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1974 22" Ultra 6714: Thorn 3500 chassis

 
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1974 22" Ultra 6714: Thorn 3500 chassis

Post by crustytv » Sun Sep 04, 2016 3:23 pm

Today feeling a little bored and not really knowing what to do or what to have a stab at, I thought lets have a look at the yucky old Ultra and give it the first baseline evaluation. Well it has been a while since I had a Thorn on the bench and I know how some of you just love them so don't all groan at once :qq1

Here we go, I bought this set back in April along with an HMV 2725 and other than a quick peak inside to see the cobwebs, live spiders, gnawed front edge and mouse puke balls, pretty much left it to one side. That description should at least paint a picture that this set has seen better days but I've had worse on the bench.

ultra6714-02.jpg
The Ultra 6714, quite a fine looking set though nothing special. Once cleaned and the mouse gnawing fixed should be a fairly simple with filler and dye.

ultra6714-03.jpg
The user control panel

ultra6714-01.jpg
Cob webs dust and dirt but not too bad

ultra6714-09.jpg

ultra6714-14.jpg
Mr mouse was hungry

ultra6714-15.jpg
Then he went and puked it up, sure I caught a glimpse of him in there, somewhere or did I imagine it.

The various modules look to be in fairly good condition with the PSU module looking a little on the tired side but I've had worse.

ultra6714-05.jpg
The PSU

ultra6714-06.jpg
C607 has seen better days


The Ultra's PSU module outwardly looks fairly OK, the most obvious first problem to address before power up is C607, this is in the 30V supply, no 30V rail means no 'Chopper' drive therefore no 'EHT', no 'Field scan' or 'sound' So the three rails 240V, 30V and 58-65V will all need to be checked out and to do this rather than using the set I use my Thorn test rig.

I guess on the 3000/3500 the single most troublesome module is the PSU, I've had no end of fun with these and having repaired four of them so far this year, I'm starting to get to grips with them as you can follow over here. In fact I've spent so much time working on Thorn PSU modules I have a dedicated work bench with the test rig, relevant data plastered on the back wall and parts all to hand.

ultra6714-07.jpg
The Thorn workstation


First job then is C607 but before I did that I wanted to see what the A56 120X is like and OH dear! what a disappointment. First of all I could hardly set the Cut-Off for the red gun, only managing to raise it to the required +1 division by having the G2 control at maximum rotation. Green and Blue Cut-off's were set normally. When emission tested well what can I say other than its pants!

ultra6714-08.jpg
First test of the A56-120X..... Holy Fudge Cakes!! That ain't good!

I left it running on the B&K for an hour and then rechecked Reds Cut-Off, there was a slight improvement but very minor. The emission did not improve whatsoever. Next I tried clean and balance, this restored Red and blue but Green was having none of it.

ultra6714-11.jpg
After a clean and balance, Green not playing ball

So the only option open to me now was a rejuvenate of the Green gun. This achieved the desired result giving Green the lifty that was needed.

ultra6714-12.jpg
Green given a more aggressive rejuvenate and responds well.

Well at least the repair is now viable and I should get something decent from the A56 120X. That's as far as I've got this morning, later this afternoon will see C607 replaced and then the PSU module loaded on to the test rig for first power application. Then the fun and games will truly start and as I said at the start I do apologise to those that are sick and tired of my Thorn 3000/3500 set repairs.

 
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Re: 1974 22" Ultra 6714: Thorn 3500 chassis

Post by Red_to_Black » Sun Sep 04, 2016 4:12 pm

I never get sick and tired of the repair threads :bba , Thorn or otherwise :aad

ttt: :cca

 
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Re: 1974 22" Ultra 6714: Thorn 3500 chassis

Post by marc » Sun Sep 04, 2016 5:03 pm

Red to black wrote:I never get sick and tired of the repair threads :bba , Thorn or otherwise :aad

Me too, it's always nice to see you at the bench for another "Crusty Telly Tail" ttt:

Marc.

 
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Re: 1974 22" Ultra 6714: Thorn 3500 chassis

Post by Cathovisor » Sun Sep 04, 2016 5:40 pm

And me... although (with apologies to Jeanette Winterson) Thorns Are Not The Only Televisions... :aaj

 
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Re: 1974 22" Ultra 6714: Thorn 3500 chassis

Post by Tazman1966 » Sun Sep 04, 2016 5:51 pm

Maybe this will be the inspiration for me to get back in the workshop after such a long time out of it....

 
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Re: 1974 22" Ultra 6714: Thorn 3500 chassis

Post by crustytv » Sun Sep 04, 2016 6:01 pm

It would seem during the life cycle of the 3000 series chassis, C607 underwent a number of value changes. I've found 1000uF 50V, 1250uF 63V and 1500uF 63V in this position on various PSU modules. I would hazard a guess this one was a hurried service call to a customers house, as the connections have another snipped caps tabs tacked to the others. Not a nice neat mechanical joint you as you would prefer but I guess needs must when you busy field engineer with a call card stacked to the brim to get through. However this also made it really easy to desolder and remove.

c607-1.jpg
Tags from a previous cap still visible and just tacked to this cap

c607-2.jpg
Well they came away dead easy

The one fitted here is 1000uF 63V and it has to be the worst one I've ever come across. Just look at the poor thing, don't you just feel sorry for it? You can just see it had enough, " No more please!" :qq1

c607-3.jpg
Yeee Gadds That's a funky shape, Like in clouds I could see a face

sad cap.jpg
See... You can even see his furrowed brow

Out of interest and perverse pleasure I wanted to see just how sickly it was, so on to the torture table reformer. I was quite surprised and had huge admiration for the little thing, it happily held 50V without any sign of leakage. Hang on though the cap is rated at 63V and I normally always go 10-15% above. On to the next range and the little old cap soldiered on but above 50V and just shy of 70V, it couldn't help itself and incontinence set in. All just a bit of fun!

c607-4.jpg
Leakage

I have some replacements in stock so in with a new one then up on the rig for the next instalment.

p.s. anyone spotted Micky? Sure I've seem the little git scampering about somewhere especially when I was taking some of these snaps inno:

 
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Re: 1974 22" Ultra 6714: Thorn 3500 chassis

Post by jayceebee » Sun Sep 04, 2016 6:29 pm

Never seen a Lorlin 1000uf go like that before, looks like it has Acne or worse. Has the spare connector on the mains transformer been used to "boost" the CRT heater volts?

John.

 
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Re: 1974 22" Ultra 6714: Thorn 3500 chassis

Post by Red_to_Black » Sun Sep 04, 2016 6:31 pm

CrustyTV wrote:p.s. anyone spotted Micky? Sure I've seem the little git scampering about somewhere especially when I was taking some of these snaps inno:


Certainly have :qq1 :aad

 
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Re: 1974 22" Ultra 6714: Thorn 3500 chassis

Post by crustytv » Sun Sep 04, 2016 6:56 pm

jayceebee wrote:Has the spare connector on the mains transformer been used to "boost" the CRT heater volts?

John.

Hi John,

yes I forgot to mention that. When I found the CRT was so shot I had a look at the transformer, low and behold the Orng/Brown had been transferred to the boost tap. Now I've tended to the CRT the wire was put back to where it should be.

 
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Re: 1974 22" Ultra 6714: Thorn 3500 chassis

Post by Cathovisor » Sun Sep 04, 2016 7:11 pm

I have *never* seen an electrolytic go like that before - ever!

 
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Re: 1974 22" Ultra 6714: Thorn 3500 chassis

Post by crustytv » Sun Sep 04, 2016 7:38 pm

Not made it to the rig yet, found another casualty, this being the Dynamic trip X601, a Mullard VA1040. So to get to X601 to replace I'm going to have to do the usual spatch-cocking of the PSU module.

ps1.jpg
A bit of work has taken place on this side too with a few tacked components but mostly the originals are still present.

trip.jpg
Mullard VA1040, notice the trip pre-set has been tampered with too

 
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Re: 1974 22" Ultra 6714: Thorn 3500 chassis

Post by crustytv » Sun Sep 04, 2016 8:14 pm

The PSU is spatch-cocked, on the rig ready for the C607 and X601 replacement.. A pause in the proceedings as I'm searching the stores for a VA1040, I know I've got one but typically I can't find it. :ccb

spatch.jpg

 
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Re: 1974 22" Ultra 6714: Thorn 3500 chassis

Post by Lloyd » Sun Sep 04, 2016 8:17 pm

Hi Chris,

That's a nice set you have there! I had the dynamic trip thermistor go like that on mine too, I did buy some replacements off ebay, and I'm sure I've got 1 spare hidden in the back of the set! In my impatience I measured the remains of the thermistor at about 100 ohms, so tacked in a 100 ohm wire-wound resistor. The set worked fine with it like that until the replacements arrived.

I have seen electrolytic caps go like that before, I think I have some in my junk pile.

Oh, careful of that mouse, they get in the walls and before you know it there's thousands of them!!

Regards,
Lloyd.

 
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Re: 1974 22" Ultra 6714: Thorn 3500 chassis

Post by crustytv » Sun Sep 04, 2016 8:35 pm

Lloyd wrote:.......thermistor................. I did buy some replacements off ebay

Do you still have the vendor name or what the search criteria is for on e-bay?

 
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Re: 1974 22" Ultra 6714: Thorn 3500 chassis

Post by rob t » Sun Sep 04, 2016 9:17 pm


 
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Re: 1974 22" Ultra 6714: Thorn 3500 chassis

Post by crustytv » Sun Sep 04, 2016 9:26 pm

Hi Rob,

Thanks for the link, very odd site though, it gives the price but there does not appear to be any way to purchase items. Found the spec for the VA1040 in the Mullard manual.

Va1040.jpg

 
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Re: 1974 22" Ultra 6714: Thorn 3500 chassis

Post by crustytv » Sun Sep 04, 2016 10:44 pm

I need to order some VA1040 thermistors ( or equiv's) as I appear to have zero stock. I found a donor from my one and only scrap module, it looks OK so should suffice for the purposes of diagnosing the Ultras power supply. I've also replaced C607.

Hooked up all the extension leads in the rig and powered up. Observing the rail indicators 6.3V came up, 30V came up and the 58-65V appeared. This all happened in about 1.5 seconds before the rigs trip operated ( same as the type in the 3k set) with a puff of the magic smoke appearing from R609.

With R609 (15R) overheating we have many possibilities and I need to check them all starting with the Chopper transistor (VT604) as it could be short-circuit. Then I need to check W606,W609, W616, W620 for open-circuit. There's the Crowbar SCR W621 and the 72V zener W617 either of these could be short-circuit. The Feedback amplifier VT608 could be faulty causing the mark-space ratio of the monostable to allow the 58V to 65V rail to increase above the strike voltage of W617. Not forgetting the possibility of the Mica washer on chopper transistor having failed.

Fair old bit to be getting on with there and that will be for tomorrow now.

PSU-pwr-1.jpg
Well we're on the rig and the magic smoke has escaped.

 
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Re: 1974 22" Ultra 6714: Thorn 3500 chassis

Post by Red_to_Black » Sun Sep 04, 2016 10:50 pm

You are getting a dab hand at these now Chris :elc:
I remember your first one :qq1 :bba

 
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Re: 1974 22" Ultra 6714: Thorn 3500 chassis

Post by Lloyd » Sun Sep 04, 2016 11:30 pm

CrustyTV wrote:
Lloyd wrote:.......thermistor................. I did buy some replacements off ebay

Do you still have the vendor name or what the search criteria is for on e-bay?


Yes, I've found it in my emails (that I never seem to clear out...), I can't believe it was actually back in September 2009 I bought them!

The seller name was 'dialelec', and the title of the listing was '1 bag of 2 Thermistor 61011131 VA1040 Mullard #2260'

Unfortunately, searching eBay with any of that now draws up nothing for me, also the link to their shop from the old email doesn't work.

BUT....

After a bit of searching through my eBay feedback, I have managed to find the seller! They are now 'dialelectronicsltd', http://www.ebay.co.uk/usr/dialelectronicsltd. Might be worth dropping them a message to see if they have any left? Doesn't look like they have been up to much recently from their feedback and items for sale completed listings. I have an address for them if its any use?

Regards,
Lloyd.

 
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Re: 1974 22" Ultra 6714: Thorn 3500 chassis

Post by crustytv » Mon Sep 05, 2016 5:18 pm

I've been in contact with the outfit in Malta ( Thanks Robt) and have now ordered 25 x VA1040 Thermistors. Used in this case for the Dynamic trip circuit, they are also found in radio and other audio circuits. I'm happy with 10 for stock so I will likely have 15 for sale at the price I paid plus postage, should anyone require one.

Back to the tripping PSU and over heating R609, as I mentioned above multiple possibilities, I started with the Chopper transistor R2010 (VT604) and that was found to be short.

Chopx.jpg
One dead chopper transistor

 
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Re: 1974 22" Ultra 6714: Thorn 3500 chassis

Post by crustytv » Mon Sep 05, 2016 9:31 pm

New R2010 installed, new mica washer and heat-sink compound. All PSU rails are now working. Despite now repaired whilst the module is opened up, I'm going to take the opportunity to replace a few of the tired caps and generally tidy up the few tacked in diodes. I will also run the scope over it to check the waveforms against spec. The I will hook up the line timebase module to the rig and PSU and again check the LTB waveforms.

newchop.jpg
Newly installed R2010, new mica and sink compound

psu-fixed.jpg
240V, 6.3V, 30V and 58-65V rails now all present.

 
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Re: 1974 22" Ultra 6714: Thorn 3500 chassis

Post by crustytv » Tue Sep 06, 2016 12:31 pm

This morning was a chance to take the newly acquired TEK DSO out for a test drive and check out the waveforms on the Ultra's PSU. Happy so see the 3500 switched mode PSU is performing faultlessly when various sections such as the Mark space, chopper etc were scoped.

Next Stage: The line time base module will be added to the PSU on the rig and tested. Once I'm happy these two modules are functioning then they will then go back into the set to see what we get on screen and how the I/F, Video, Decoder, frame and sound stages are fairing, hopefully something on screen from the CRT.

wv-1.jpg
-ve W615

wv-2.jpg
Mark Space

wv-3.jpg
Chopper Drive

wv-4.jpg
Chopper current

 
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Re: 1974 22" Ultra 6714: Thorn 3500 chassis

Post by Cathovisor » Tue Sep 06, 2016 12:51 pm

Nice waveforms, and a nice scope :)

 
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Re: 1974 22" Ultra 6714: Thorn 3500 chassis

Post by Briancuff » Tue Sep 06, 2016 1:30 pm

You've certainly learned a lot in the last few years Chris. You go about these restorations in a very professional way and are getting to know the foibles of colour TVs. Talk about the pupil exceeding the capabilities of the teachers - excellent thread and it's amazing to see such decrepit PCBs coming to life again.
How will you deal with the mouse damage?

 
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Re: 1974 22" Ultra 6714: Thorn 3500 chassis

Post by crustytv » Tue Sep 06, 2016 4:43 pm

This afternoon the Line Time base module was removed from the chassis and given a base line evaluation. This module is in quite remarkable condition, I suppose I'm basing that on the last hideous one I saw from the HMV 2703, this one by comparison looks new. There appears to have been little prior work carried out bar a few caps and those look to be fairly old changes themselves.

LTB-1.jpg

LTB-2.jpg

LTB-3.jpg

Time to hook this up to the PSU/Test rig. First thing to do is remove the fly-lead that has been attached to -ve end of W608. This is used to simulate the line pulse so you can check the 58-65V rail without having a LTB panel connected. Now we are connecting a LTB it must be removed.

With the Line Timebase connected and powered via PLG on the PSU, it was time to power on. All the rails came up and with an insulated screwdriver I was able to confirm the EHT pulse output was present on the EHT transformer nipple. Finally I scoped the chopper pulse and oscillator output, all looking very good.

LTB-a.jpg
PSU and LTB powered via the test rig. All rails present. chopper pulse displayed on scope and EHT pulse confirmed at EHT TX

pulse.jpg
Chopper pulse collector VT502

osc.jpg
Oscillator Output Base VT503

Next Stage: With the PSU and Line Timebase panels working time to reinstall these into the Ultra chassis, power up and see what we get, more to follow.

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