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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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#1 |
Hexode
Join Date: Aug 2018
Location: Dublin, Republic of Ireland.
Posts: 494
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Hi Everyone,
turning to the experts for help as im stumped.... Im working on my little Dansai Portable TV I had some vertical on it but it was squashed, After turning it on and off a couple times while testing i now have a new fault that has me stumpted, When its taken out of standby all i get is a Loud continuous screeching noise (coming from either the LOPTX or the Line Drive Transformer) after a few seconds these three capacitors C425, C424 & C420 Get Very Hot C420 is getting much hotter than the others, too hot to touch without getting burned. I've no idea whats causing this , I removed the vertical connection wires from CN401 and the set came on with Horizontal deflection working, reconnecting the wires brings the fault on again namely wire 4 it runs (soemtimes) with wire 3 connected and sometimes it doesnt. Can you guys please help me or point me in the right direction. Ive attached a picture of the vertical circuit taken from the manual. Red is the capactior thats getting the hottest, the other are in orange Its using the ART-TECH GT9313 Chassis if thats any help to anyone
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Cheers, Luke |
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#2 |
Dekatron
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,147
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Two possibles. The loud screech is the power supply overload due to a short on the 26v line. It looks as if it is derived from the lopt.
Probably due to a S/C frame output I/C or the supply diode/diodes in the 26V line. Just a thought on first checks. John. |
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#3 |
Hexode
Join Date: Aug 2018
Location: Dublin, Republic of Ireland.
Posts: 494
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Thanks John, the Supply Diode is D405, I'll change it and see what happens, Its a BYD33D so ive a few handy.
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Cheers, Luke |
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#4 |
Dekatron
Join Date: Apr 2005
Location: North Wales, UK.
Posts: 6,925
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I'd agree with John. it's odd that capacitors are overheating, and usually is due to excess voltage or ripple they can't cope with. So I'd change the diode, the three capacitors plus C434 and the IC.
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#5 |
Hexode
Join Date: Aug 2018
Location: Dublin, Republic of Ireland.
Posts: 494
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Ive changed the Diode and the screeching has stopped and the Capacitors are no longer overheating, i changed C420, i have a tiny tiny amount of vertical deflection if it runs for about 30 seconds, In the service manual C434 is listed as a 220uf 40v but fitted on the board is a 470uf 35v?
I'll have to check what i have and hopefully have the right size caps to replace them . The IC i think might be ok but ive a couple ordered anyway and will replace it just to remove all doubt about it, they should hopefully arrive tomorrow.
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Cheers, Luke |
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#6 |
Dekatron
Join Date: Apr 2005
Location: North Wales, UK.
Posts: 6,925
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Go with the 470/35v which should be ample on a 24v rail. I'd replace the others as well as they've been overheating and probably will be useless by now. These, together with a new IC should get things going again.
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#7 |
Dekatron
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 7,577
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I would also change D407 to be on the safe side. You can probably use a 1N4148 if you dont have a BAX12
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There are lots of brilliant keyboard players and then there is Rick Wakeman..... |
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#8 |
Hexode
Join Date: Aug 2018
Location: Dublin, Republic of Ireland.
Posts: 494
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I changed those Capacitors and tried it, the first two times power was applied it made that screech again but on the third time it didnt and came on (still no vertical) so im going to change the D407 (I'll have to use a 1N4148 ive no BAX12) and the IC which i ordered two of two weeks ago should hopefully arrive tomorrow
Odd that it made that noise again but only twice and then powered up, could there be something else going on that im missing?
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Cheers, Luke |
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#9 |
Dekatron
Join Date: Apr 2005
Location: North Wales, UK.
Posts: 6,925
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Change the IC first then worry!
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#10 |
Hexode
Join Date: Aug 2018
Location: Dublin, Republic of Ireland.
Posts: 494
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Hi
Replaced the IC today and same result, i have vertical but its squashed at the top with the OSD Shruken, its still tempermentle with that noise, sometimes it starts fine others it just does the screech and that capacitor gets hot again
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Cheers, Luke |
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#11 |
Dekatron
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,147
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Use the correct rectifier supply diode. It needs to be a fast switching type due to line frequency and of the correct spec for current and voltage. J.
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#12 |
Hexode
Join Date: Aug 2018
Location: Dublin, Republic of Ireland.
Posts: 494
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The BAX12A that i fitted is the same as the original and the diode on the supply line was a BYD33D and ive fitted the same. Ive also replaced every capacitor in the vertical circuit and this is the result...
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Cheers, Luke |
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#13 |
Dekatron
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,147
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The only other test would be to run the fop stage from an external variable power supply and see how it performs. J.
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#14 |
Dekatron
Join Date: Apr 2005
Location: North Wales, UK.
Posts: 6,925
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What's the voltage on the +26v line at the IC?
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#15 |
Hexode
Join Date: Aug 2018
Location: Dublin, Republic of Ireland.
Posts: 494
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Hi All
still working on this tv, i ended up changing C418 (100n) and the screeching didnt come back but still hadnt got full vertical, I noticed R419 looked a bit worse for wear even though it measured good so i changed it today. screeching is back and wont stop and that same capacitor reaching boiling point after 3-4 seconds, cant leave it powered on long enough to read the voltgage on the +26v line cause that cap will go boom, ive wasted 5 of those caps trying to get this sorted (will have to order a bunch more) im honestly lost at this point, ive changed the Vertical IC, both diodes, Every capacitor, its only the resistors i havnt changed and that screeching still wont stop. can anyone offer any more help with this, short of literally changing every component in the circuit AGAIN im lost
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Cheers, Luke |
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#16 |
Dekatron
Join Date: Apr 2012
Location: Worksop, Nottinghamshire, UK.
Posts: 5,554
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Is the scan coil glued together with that brown glue?
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#17 |
Hexode
Join Date: Aug 2018
Location: Dublin, Republic of Ireland.
Posts: 494
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Surprisingly its not
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Cheers, Luke |
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#18 |
Dekatron
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,147
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A few seconds and it's boiling hot. Most odd. What is the voltage across it? J.
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#19 |
Hexode
Join Date: Aug 2018
Location: Dublin, Republic of Ireland.
Posts: 494
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I haven't even left it on long enough to get my meter probe on it because the capacitor bulges within seconds, never let it get to the point it blows I will have to try though.
The cap that's in it now is bunched so I've ordered some new 2200u @35v, 10v higher than what's there at the moment and I'll see how they do, I've also ordered some new BYD33D for the supply diode (last time replacing this cured the blowing cap and screaming PSU albeit not for long) the Diodes arrived today just waiting on the new caps before i try them out, hopefully it returns to at least just the squashed vertical so i can do some proper voltage measurements
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Cheers, Luke |
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#20 |
Hexode
Join Date: Aug 2018
Location: Dublin, Republic of Ireland.
Posts: 494
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Probably wont be much help but heres a very short video of the sound, had i left it on 5-10 more seconds the BYD33D would be cooked and the Cap would probably go Boom not long after.
https://youtu.be/_JbRleW0AHo
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Cheers, Luke |
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