Sony TV9 poor on VHF - cogging - UK Vintage Radio Repair and Restoration Discussion Forum

peter_scott · 4th Apr 2005, 12:32 pm

I've just acquired a Sony TV9-90UB and am hoping you will be able to
educate me on its quirks:

1. I have a copy of the Trader service sheet and also the R&TS info, both
for the TV9-306UB. Am I right in thinking that the 306 and the 90 use the
same schematic? If not does anyone have data for the 90UB?

2. Performance on UHF is quite acceptable but VHF has a distinct lack of black level control. I guess it is a bit easier to control agc with negative modulation but I'd like to know if my set is singularly deficient. Any white object has strong black bands left and right whilst other dark picture areas are mid grey.

Looking at the 306UB schematic there doesn't appear to be any difference
in the video circuitry down stream of the detector. My guess is that the agc
on VHF just has far too short a time constant. Any thoughts? Am I missing some clamping somewhere?

Thanks,

Peter

ukcol · 4th Apr 2005, 5:34 pm

Hi Peter,

It was quite common in sets of this period to couple the video signal to the CRT via a capacitor, thus throwing away the DC component. This was done to simplify design and keep down costs by making the EHT load more or less constant. The presence of this capacitor also degrades the low frequency responce, hence the streaking

If you look on the Trader diagram for the TV9-306UB, C504 does the job in this set.

peter_scott · 4th Apr 2005, 6:22 pm

Hi Colin,

Thanks for your interest but the problem I'm describing is only unacceptable
when using the VHF tuner. If I use UHF, whether on 625 or 405 line pictures,
then there is very little to complain about. Given that after the video detector
there is nothing (that I can see) that changes between VHF and UHF modes then it would seem that my problem must reside at or before the detector.

I grant you that there is still a small amount of streaking on bright objects
using UHF and I agree this is most probably due to the a.c. coupling that
you refer to but it's not the same problem that occurs on VHF only.

Please keep thinking...

Thanks,

Peter.

flyback · 4th Apr 2005, 7:43 pm

Hi All,

The TV9-90UB is not at all like the TV9-306UB, the TV90-90UB is all transistor (bar the CRT!) and has a very diiferent AGC system.

The TV9-90UB has one video detector with a phase splitter/inverter stage following it, this is AC coupled into the video output stage with AC coupling to the CRT. (Black level..what black level!)

There is a DC resoration stage (a diode, D501) just before the video output stage also feeding the sync separator, not sure why they bothered but it's there. (as they AC couple from it!)

The AGC system does not change much between line standards but it does have its own detector and buffer.

I have seen these sets give problems when used with a modulator, although off air 625 line performance was OK.
On VHF 405-line the pictures had poor sync, frame roll and a banded look to the picture.
I investigated this and found that the vision detector was getting swamped, with the syncs getting crushed, even when the signal was attenuated down to the point where noise was showing.

My conclusion was that the set didn't like a double sideband signal!.

Never got to the bottom of the problem, working on one of these sets is not a pleasure, something to be avoided at all costs, lots of wires to fall off, tin covers to remove and the whole range of screw sizes thrown in for good measure. (eeeugh!)

The Circuit is in 'Radio and Television Servicing' 1970-71 page 380.

Malcolm

Panrock · 4th Apr 2005, 8:37 pm

Malcolm,

Thanks for the in-depth account. I've got one of these sets too - the result of a cut-and-shut job from two sets bought in from Ebay: one a non-worker with a good cabinet and bits and the other rough, with working insides.

I'd never seen the circuit. Now I understand why it line-cogs on Test Card C at anything resembling a decent signal level.

I take your point about this set being a horror to open up. I made the mistake of tampering with the springy push-pull on/off switch too. Never got it together again - replaced it with one from the other set.

I don't have this late edition of Radio & TV Servicing, so yes - please let us know when you put a .pdf up

Steve

peter_scott · 4th Apr 2005, 8:43 pm

Quote:

Originally Posted by flyback

Hi All,

The TV9-90UB is not at all like the TV9-306UB,

Never got to the bottom of the problem, working on one of these sets is not a pleasure, something to be avoided at all costs, lots of wires to fall off, tin covers to remove and the whole range of screw sizes thrown in for good measure. (eeeugh!)

The Circuit is in 'Radio and Television Servicing' 1970-71 page 380.
I do not have it as a PDF yet, if needed I will scan it to a PDF and post a link later..

Malcolm

Hi Malcolm,

I did delve inside hoping that the assemblies would look like those on
the 306 info and of course discovered as you have confirmed, that they
had at the very least been re-layed out and yes, your impressions of the
set's servicabilty are exactly what hit me too.

Your general comments are interesting. Frame sync does seem erratic
at times.

I don't have any R&TS after 1969. I'll go and see what our public library has before asking your for scans, but I appreciate the offer. The library used to have a fairly complete set. I'll think some more on your comments once
I see the schematics.

Many thanks,

Peter.

flyback · 5th Apr 2005, 3:21 am

Hi All...

I have done battle with XP, HP and Acrobat...and the result is here...

http://www.domino405.co.uk/documents/Sony_TV9_90UB.pdf

Not the smallest file (1MB ish) but thats what broadband is for!

Malcolm

Three attempts to get it like it is, Duke Nukem (Jon) and Paul Stenning must have a lot of patience!.

oldeurope · 5th Apr 2005, 8:07 am

Good morning

Thanks for the schematic Malcolm.
Peter I think C234 can cause your problem.
Please replace it by a 47uF 16V.
It is located above the VHF input at page 382.

Kind regards
Darius

peter_scott · 5th Apr 2005, 9:51 am

Malcolm,

I'm very impressed with the service and very grateful. I had looked up our local library on-line catalogue last night and of course discovered that I was living in the past. Clearly nobody is going to want repair information for radios and televisions greater than 10 years old or maybe me and the other half dozen nutters here in Edinburgh just weren't accessing the books enough in recent times. Well, for whatever reason that nice row of maroon coloured volumes in no longer available.

Many thanks.

Likewise to Darius. Thanks for the C234 suggestion and all before breakfast too. Well done guys.

Kind regards to both,

Peter.

peter_scott · 5th Apr 2005, 11:35 am

Quote:

Originally Posted by flyback

Hi All,

The TV9-90UB is not at all like the TV9-306UB, the TV90-90UB is all transistor (bar the CRT!) and has a very diiferent AGC system.

The TV9-90UB has one video detector with a phase splitter/inverter stage following it, this is AC coupled into the video output stage with AC coupling to the CRT. (Black level..what black level!)

There is a DC resoration stage (a diode, D501) just before the video output stage also feeding the sync separator, not sure why they bothered but it's there. (as they AC couple from it!)

The AGC system does not change much between line standards but it does have its own detector and buffer.

Malcolm

Hi Malcolm,

Yes, they really have redesigned quite a lot between 306 and 90. ' Must have brought in a new guy.

As in the 306 there doesn't appear to be much in the video path to explain
the problem. Perhaps something at the trap following VID DRV 1?

Darius' C234 suggestion certainly sounds good.

I guess I'll have to pluck up courage now and get my great mits into the knitting.

Thanks again.

Peter.

peter_scott · 6th Apr 2005, 11:11 am

Quote:

Originally Posted by Panrock

Malcolm,

I've got one of these sets too - .

I'd never seen the circuit. Now I understand why it line-cogs on Test Card C at anything resembling a decent signal level.

Steve

Hi Steve,

If it's easy for you to do could you take a look at your TV9-90 and see
if its performance is similar to mine? I've included three images, all using
405 lines but this probably doesn't matter. The UHF one looks reasonable.
the VHF with a low aerial signal isn't good and the VHF with high signal
(about 15dB higher) is abysmal.

Thanks,

Peter.

oldeurope · 6th Apr 2005, 11:24 am

Hi Peter,
did you replace C234?

Darius

peter_scott · 6th Apr 2005, 11:45 am

Hi Darius,

No, not yet. When I went inside for an initial look I found that the UHF
tuner knob had 180 degrees of its shaft broken at the circlip so I'm living
on borrowed time with the remaining 180 and replacing the knob was a
stressful operation. Given that, I would like to know if my set's performance
is just par for the course before I decide to risk a complete breakage of the knob.

Peter.

4th Apr 2005, 12:32 pm	#1
peter_scott Dekatron Join Date: May 2003 Location: Edinburgh, UK. Posts: 3,274	Sony TV9 poor on VHF - cogging I've just acquired a Sony TV9-90UB and am hoping you will be able to educate me on its quirks: 1. I have a copy of the Trader service sheet and also the R&TS info, both for the TV9-306UB. Am I right in thinking that the 306 and the 90 use the same schematic? If not does anyone have data for the 90UB? 2. Performance on UHF is quite acceptable but VHF has a distinct lack of black level control. I guess it is a bit easier to control agc with negative modulation but I'd like to know if my set is singularly deficient. Any white object has strong black bands left and right whilst other dark picture areas are mid grey. Looking at the 306UB schematic there doesn't appear to be any difference in the video circuitry down stream of the detector. My guess is that the agc on VHF just has far too short a time constant. Any thoughts? Am I missing some clamping somewhere? Thanks, Peter

4th Apr 2005, 5:34 pm	#2
ukcol Rest in Peace Join Date: May 2003 Location: Harlaxton, Lincolnshire, UK. Posts: 3,944	Re: Questions re Sony TV9 Hi Peter, It was quite common in sets of this period to couple the video signal to the CRT via a capacitor, thus throwing away the DC component. This was done to simplify design and keep down costs by making the EHT load more or less constant. The presence of this capacitor also degrades the low frequency responce, hence the streaking If you look on the Trader diagram for the TV9-306UB, C504 does the job in this set.

4th Apr 2005, 6:22 pm	#3
peter_scott Dekatron Join Date: May 2003 Location: Edinburgh, UK. Posts: 3,274	Re: Questions re Sony TV9 Hi Colin, Thanks for your interest but the problem I'm describing is only unacceptable when using the VHF tuner. If I use UHF, whether on 625 or 405 line pictures, then there is very little to complain about. Given that after the video detector there is nothing (that I can see) that changes between VHF and UHF modes then it would seem that my problem must reside at or before the detector. I grant you that there is still a small amount of streaking on bright objects using UHF and I agree this is most probably due to the a.c. coupling that you refer to but it's not the same problem that occurs on VHF only. Please keep thinking... Thanks, Peter.

4th Apr 2005, 7:43 pm	#4
flyback Retired Dormant Member Join Date: Apr 2003 Location: Swindon Wiltshire Posts: 26	Re: Questions re Sony TV9 Hi All, The TV9-90UB is not at all like the TV9-306UB, the TV90-90UB is all transistor (bar the CRT!) and has a very diiferent AGC system. The TV9-90UB has one video detector with a phase splitter/inverter stage following it, this is AC coupled into the video output stage with AC coupling to the CRT. (Black level..what black level!) There is a DC resoration stage (a diode, D501) just before the video output stage also feeding the sync separator, not sure why they bothered but it's there. (as they AC couple from it!) The AGC system does not change much between line standards but it does have its own detector and buffer. I have seen these sets give problems when used with a modulator, although off air 625 line performance was OK. On VHF 405-line the pictures had poor sync, frame roll and a banded look to the picture. I investigated this and found that the vision detector was getting swamped, with the syncs getting crushed, even when the signal was attenuated down to the point where noise was showing. My conclusion was that the set didn't like a double sideband signal!. Never got to the bottom of the problem, working on one of these sets is not a pleasure, something to be avoided at all costs, lots of wires to fall off, tin covers to remove and the whole range of screw sizes thrown in for good measure. (eeeugh!) The Circuit is in 'Radio and Television Servicing' 1970-71 page 380. Malcolm Last edited by Mike Phelan; 19th Jun 2007 at 11:58 am. Reason: Tidy-up for archive

4th Apr 2005, 8:37 pm	#5
Panrock Nonode Join Date: Feb 2005 Location: Worcestershire, UK. Posts: 2,533	Re: Questions re Sony TV9 Malcolm, Thanks for the in-depth account. I've got one of these sets too - the result of a cut-and-shut job from two sets bought in from Ebay: one a non-worker with a good cabinet and bits and the other rough, with working insides. I'd never seen the circuit. Now I understand why it line-cogs on Test Card C at anything resembling a decent signal level. I take your point about this set being a horror to open up. I made the mistake of tampering with the springy push-pull on/off switch too. Never got it together again - replaced it with one from the other set. I don't have this late edition of Radio & TV Servicing, so yes - please let us know when you put a .pdf up Steve

5th Apr 2005, 3:21 am	#7
flyback Retired Dormant Member Join Date: Apr 2003 Location: Swindon Wiltshire Posts: 26	Re: Questions re Sony TV9 Hi All... I have done battle with XP, HP and Acrobat...and the result is here... http://www.domino405.co.uk/documents/Sony_TV9_90UB.pdf Not the smallest file (1MB ish) but thats what broadband is for! Malcolm Three attempts to get it like it is, Duke Nukem (Jon) and Paul Stenning must have a lot of patience!.

5th Apr 2005, 8:07 am	#8
oldeurope Retired Dormant Member Join Date: Dec 2003 Location: Solingen, Germany Posts: 727	Re: Questions re Sony TV9 Good morning Thanks for the schematic Malcolm. Peter I think C234 can cause your problem. Please replace it by a 47uF 16V. It is located above the VHF input at page 382. Kind regards Darius

5th Apr 2005, 9:51 am	#9
peter_scott Dekatron Join Date: May 2003 Location: Edinburgh, UK. Posts: 3,274	Re: Questions re Sony TV9 Malcolm, I'm very impressed with the service and very grateful. I had looked up our local library on-line catalogue last night and of course discovered that I was living in the past. Clearly nobody is going to want repair information for radios and televisions greater than 10 years old or maybe me and the other half dozen nutters here in Edinburgh just weren't accessing the books enough in recent times. Well, for whatever reason that nice row of maroon coloured volumes in no longer available. Many thanks. Likewise to Darius. Thanks for the C234 suggestion and all before breakfast too. Well done guys. Kind regards to both, Peter.

6th Apr 2005, 11:24 am	#12
oldeurope Retired Dormant Member Join Date: Dec 2003 Location: Solingen, Germany Posts: 727	Re: Questions re Sony TV9 Hi Peter, did you replace C234? Darius

6th Apr 2005, 11:45 am	#13
peter_scott Dekatron Join Date: May 2003 Location: Edinburgh, UK. Posts: 3,274	Re: Questions re Sony TV9 Hi Darius, No, not yet. When I went inside for an initial look I found that the UHF tuner knob had 180 degrees of its shaft broken at the circlip so I'm living on borrowed time with the remaining 180 and replacing the knob was a stressful operation. Given that, I would like to know if my set's performance is just par for the course before I decide to risk a complete breakage of the knob. Peter.