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1977 Ferguson 3734 ColourStar: Thorn 9600 Chassis

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crustytv
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Caution: This thread comes with a "likely to bore" rating
I'm acutely aware my over the shoulder, as it happens type threads, have in the past bored some folk rigid.  I tend to ramble on for many pages and for that I apologise in advance. I adopted this approach as I felt it was/is a great way to comprehensively document a sets repair, encourage member participation especially for those among us who don't have a collection of their own but like to partake in some way. Finally a comprehensively covered repair with wart-N-all,  in many ways may be of benefit to others in the future. If at any point in time you feel enough is enough, feel free to tell me publicly or privately, to stop.  I will take a break so others can have their threads gain some "air time".


Let the Story commence

After having a break from the 1967 and the Ferguson 3700 2K resurrection I was wondering what on earth to do next. As is customary with my threads, I set the controls on the CTM "Crusty-Time- Machine", this time just mashed the pad and it so happened to land me 10 years later. 

Now arriving in 1977 I'd forgotten what a pretty bleak time for the UK it was. Endless strikes but we'll avoid the politics. Its the Jubilee year too, 25 years on the throne for queeny. Fleetwwod Macs Rumours was released, Mike Leigh's Abigail's Party, a hit. A superb year at the movies  with the release of Star Wars, Saturday Night Fever & Close Encounters to name but a few. But wait! weird folk wandering about, pins through their noses, trouser legs chained together and huge spikey hair-do's,  Spiting and head butting each other whilst doing a move called the po-go........  ?

Escaping from the mayhem I cut down an alleyway and came across a TV shop, in the window was this years new offering. A  very nice 22" Ferguson 3734 Colourstar sporting the latest chassis from Thorn, namely the 9600. Oooo even has a new fangled feature , touch-tuning. That'll do I thought, nabbed it and hot footed it back to the Crusty Time Machine to land safely back in the workshop in 2018.

This set just slips in to my area of interest namely 1967 - 1977.

3734 2

 

chassis

Those that have followed my threads before over on Vrat 1.0  will know I've tackled many Thorn 3000 SMPSU, they used to intimidate me when I first started working on them, however time and tackling many, has left me with a high regard for them and an equal fondness to work on them. Syclops still scares me, so its probably a good idea now we're here on Vrat 2.0 that I recap how syclops functions.

SYCLOPS

The syclops control circuit has to ensure that both the line output transistor and the chopper transistor are driven synchronously by the same drive waveform, hence the term Syclops. SYnchronous Converter and Line Output Stage.

The syclops control panel therefore has to provide a drive waveform which is suitable for both these stages. The requirements of the line output stage are that the drive must be removed at the end of the scan to initiate fly-back and that the drive must be restored before the efficiency diode stops conducting at time t2. (see below)

The only requirement of the SMPSU is that the on/off time of the drive can be varied in order to keep supplies constant despite variations in the mains input and/or changing load demands made on the supplies. Since the drive must be on between t2 and t3 for the line output stage, the only way that on/off time can be altered is to vary the point at which the on time occurs between t1 and t2.

wavefm

 

The maximum on time is set by the syclops control circuit to limit the dissipation of the switch mode transistor to a safe level. It is possible to turn the drive on during this period without affecting the operation of the line output stage because the line output transistor is reverse biased by the negative potential at its collector due to conduction of the efficiency diode which produces the first half of the scan.

Another Cool Feature

The 9600 offers diagnostic sockets TSA (Scanning) and TSB (Power Supply). The 9600 can be operated with any suspect daughter board removed without causing damage to the set. Therefore making use of the diagnostic sockets TSA & TSB you can determine if the expected voltages are present along with removing the supply rail fuses, isolate the fault/trip condition.

3734 3

The 9600 is a service engineers dream with amazing access to all the panels, which I will demonstrate in the next post. I have the suite of Thorn manufacturers service manuals to hand and I have to say they are the most comprehensive I've come across, I suppose with a complex chassis such as the 9600 its certainly a must have.

3734 1

The Set 

The CRT is PIL A56 611X

Well that's it for the opening of the thread except to say the sets fault condition is constant tripping. The next instalment will be me making use of the diagnostic ports to see if the source of the tripping can be narrowed down. Oh and I nearly forgot, on the side is a service sticker stating "frame collapse". I've no idea if that is an old fault that was cleared, or why the set was laid up all those years ago.

Up Next......?

The chassis inspection, how it extends for ease of access and serviceability 

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Topic starter Posted : 16/05/2018 4:27 pm
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PYE625
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Posted by: Chris

Caution: This thread comes with a "likely to bore" rating
I'm acutely aware my over the shoulder, as it happens type threads, have in the past bored some folk rigid. 

If I for one found it boring, and any other thread or post by anyone else for that matter, I would have to question my interest in the hobby. So please continue ! ? 

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Posted : 16/05/2018 5:49 pm
Cathovisor
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Great, a chance to sit and watch some telly (being fixed)  ? 

One of my aunts had one of these, but (IIRC) badged as an Ultra.

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Posted : 16/05/2018 5:50 pm
Marc
 Marc
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It's been a long while coming Chris and I for one am looking forward to the saga continuing.  

Great stuff ! ? 

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Posted : 16/05/2018 6:32 pm
crustytv
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Lets get intimate with a brief look under the bonnet

As I explained in the initial post the 9600 like all its predecessors, have the service engineer in mind. The 9600 chassis as a whole is withdrawn on two lower plastic rails, the chassis is released from its lock position by pushing in two tabs, lower left and right, finally unhooking the top plastic lock bar.

chas 1
chas 2
chas 3

Now with the whole chassis extended back by about 8 inches it gives access to all the modules. The lower scanning module with E/W correction, left Switch Mode PSU – Line and Frame Oscillator Module – SYCLOPS Control Boards, the I.F -Video & Chroma board and the tuner/ audio module scan be extended and swung outwards.

Now we can now take a look at each one in turn

The Switched Mode Power Supply: With Syclops control, Line & Field Oscillator

sect 1
chas 5
chas 10
chas 11

The Scanning module & E/W correction module

sect 2
chas 4

I.F -Video & Chroma module

sect 3
chas 12
chas 14

Touch Tuner – Audio Output

sect 4
chas 7
chas 8

The Thorn A56 611X PIL Tube

chas 9

As you can see quite a lot packed into this one. Its pretty neat that on the panels Thorn have supplied flow diagrams with voltages and expected waveforms, excellent for servicing reference. The daughter modules on the SMPSU can be removed and plugged in on the reverse side further aiding service access.

I suppose before I progress any further the next step should be to determine the state of the CRT. This will dictate if I should continue it might be a dud, it might be low but can be recovered or it luck is on my side, it might be a goodun.

Next.......instalment? CRT testing.

 

 

 

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Topic starter Posted : 16/05/2018 8:53 pm
sideband
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Interesting set. Now the SYCLOPS......was that similar to the Salora IPSALO (Integrated Power Supply And Line Output)? I think Grundig did something similar as well. I fixed a few of those as private jobs by just replacing some diodes and a few electrolytics. 

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Posted : 16/05/2018 9:09 pm
Jayceebee
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I too have been waiting patiently for this one to land on your workbench, let's see what memories come back from the depths of the old grey matter (if anything these days  ? ).

A couple of things that do spring to mind is the Rifa capacitor in the mains filter block which I'm sure you will know about, those blue Welwyn high wattage resistor where the metal loops on the mounting legs which fit over the end caps break and part company with the resistor body, also a 1200pF disc ceramic capacitor in the snubber network which can produce fireworks before blowing the fuse. I don't remember it's ref number but the original was an ice blue colour somewhere near the heastink on the power pcb, the replacement was 1500pF 2kV.

John.

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Posted : 16/05/2018 9:26 pm
crustytv
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Hi everyone,

thanks for all your comments & posts thus far, its encouraging to know you're all up for another crustytv saga.

As I had been working in the era of the late 60's I wanted to come forward to mid to late 70's. Therefore it was between this set the wired Rediffusion CH2213 with its Frequency translator box. I must admit @jayceebee it was a little voice on my shoulder, your voice to be precise, taunting me "go on, face Syclops once again".   

Its certainly been a while, probably about three years since I last played with a 9000 series chassis. Thick and thin film units are a worry, I have some in stock but we shall have to see how it plays out. Thanks for the service tips, I'm sure they will come in handy  ? 

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Topic starter Posted : 16/05/2018 9:41 pm
Jayceebee
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Posted by: Chris

Thick and thin film units are a worry. 

Absolutely nothing to worry about in that respect apart from the focus control as none have active components, if I remember rightly they are just multiple resistor packs and 99.99999999% reliable.

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Posted : 16/05/2018 9:54 pm
crustytv
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Update 

Excellent news, the A56 611X is a good one so the repair can go ahead. 

crt 1
crt 2
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Topic starter Posted : 16/05/2018 9:55 pm
PYE625 liked
crustytv
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Posted by: Jayceebee
Posted by: Chris

Thick and thin film units are a worry. 

Absolutely nothing to worry about in that respect apart from the focus control as none have active components, if I remember rightly they are just multiple resistor packs and 99.99999999% reliable.

That's a relief John, I saw a few dotted about and without consulting the data got a little concerned. Good to know they're trouble free. I seem to recall I had an OVP film unit and a resistor pack that had failed on a previous 9K can't remember which one now.

 

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Topic starter Posted : 16/05/2018 9:59 pm
Katie Bush
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Flippin 'eck Chris,

You couldn't get a much better CRT that that! I'm assuming it's had no 'ju-ju' magic done on it? - It's certainly well balanced on emission......

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Posted : 16/05/2018 10:27 pm
Marcus 3700
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Hi Chris,

It certainly looks very full in there! Looking forward to your exploits with this set!

Marcus.

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Posted : 17/05/2018 12:47 am
crustytv
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And So It Begins..........

Power applied to the set, I hear sort of static rustle but dead! Removing the screening plate from the PSU gives me access to the PCB side and the TSB diagnostic pins.

dead 2

First is to check what voltage I have on pin 9, I find there is 580V. Next to check F511 which supplies 34V to the 24V regulator, which in turn supplies the field Osc an output stages, width and height compensation circuit, E-W raster correction and the IF decoder modules. 

dead 4

Here I find F511 was open,  I tried another just in case but it blew straight away.

dead 3

Next is why was it blown in the first place? A potential short on the 34V rail ? Hmmm sort of ties in with the field collapse sticker I found on the cabinet side. I'm tempted to isolate the scanning panel and see if the fuse stops blowing.

According to the manual if F511 is blown check for a short circuit on the 34V line.  A resistance check of PL518/1  to chassis should be: +ve lead to pin PL518/1 and -ve to chassis - charges to 450R. Now -ve lead to PL518/1 and +ve to chassis - charges to 850R. My tests give 2.8M and OL respectively. 

psucct

 

 

 

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Topic starter Posted : 17/05/2018 11:29 am
Nuvistor
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Is that the 24 volt regulator at the back left of the line scan board, the tab on the transistor looks rusty?

 

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Posted : 17/05/2018 12:18 pm
Cathovisor
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Posted by: Chris

 

According to the manual if F511 is blown check for a short circuit on the 34V line.  A resistance check of PL518/1  to chassis should be: +ve lead to pin PL518/1 and -ve to chassis - charges to 450R. Now -ve lead to PL518/1 and +ve to chassis - charges to 850R. My tests give 2.8M and OL respectively. 

But don't forget those measurements in the manual were made in all likelihood with an AVO 8. Your posh new meter may well give a very different result.

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Posted : 17/05/2018 2:17 pm
crustytv
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As ever with my projects they take a step backwards before moving forwards.

The set is now its blowing F1 so that fault needs clearing first to enable me to get back to diagnosing F511 blowing. W525 and associated components are suspects.

 

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Topic starter Posted : 17/05/2018 2:23 pm
Cathovisor
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No, that's good - it's all educational and let's be honest, you'd be dead bored if it just worked now wouldn't you?! 😉

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Posted : 17/05/2018 2:26 pm
crustytv
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I removed W525 from circuit, tested and its failed, so that's the cause of F1 blowing. Typical it decided to fail whilst I was trying to track the cause of F511 blowing. I do have a large stock of diodes but I'm not sure what I've got in the way of BR's.

brdead
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Topic starter Posted : 17/05/2018 3:52 pm
Cathovisor
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Shouldn't be too hard to source a new one of those, Chris. 2.5A 800V IIRC - RS used to sell exactly the right part once!

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Posted : 17/05/2018 4:02 pm
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