|
Hints, Tips and Solutions (Do NOT post requests for help here) If you have any useful general hints and tips for vintage technology repair and restoration, please share them here. PLEASE DO NOT POST REQUESTS FOR HELP HERE! |
|
Thread Tools |
19th Jan 2020, 2:14 pm | #1 |
Hexode
Join Date: Sep 2003
Location: Cheltenham, Gloucestershire, UK.
Posts: 298
|
Unusual intermittent fault cured
A small Japanese receiver, caseless, was in a box of 'assorted wrecks' I bought from a Radiophile auction some time ago. Before dismantling it, I thought I'd see if it was still functional. A few basics (battery, speaker, Deoxit on the volume control) allowed it to show signs of life (after the electrolytics had re-formed). But there was an annoying intermittent 'dying' effect, apparently caused by any slight movement. Obviously a loose connexion - battery snaps, vol control, solder joint gone off, etc.
A lot of searching, prodding, resoldering produced nothing. And then I noticed that the ferrite rod was expecially sensitive; yet its litz wires were soldered nicely in place with plenty of wiggle room. Then the penny dropped - the winding was resting on the volume control, and a sharp edge on the latter must be cutting thru' the litz insulation (see photo). A bit of judiciously-place insulating tape solved it.
__________________
Dave Teague |
19th Jan 2020, 2:52 pm | #2 |
Guest
Posts: n/a
|
Re: Unusual intermittent cured
I love fixes like this, I store the info in my head so when designing something I don't fall into the same trap.
|
19th Jan 2020, 5:37 pm | #3 |
Heptode
Join Date: Apr 2016
Location: Cheltenham, Gloucestershire, UK.
Posts: 875
|
Re: Unusual intermittent fault cured
Tut! Tut! Not like you to miss that Dave! (I'll have to pop 'round and supervise you a bit more often!!)
__________________
Red to red, black to black. Throw the switch and stand well back! |
19th Jan 2020, 6:06 pm | #4 |
Dekatron
Join Date: Sep 2011
Location: Rugeley, Staffordshire, UK.
Posts: 8,835
|
Re: Unusual intermittent fault cured
'like'.
__________________
A digital radio is the latest thing, but a vintage wireless is forever.. |
19th Jan 2020, 7:36 pm | #5 |
Nonode
Join Date: Dec 2012
Location: Stockport, Greater Manchester, UK.
Posts: 2,117
|
Re: Unusual intermittent fault cured
This is spooky - about a year ago there was yet another thread about replacing Ge devices with Si and I looked for a scrap simple set to take some measurements, and in a box of 'assorted wrecks' there was the PCB from an unknown Japanese pocket portable with no case which I had found years ago. An early 6-transistor 'AM-only' set with transformer-coupled push-pull audio output for speaker or earphone. Exactly like yours Dave. The only indication of brand or model was the legend SRV-62 on the tuning knob.
I'd not done any repairs for so long that I needed to ramp up my practice, starting on something very simple, like this. Applied 9V and clicked the volume control 'on' - dead short. Fair enough, I was expecting some leakage on those 60-year old electrolytics and maybe the O-P transistors so I started pulling them out. Still dead short. The supply line goes only to an electrolytic, the oscillator coil, and some resistors, so I pulled out the coil/transformer and checked for shorts to the can. None. Beginning to despair I put an ohmmeter across the supply line, it was virtually O/C - until the vol ctrl switch was clicked 'on'. 'How did that happen' you might ask (well I did) so by cutting tracks in the supply line it turns out that the switch shorts to the track earthy end when on. The bits went in a box for another day. Let's compare our two boards
__________________
- Julian It's good here |
19th Jan 2020, 11:59 pm | #6 | |
Hexode
Join Date: Sep 2003
Location: Cheltenham, Gloucestershire, UK.
Posts: 298
|
Re: Unusual intermittent fault cured
Quote:
You're most welcome Tractionist! The teapot's always full (even though the biscuit tin may not be).
__________________
Dave Teague |
|
20th Jan 2020, 12:04 am | #7 |
Hexode
Join Date: Sep 2003
Location: Cheltenham, Gloucestershire, UK.
Posts: 298
|
Re: Unusual intermittent fault cured
As you say, uncanny - but I think that they're actually different models (but with a certain 'family likeness ) In mine: there's a gap between the tuning cap and the first IFT; in yours there isn't. But both fail in having the tuning coil almost/actually resting on the volume control & on-off switch.
__________________
Dave Teague |
20th Jan 2020, 11:13 am | #8 |
Dekatron
Join Date: Aug 2007
Location: W.Butterwick, near Doncaster UK.
Posts: 8,935
|
Re: Unusual intermittent fault cured
Good one.
__________________
G8JET BVWS Archivist and Member V.M.A.R.S |
20th Jan 2020, 12:07 pm | #9 |
Octode
Join Date: Mar 2016
Location: Knutsford, Cheshire, UK.
Posts: 1,500
|
Re: Unusual intermittent fault cured
Well done for finding the fault, they are sometimes far from obvious!
My most perplexing fault was a bad pcb track whick looked OK but measured several K ohms.. upon close inspection it had a spot of mild discolouration - something attacked the copper - of course, a simple wire link fixed it.
__________________
...where on earth did that spring/screw go?? |