So, a fair bit of work...tomorrow evening, I will clean the chassis up a bit and test the rather sickly looking mains transformer. The fuse mounted on top of the transformer is already missing, so this investigation will be interesting.
To understand the black art of electronics is to understand witchcraft. Andrew.
Hi, well I have removed the mains transformer for testing and although fried to a crisp, it still appears to work. A secondary provides exactly 6.3 vrms (crt) plus 50-0-50 vrms using the 240v tap. An additional winding provides 190vrms with respect to neutral. I used a 60w lamp to limit any excess current if there were shorts, but there seems to be none. What has loaded the transformer I do not know as yet, but could measure no direct shorts on the lines away from the transformer.
One connection on the primary parted company from the crispy card, but is electrically ok. I may be able to repair it by replacing the cooked outer card surround.
Even if this transformer works in the set, I don't like it. It has suffered too much and you can see how burnt the insulation is on the windings themselves. I may need the services of a transformer re-wind specialist.
To understand the black art of electronics is to understand witchcraft. Andrew.
Thank goodness the transformer seems OK, I recon that would be hard to replace or expensive to rewind.
Edit crossed before your edit update, I see you're still not sure ?
Hard to replace for sure, but when you consider I paid only £22 for the set, a re-wind will be worth it. But let's re-consider this later....there is much more to investigate first.
To understand the black art of electronics is to understand witchcraft. Andrew.
The winding on the primary above the 240v tap provides 190 vrms, this goes on to provide the main HT for the set and I can't see how 190v is enough. I would have thought it was stepped up, unless I'm mistaken.
To understand the black art of electronics is to understand witchcraft. Andrew.
It never ceases to amaze me just how much punishment a transformer can survive. I remember my brother, bless 'im, lousing up the connections to his Hornby train set, and shorting out the "Train Transformer/controller" - dead short it was, and left like that for about two hours. I saw smoke belching out of every orifice, yellow wax and plastic oozing out of the vents in the bottom, and the top of transformer was far too hot to touch. The stench of burned lacquer and paxolin permeated the whole house for days after, and yet, once cooled down again that transformer went on to live another twenty odd years!
There have been other examples of tortured transformers, but that one always stands out in my mind.
My only comment would be to definitely never leave the set unattended whilst switched on and keep a close vigil on the transformer to monitor its behaviour. At least until you know its behaviours and habits. Better yet if you can, replace it, or rewind it.
Isn't the transformer connected like that considered as an auto transformer and the winding above the 240V tap should provide more than 240V with respect to neutral?
Isn't the transformer connected like that considered as an auto transformer and the winding above the 240V tap should provide more than 240V with respect to neutral?
Jon
Hi Jon,
Precisely, and I think it is way too low at 190v. Along the main smoothed HT1 line, a voltage of 280vdc is shown. It is half wave rectified too.
To understand the black art of electronics is to understand witchcraft. Andrew.
Once again, I have made a complete fool of myself. I had the primary tapping's the wrong way around and was feeding 240v INTO the top of the winding above the 240v tap.
With them correctly placed now, I have..... (240v feed to 240v tap), 230v on the 230 tap and 210 on the 210 tap with respect to neutral. On the high tap (For HT), there is 260v.
Don't forget that my secondary readings were off load, so for instance the 6.3v is now bound to be slightly higher anyway.
And to think I can make a mistake like this at this early stage !!
Shall I give up and just grow rhubarb? I'd probably grow it upside down though ?
To understand the black art of electronics is to understand witchcraft. Andrew.
Shall I give up and just grow rhubarb? I'd probably grow it upside down though ?
You'd have to come and live up here in Wakefield Andrew....The Rhubarb Triangle !
Not so; once upon a time there was a bridge in Peterborough that carried the M&GN eastwards - it, and its embankment, were known locally as Rhubarb Bridge on account of the amount of it grown there! Sadly all gone now - the A47 replaced it.
Anyway ! I'm half-way to making the transformer connections more secure and the first big can electrolytic has reformed nicely. Yes, this one with a bulge in the top, surprisingly.
To understand the black art of electronics is to understand witchcraft. Andrew.
I've finished effecting a temporary repair to the mains transformer by using terminals from a fanning strip (similar to tag-strip but with double terminals) punched through card and the lugs bent back to secure them underneath. They provide quite strong anchor points surprisingly. I have used additional card on the inside to prevent the lugs from shorting to the windings. I used sleeving on the wires as the old stuff just crumbled away, as did the original cooked card.
At least the insulation between windings is still good and there are no shorted turns, but if it fails I will have to get it re-wound as sourcing a replacement is probably hardly likely.
To understand the black art of electronics is to understand witchcraft. Andrew.
