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

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.

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

jr

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

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

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

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

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

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

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

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.

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-20KV-10mA-High-Voltage-Diode-HV-Rectifier-Tesla-Ham/272930672946?hash=item3f8bef9132:g:hMcAAOxyV85RzID A

not affiliated,
jr

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

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/4546/26709926819_09fabe121f_z_d.jpg

jr

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

https://www.tubedepot.com/products/1dk1

wow, very little current!, I will try to find these little tubes. I am going to California and Arizona tomorrow, I might be lucky there. thank you.

the tubedepot has them and also the 5246 on ebay, great help thank you!!

Keep in mind that the 5642 is likely not a direct replacement for the 1DK1... I mentioned them as an illustration of a similar tube that is rated for very low current. I can't find a data sheet for the 1DK1.

jr

thank you, I realize that, I went ahead and purchased a few 1dk1 from tubedepot.
hope they will arrive, I live in italy and many of my packages get lost in the post!!!!.

Hi, back from the US with tube rectifiers, I installed them and yes, I have HV now a lot more stable and a raster. lum is not great but could be normal on this little set. the transistor still gets really hot but seems to be taking the heat with no problem, this now showed me the next problem. I have a vertical issue, I have a straight line on top of the screen and to final stage transistor is dead cold. none of the controls have an effect although on the scope I see some variations when I move them. I might have an open resistor of an ope transistor if that is possible. when I disconnect the yoke, the line goes in the middle of the screen. will work again on it today.
good weekend to all

Shorted 500uf/12volt capacitor between the emitter of the vertical output transistor and the deflection yoke? :scratch2:

jt

Hi, I replaced all the capacitors on the board with new ones, then just replaced the 500uf again, now I have the top half of the screen lit. getting somewhere!!!, I ordered some new transistors to replace the 2sb147. I measured it but being a Ge, it measures funny and still don't know if it is good or not.
I never thought a transistor could go weak but after having replaced the one in the horiz, I had much better results with the HV and raster!?!?. I might have the same issue with the vert output transistor. They are all Ge transistor, perhaps being Ge they can go weak. would it be the case?

There are several failure modes that can weaken a transistor....I have read that there are sometimes multiple connections to the chip that are very fine gold wires, failure of one or more can weaken the performance, but the transistor will still function somewhat.
Junction leakage current can also increase with age.
Rare, but not unknown problems.

jr

Only Ge fails I remember were dead short, open or intermittent
open, & noisy ( crackling in audio). Not like Si that work or dont.
Glad Ge transistors are long gone !

For overheating HOT measure the current. SAMS schematics almost
always give the specs, someone here will help with that. You can
have a problem that does not show in the picture especially on such
an aged set.
Ge's often use complex bias with diodes & thermistors. Can be quite
hard to find problems when something is only "a little off".

Good luck
Zeno:smoke:
LFOD !

well, learning everyday!!!, not used to the Ge but they seem to take more stress than the usual Si.
I have another question, in the Horiz osc. what are the elements that decide for the frequency, I realized that it never reaches 15750 Hertz, instead, it goes extremely low (below 5kHz) making the whole circuit noisy (scary!!) and the highest frequencies I can reach in 11 to 12 kHz.
I was misled by the sams doc showing only half the frequency but at the output of the
2sc41 I surely need 15750 Hz or close to this. Am I wrong???.
I measured all elements and they are within specs unless there is a mistake in the doc.

this set is a real challenge.
thank you again for all the tips

You are measuring frequency with an oscilloscope, and not a counter correct? Counters can be VERY inaccurate on non-sinusoidal waveforms (which is what a sweep sawtooth is).

yes, I am measuring it with an oscilloscope that has a frequency counter. you are right, any kind on interference or spike will change the count.
I just read the "How important is this cap's value (Sony 8-301W)? " in this forum and learnt quite a few things on the oscillator. I will go ahead and replace the caps 98 to 101 and try to adjust L14 but still need to figure out a way to do it.
Is L13 a critical one?
thank you

Hi,

I work again on the set and measured all caps and the are spot on, only one, C98 was 10% higher than expected, still decent. I tried to tune B1 in L14 but with only little effect, max frequency 12.3kHz. I then changed C101 to 10nF instead of 20, frequency went up to 14.5kHz, changed it again to 5nF and now I have a very decent range going from 14k to way over 16kHz. The pulse at the horiz. output X20 is now very clean and steady. (before I could see some unwanted spikes). I applied a signal and I could sync it but kinda wobbly, not stable. I adjusted the horiz drive and it somehow improved it but still not OK.
I don't know if the coil L14 could be bad, if it is the case, I could take it from another set and try it. I am a bit concerned by the big difference in C101 to make work.
With C101 changed, do I also need to change C99/C100. I think C98 is outside and does not influence the frequency.
Getting somewhere!!!!
with a signal applied, it is also rather noisy. but this will be the next problem.

Perhaps the diode following the coil is bad? :scratch2:

jr

Hello,

worked again on the set,, the diodes are fine, replaced T5, no real change. I swapped the 2SB51 with one in the vertical, somehow, an improvement, the sync is much better.
I realized that all 3 controls interact a lot, sync, frequency and drive. only one thing, the picture cannot be centered properly!?!?.
I could not find the reason why I needed to change the C101 to a much lower value but so be it, I have removed the PCB so many times, I must say that although this set is very sensitive and controls must be set properly, it is somehow robust, except for the poor quality of the copper on the PCB, the rest of it is rather solid and sturdy.
thank you for all your help, now I will work on the European version, it should be similar, I don't have the schematic for that one but it is in much better shape, I have raster and only the vertical has issues, I think that changing the lytics should do it.