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-   -   Sony 8-301w no HV (http://www.videokarma.org/showthread.php?t=269743)

avalon1308 11-12-2017 01:28 PM

Sony 8-301w no HV
 
Hi All,
I have 3 set, 2 American ones and one European one, they all suffer from no HV,I have changed all the lytics in the sweep section but no difference, the horiz output transistor measures fine but gets very hot (2SC41). I do have a waveform at the collector at the correct frequency but seems to be distorted and too low.
since it is not easy to reach the components on the board, I am afraid that I will eventually break the PCB and the copper lines.
would someone happen to know if there is a common problem on all these sets. I find it strange to have the same symptoms on all of them. does the flyback transformer go on these sets, I have no means of measuring the transformer.
I would really love to have at least one of them going.
I thank you in advance for your help and advice.

dominique

timmy 11-13-2017 05:57 AM

Quote:

Originally Posted by avalon1308 (Post 3191965)
Hi All,
I have 3 set, 2 American ones and one European one, they all suffer from no HV,I have changed all the lytics in the sweep section but no difference, the horiz output transistor measures fine but gets very hot (2SC41). I do have a waveform at the collector at the correct frequency but seems to be distorted and too low.
since it is not easy to reach the components on the board, I am afraid that I will eventually break the PCB and the copper lines.
would someone happen to know if there is a common problem on all these sets. I find it strange to have the same symptoms on all of them. does the flyback transformer go on these sets, I have no means of measuring the transformer.
I would really love to have at least one of them going.
I thank you in advance for your help and advice.

dominique

I don't get into many of solid state sets but if they are old flybacks do go bad and humidity could be a cause along with resistors. Check resistor values around the horizontal transistor.

jr_tech 11-13-2017 01:15 PM

Does anybody here have a schematic for the little set? I have never seen one.

jr

tom.j.fla 11-13-2017 03:26 PM

The set is covered in SAMS #588-3 also find the schematic in the October 1961 issue of Electronic Technician you'll find it at the AMERICAN RADIO HISTORY site. Sorry I can't post a link to the magazine. Stuck with metered internet a real bummer when running at 2G :-( All the best,Tom.J

jr_tech 11-13-2017 05:46 PM

Thanks Much! :thmbsp:

I don't see any real "trouble spots" however. Are the flybacks or yokes on these sets known to be troublesome?

jr

tom.j.fla 11-13-2017 09:18 PM

Your welcome, Yoke & fly not to much trouble ring them to be sure. E-caps are Royal Pain--- though. The 1DK h.v. rectifiers were not all that great. And lastly follow the horiz. set up to the letter if you want the little beast to work AND last. Also make sure that all the plug connections are good and clean that really helps. Read Phil Nelsons' wright up on this model very informative. All the best, Tom.J

avalon1308 11-14-2017 03:15 PM

thank you for the tips, I will follow the set up of the HV section to the book and see.. I still have a few caps to change in the horiz section. I am really afraid of blowing the transistor since it gets really hot.
thank you fro your help

tom.j.fla 11-14-2017 03:27 PM

Let us know how the repair goes. All the best, Tom.J

Mr Hoover 11-16-2017 06:44 AM

I have several of these sets and never had that problem.
One did have a 2SC41 that got quite hot but changing the transistor cured it,normally they run warm to the touch but no more.
It could well be the 1DK1 eht rectifiers loading down the output stage.Try disconnecting them and see if the 2SC41 temp drops and the waveform improves.
You could think about solid state replacements for them.
Is the HV solid state diode ok on the board just along from the transformer? I had a problem with one..Again, disconnect one end and see if 2SC41 heat reduces.
Good Luck.Not the easiest sets to work on.
Hugh

avalon1308 11-16-2017 02:17 PM

you are right, not the easiest set to work on, did they ever make card extenders for those sets.
the 2SC41 is really more than warm to the touch and I don't even understand how it can take that heat. pretty robust!!!
I replaced all capacitors on the board and now I have some HV, and a white line on the top of the screen totally out of focus that varies in amplitude with the brightness control. the rectifiers are the 1DK1 (2 of them). as Mr Hoover said, they may be weak. Unfortunately, I don't have any and they seem to be hard to find. I will try disconnecting them and see if the 2SC41 gets colder. is there any solid state replacement for those HV rectifiers
thank you all

Electronic M 11-16-2017 07:13 PM

Has the thermal paste/pad on the output transistor ever been changed? Sometimes in some equipment, it will get old and stop conducting heat from the transistor to the heat sink causing the transistor to overheat. Probably not the root cause of all your problems, but it could be contributing.

jr_tech 11-16-2017 10:11 PM

Quote:

Originally Posted by avalon1308 (Post 3192131)
is there any solid state replacement for those HV rectifiers
thank you all

I used one of these in my RCA 8PT7034 to replace the 1V2 rectifier, I suspect they would work well in the 8-301.

https://www.ebay.com/itm/10-pcs-2CLG...cAAOxyV85RzIDA

not affiliated,
jr

avalon1308 11-17-2017 10:39 AM

hi, well looks like the transistor has already been replaced, there is no thermal paste, only the isolating pad.
thank you for the tip for the HV rectifier, they are cheap enough I will buy them right away.
Any idea what's the current going thru these tube rectifiers, I assume just a few mA

d

jr_tech 11-17-2017 01:16 PM

Likely less than 0.1 ma. A 1V2 is rated at 0.5 ma, A 5642, a similar but somewhat larger sub mini rectifier than the 1DK1, is rated at only 0.25 ma.

5642 & 5642S:

https://farm5.staticflickr.com/4546/...be121f_z_d.jpg

jr

tom.j.fla 11-17-2017 03:55 PM

This part is what I use to replace those sub-mini tubes in small screen television sets. Type ECG/NTE 518 specs: 10kV peak reverse volts,25mA Average Forward Current,with Forward Voltage Drop 18 volts at 25 mA. Now this part is rated for high frequency service. You most likely can find a part in your part of the world that would work. All the best, Tom.J


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