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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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5th Apr 2014, 11:52 pm | #21 |
Hexode
Join Date: Mar 2012
Location: Liverpool, Merseyside, UK.
Posts: 453
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Re: Ferguson (early 90s) TV Repair
You won't get a reading on the ESR meter on that 14.4nF, the capacitance meter is indicating the correct value so it should be ok. The line output transistor also sounds ok from the readings you got, which could be a good sign. As someone has mentioned it is suggesting a possible short-circuit on one of the secondary supplies, likewise the possible dry joints.
Does your meter have a continuity test (audible preferably)? It might be worth doing a quick test on the diodes on the secondaries, plus any low value fusible resistors supplying them. You could do this test from each LT supply to chassis ground as well. If you get a bleep it may indicate a short-circuit on that rail, an open fusible resistor will also point to the likely area. Not totally conclusive as some diodes have a very low forward resistance but this is usually encountered in more modern circuitry. It is stabbing blind without any knowledge of the circuit or what to expect. I would certainly google your chassis and check any noted faults and causes in case it's well known first. |
6th Apr 2014, 12:01 am | #22 |
Nonode
Join Date: Mar 2010
Location: Sunderland, Tyne and Wear, UK.
Posts: 2,473
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Re: Ferguson (early 90s) TV Repair
One of the difficulties in servicing this chassis, in common with most other Thomson designed chassis, is the various comprehensive protection circuits.
On this chassis there is a "security signal" which is lopt derived and this feeds back to the main micro, if the line output section is abnormal/not running then the micro forces the PSU and set into standby. This is only one of the protection schemes on this chassis, there are others such as overcurrent and over/under voltage protections, both on the primary and secondary of the chopper supply, as well as X-ray protect etc..etc.. Thomson sets are not exactly known to be "engineer friendly" and frequently posed problems for seasoned engineers, and for a novice virtually impossible, unless it is a known stock fault.
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7th Apr 2014, 2:42 pm | #23 |
Dekatron
Join Date: Aug 2006
Location: Madrid, Spain / Wirral, UK
Posts: 7,484
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Re: Ferguson (early 90s) TV Repair
From my notes;
Initial rustle of high voltage then nothing, goes to standby, same with remote or front panel controls -R12 burnt out (0.22ohms), replacing this plus the IC01 vertical IC (TDA8177) got set working. NB: also check D01 for shorts. NB. If after replacing parts the set still appears to be tripping, try switching the set on with the remote control. The micro seems to remember the tripping state, the remote control re-sets it.
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8th Apr 2014, 12:08 am | #24 |
Tetrode
Join Date: Feb 2007
Location: Fordingbridge, Hampshire, UK.
Posts: 56
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Re: Ferguson (early 90s) TV Repair
Unfortunatly not had a chance to power up the circuit board yet though I hope to do so in the next few days. Meantime I've been trying to check some of the diodes out, though they all seem to read ok.
One however (DP13) read 100 ohms both ways though I guess that could be because it is in circuit. I did check for R12 but could not find it; there is however an RF12 which reads 2.4 Ohms and which seems to be ok, dosen't appear to be burnt out. None of the components on the board appear to be burnt out. BTW cannot seem to find D01 maybe it is something like DF01? I will remember about the remote control when I power it on. When it was last plugged in I did try turning it on with both the buttons on the front and the remote so sadly that doesn't seem to be the cause of the problem, but I wouldn't have known that for when I do try to turn it on again. ljones |