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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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22nd Apr 2019, 6:57 pm | #21 |
Pentode
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Re: Sony KV-2912U - won't turn on - AE-1A chassis
That's a very nice list and gives me quite a few ideas, thank you very much!
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22nd Apr 2019, 8:29 pm | #22 |
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Re: Sony KV-2912U - won't turn on - AE-1A chassis
What happens if you disconnect the line output stage?
I'm wondering if the LOPT is faulty. |
23rd Apr 2019, 6:58 am | #23 |
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Re: Sony KV-2912U - won't turn on - AE-1A chassis
Yeah I'm starting to wonder the same thing. I replaced it with a brand new HR 7244 which is what was recommended but maybe it was a duff. Occasionally it will turn on as in I can hear sound but no tube activity which is what the fault was before except the tube would fire up. The other chassis I've been borrowing parts from has a good LOPT but it's a 21" tube so wasn't sure if it would work on a 29". Looks identical but as I don't have a service manual for this other one I wasn't sure if I should try it.
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23rd Apr 2019, 8:26 am | #24 |
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Re: Sony KV-2912U - won't turn on - AE-1A chassis
Is there a number on the loptx,s?
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23rd Apr 2019, 8:44 am | #25 |
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Re: Sony KV-2912U - won't turn on - AE-1A chassis
I couldn't see any but will check later. It has just dawned on me that I've been using the 25" service manual as my reference as I couldn't find the 29. Could be it's under powered but I'd expect some life in the tube?
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23rd Apr 2019, 9:36 am | #26 |
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Re: Sony KV-2912U - won't turn on - AE-1A chassis
Well the list8ng indicates it should be fine for a 21 up to 29" tube so might just be a duff.
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23rd Apr 2019, 9:42 am | #27 |
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Re: Sony KV-2912U - won't turn on - AE-1A chassis
I don't think the 21" and 29" tubes have the same scanning angle. There will be considerable differences timebase wise at least. J.
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23rd Apr 2019, 9:44 am | #28 |
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Re: Sony KV-2912U - won't turn on - AE-1A chassis
This is the listing: https://rover.ebay.com/rover/0/0/0?m...2F273107970600
I can't find reference anywhere else to HR 7244 except donburg which says it's for a 21". |
23rd Apr 2019, 10:05 am | #29 |
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Re: Sony KV-2912U - won't turn on - AE-1A chassis
What's the number on the original transformer? It should look something like 1-439-xxx-xx or maybe other numbersin the same format.
That's really the most reliable way to find a replacement. Mind you, it's not 100% certain that it's broke but at least it will be good to know whether the replacement should be expected to work or not. Also, could you confirm the model number of the TV set? There might be a letter missing. Last edited by Maarten; 23rd Apr 2019 at 10:19 am. |
23rd Apr 2019, 10:33 am | #30 |
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Re: Sony KV-2912U - won't turn on - AE-1A chassis
It's definitely KV-E2912U though the closest document I've found is here: https://www.electronica-pt.com/esque...ileinfo/34350/
A quick google search confirms it does indeed have a 1-439-416-11 which a quick google search indicates HR-7244 should replace. |
23rd Apr 2019, 11:38 am | #31 |
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Re: Sony KV-2912U - won't turn on - AE-1A chassis
I missed the letter E, so now the model number is clear and can be used to look up the transformer.
Googling something that is in front of you might not be the most accurate way to determine a part number as opposed to looking at the actual part. I checked with Aswo and they mention 1-439-416-11, -12 as originals and -51 and -52 as original replacements. Strangely, Efiter (the transformer manufacturer) gives HR7244, HR7244, HR7243 and HR7245 as replacements for those four, respectively. I think it's safe to conclude that a HR7244 should be fine in this set. Now to determine whether it and the original are indeed defective, or that there's some other fault in the set (FBT's were always blamed, it's a tradition of sorts). Maybe use a ring test? Did you test the power supply loaded with a light bulb instead of the line output stage? You say the tube 'fired up' before, do you mean you saw the heater light up? In that case the FBT was probably fine. Maybe the G2 voltage was low or missing or the vertical deflection. If the heater doesn't light up anymore, there may now be additional faults. Last edited by Maarten; 23rd Apr 2019 at 11:55 am. |
24th Apr 2019, 11:51 am | #32 |
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Re: Sony KV-2912U - won't turn on - AE-1A chassis
I'm sure there's additional faults as I don't seem to be getting 27v tested directly from the FBT.
I'm going to see what happens when I put the original FBT in. What I am getting is (while the TV thinks it's on): 27v = 0 12v = 6.5v 5v = 2 8v G2 = 52.4v H1 = 117.8v H2 = 118.1v Blue gun = 120.1v Green gun = 120v Red gun = 116v |
24th Apr 2019, 6:08 pm | #33 |
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Re: Sony KV-2912U - won't turn on - AE-1A chassis
The 27V line seems suspicious. Have you tested for shorts there? I haven't looked up the schematic yet, but isn't it used for vertical deflection?
When you say "directly from the FBT", do you mean after the respective rectifiers, or right at the physical connections of the FBT itself? |
24th Apr 2019, 8:14 pm | #34 |
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Re: Sony KV-2912U - won't turn on - AE-1A chassis
There's no 27v (well 0.02v) right at the FBT itself, let alone the VM board. Yes it is used in deflection. I was a bit concerned to see it was a dead short with ground but on my working chassis (21" AE1-C) it's the same.
Just wondering if it only outputs 27v if HV is running (which I assume it isn't)? That's the old and the new FBT that give exactly the same result so would be inclined to say it's not that. |
24th Apr 2019, 9:05 pm | #35 |
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Re: Sony KV-2912U - won't turn on - AE-1A chassis
Re:27V supply, You will get a low ohms reading to chassis there (at the FBT pin) as the other end of that winding inside the transformer is connected to chassis (via pin 11 FBT), have a look at the circuit diagram.
Another thing is you will not get any (sensible) DC reading at that point either, even if the line stage was running correctly as it is primarily a pulsed (at line rate) voltage, you need to measure the DC voltage at the associated rectifier output/smoothing capacitor (C801 +), and also as it is a lopt derived supply the line output section would need to be running correctly for this to be present. On this chassis, as it now aged and with this type of fault I would start by replacing all 4 of the Electrolytic capacitors in the primary side of the PSU, also the smoothing capacitor (another Electrolytic) for the 14 V rail on the secondary side of the PSU this time (C615), was known for giving problems years ago too. In case you are not aware Electrolytic capacitors are polarised, ie. have to be fitted the correct way round.
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25th Apr 2019, 12:29 am | #36 |
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Re: Sony KV-2912U - won't turn on - AE-1A chassis
Excellent, so I can rule out 27v as an issue in this state.
I have already changed all the electrolitics in the primary/secondary sections. Yes I'm fully aware how age and heat can affect them, polarity also but thanks for the warning anyway. Best to say it just in case. This is going to turn out to be something silly I'm betting by this point. Ive changed out most of the usual suspects if not all. |
25th Apr 2019, 3:40 am | #37 |
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Re: Sony KV-2912U - won't turn on - AE-1A chassis
You can't rule it out at this point, since the only way to take measurements is after the respective rectifier. This goes for all FBT derived DC voltages.
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25th Apr 2019, 10:14 am | #38 |
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Re: Sony KV-2912U - won't turn on - AE-1A chassis
You might check the .1 mfd or 1 mfd cap feeding the H driver tx and re-solder the pins on it too.
I found many of them bad, and they can cause the HOT xistor to fail. Please remember that on Sony, any semis should be OEM. Their sets do not respond well to universal semis. The specs on their xistors are critical to proper operation of the set. Been there & have the hat on that one. HTH |
25th Apr 2019, 10:43 am | #39 |
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Re: Sony KV-2912U - won't turn on - AE-1A chassis
I thought 27v would only be generated if HT is running?
I've now changed all electrolytics (not touched the audio section though). The list of parts changed has grown somewhat, and STILL no change at all: Q609 D601 C818 IC502 T802 C604 IC601 D612 D910 C613 PS601 + PS602 tested ok D801 C811 (2.2uf instead of 2.0uf) Q805 C825 T801 R809 Q604 (swapped for Q507, canal +blk) T602 C804 R807 D803 C605 C617 C611 C608 R831 IC501 (TEA2028B) IC604 (5v reg) Really don't want to scrap this one, it's taken me literally years to find a 29" AE-1A set and they're only getting harder to find. Thank you all for the help so far, hopefully it will yeild some results soon! |
25th Apr 2019, 11:08 am | #40 |
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Re: Sony KV-2912U - won't turn on - AE-1A chassis
Changing huge amounts of random parts seldomly works and opens up the chance of introducing new faults. I think if you want to do this repair yourself, you won't be able to fullly take advantage of troubleshooting tips an hints until we've established what you know about troubleshooting and underlying theory of electronics and what you need to know more before proceeding.
The general direction of the troubleshooting needs to be more measuring, less replacing. Two kinds of measurements are particularly useful starting out in situations like this. Measuring DC voltage (after the diode, not on the transformer pins) and measuring for shorts downstream (using diode mode on the meter). Last edited by Maarten; 25th Apr 2019 at 11:17 am. |