secondary if its not too badly damaged. Maybe starting with a old MOT.Majestic transformers will build me a transformer but I could go buy three of these scopes for the price sadly.

author: SeanB
author_rank: Super Contributor
timestamp: October 12, 2013, 01:18:09 pm
content: If doing it yourself reuse the existing core after carefully removing the laminations and noting the original wiring connections, size and number of turns, along with the insulation on the wires and the sleeving separating the windings. Doable but does take some time. I have done motor armatures that way, rotors are a real pain though as you need to wind the loops and place them in the slots with sleeving and get them in a tight spot without damaging the insulation then place the top cover and varnish them. Transformers other than toroids though are easy with an existing former or a former you made that fits. You just count turns, add sleeving and tape and in the end varnish.

author: Anks
author_rank: Frequent Contributor
timestamp: October 12, 2013, 01:35:14 pm
content: Here is the manual it has all the schematics and if someone could take a look at the PSU and give some suggestions what else could be done before I go down the route of a rewind I'd be very grateful.

author: Anks
author_rank: Frequent Contributor
timestamp: October 12, 2013, 04:54:45 pm
content: Has anyone got a suggestion what gauge of wire I should wind these in or how to measure the old wire.

author: tautech
author_rank: Super Contributor
timestamp: October 12, 2013, 07:08:26 pm
content: Measure with a micrometer and refer to tables.http://en.wikipedia.org/wiki/Standard_wire_gaugehttp://en.wikipedia.org/wiki/American_wire_gaugeor try and find a cheapy on the net to canabilize!Good luck

author: MarkL
author_rank: Unknown
timestamp: October 14, 2013, 01:28:29 pm
content: Another approach is to substitute the old transformer with several smaller ones. There's no reason it has to be one big transformer. As long as you can get reasonably close to the original ratings, you just need the space internal to the equipment to be able to mount them.I've been able to repair a couple pieces of equipment this way that otherwise would have been very costly.The compact, flat style transformer with dual primary and dual secondary worked well for me. You can wire them up for 120/240V input, and do parallel, isolated, or center-tapped on the secondary. The Triad FP series (http://www.triadmagnetics.com/catalog_template.php?productCategoryId=66) and Hammond 229 series (http://www.hammondmfg.com/229.htm) are two examples.

author: Anks
author_rank: Frequent Contributor
timestamp: October 15, 2013, 12:01:43 pm
content: dose anyone reckon I could use a voltage tripler

author: tized
author_rank: Contributor
timestamp: October 15, 2013, 01:42:00 pm
content: Quote from: Anks on October 15, 2013, 12:01:43 pmThe 950V winding connects to a voltage doubler, so a tripler will defy the doubler which depends on AC to work.Using a transformer in revers, as you wrote in the first post, should work as long the secondary is properly insulated. Might need to get a transformer rated for a higher current to avoid core saturation.

author: Anks
author_rank: Frequent Contributor
timestamp: October 16, 2013, 03:18:40 pm
content: I was thinking I could run a transformer in reverse off a tap for the 210v I need as well or would it work better straight of the mains.

author: tized
author_rank: Contributor
timestamp: October 16, 2013, 08:02:07 pm
content: Quote from: Anks on October 16, 2013, 03:18:40 pmWorks either way, but I would keep it simple and wire directly to the mains. Make sure to get transformers with two primaries/secondaries (4-wires) so you can wire them like the original transformer, as there is probably a mains voltage selector there.

author: Unknown
author_rank: Unknown
timestamp: October 16, 2013, 10:22:03 pm
content: Would you really trust secondaries designed for isolated low voltages with mains isolation? On transformers with one bobbin or toroidal transformers, the mains winding is often on the inside, then a layer of insulation, and then the secondary. Putting mains on the secondary means that you rely on the lacquer and the wimpy insulating foil / tape (if present) for mains isolation.

author: Anks
author_rank: Frequent Contributor
timestamp: October 17, 2013, 07:00:44 am
content: Quote from: alm on October 16, 2013, 10:22:03 pmThe point the transformer is connected would be irrelevant because it will be powered off the 210v that will also depend on the voltage selector.

author: Anks
author_rank: Frequent Contributor
timestamp: December 05, 2013, 01:48:12 am
content: Well I decided that I was going to have a go at fixing this by winding a new transformer. Now after all the time this took me I should of just either knocked it on the head or done it by hand but were is the fun in that.Well I decided that I was going to build a hacked together automatic transformer winder out of bits of old printer and an abandoned lathe project I had knocking around.And here is the transformer being madesadly the scope now powers on but the digital storage and on screen cursors etc still don't work. Ive not given up on it just yet after all the time and effort Ive invested. Ive used it more as motivation to get me back doing work with micro controllers so even if it cant be fixed its served a purpose.

author: tautech
author_rank: Super Contributor
timestamp: December 05, 2013, 04:27:02 am
content: Wow! Good on you. Patience and perseverance often pays off. And we learn a lot on the way.