Hi all, wonder if anyone can help. I'm relatively new to collecting Televisions, and have bought myself a Thorn Ultra Model - 6845 set but when plugged in it does not usually work, and very occasionally it will power up for a split second and then the screen will go blank but it still hums
Any advice would be appreciated.
Kind regards,
Will.
Hi Will, and welcome to VRAT.
Before the guys pitch in and try to assist you, it would be very helpful for us to know your level of experience, and what equipment you have to aid fault-finding. You state “I'm relatively new to collecting Televisions”, would this mean you might have experience on vintage radios or perhaps not those either?
It's important for us to know, so advice can be pitched accordingly, therefore a few questions. By the way, there's no magic answer that will miraculously get your TV going.
- Have you any experience of vintage electronics or electronics in general? For example, do you understand resistors, caps, diodes, transistors etc, their function, and how to test them?
- Can you read and understand circuit diagrams? This for example.
- Do you have a multimeter & know how to use it for taking resistance and voltage readings? Much can be ascertained using cold checks (TV powered off) rather than hot, (TV powered on) and it's much safer for you doing 'cold-checks', if you're a novice.
- Do you have a soldering iron?
Best to start fault-finding at the power-supply and the associated rails, before diving in too deep.
By the way, your Ultra uses a Thorn 1690 TV chassis and dates from 1977/1978. I have the service data for the set and will scan that in due course.
You will be pleased to know we have a couple of Ex Thorn Television engineers in our ranks, and of course many other Ex TV engineers. As well as seasoned amateurs, so I'm sure they will be along and keen to offer their opinions.
As Chris states, first check the PSU, it’s a simple series regulator, also check plugs and sockets if there are any on the PCB for bad connections.
I'd bet it is the 12V DC input socket, the hum is probably just from the mains transformer, bit of switch cleaner and insert and remove a suitable DC plug in and out a few times, or else if you are confident just bypass it if you never want to use it on 12V DC.
@crustytv Hi, apologies for the very late reply, had a few things to sort out this end, I've never worked on anything like this before, my Dad is going to help me tomorrow to try to identify the problem with his multi metre.
Thank you for getting back to me all the same
Kind regards,
Will.
Hi all, had a look at the set with my Dad, he thinks it might be the 2amp fuse in the back as it is looking a bit scorched, any idea where I can find some 2amp resistor fuses?
Thanks in advance,
Will.
To be certain, test the fuse with a mutilmeter to be sure, otherwise it's just a guessing game.
If it is actually open, then it went open for a reason, a fault. You could just stick in another, but chances are it will just blow again, due to the underlying fault, then you're back to square one. No escaping it, proper fault-finding is required, and then we're back where we started, the points I raised in post No.2 above.
Fuses are available from many online outlets, eBay as well.
....and don't assume it is any old 2 amp fuse! There are many types but the main two used in TV's are quick blow and slow blow (Time Lag)...the names should be sufficient to understand the basic difference. Look at the fuse markings. It could be marked F2A or T2A. F2A will be Fast blow, T2A will be Slow blow (Time-lag). It is IMPORTANT what type is fitted depending on what the fuse is protecting. If you fit a fast blow in place of a slow blow, chances are it will blow straight away EVEN IF THERE IS NO FAULT!
If you are not sure, try to identify what part of the circuit it is protecting (you'll need the circuit diagram) and come back here.
....and don't assume it is any old 2 amp fuse! There are many types but the main two used in TV's are quick blow and slow blow (Time Lag)...the names should be sufficient to understand the basic difference. Look at the fuse markings. It could be marked F2A or T2A. F2A will be Fast blow, T2A will be Slow blow (Time-lag). It is IMPORTANT what type is fitted depending on what the fuse is protecting. If you fit a fast blow in place of a slow blow, chances are it will blow straight away EVEN IF THERE IS NO FAULT!
If you are not sure, try to identify what part of the circuit it is protecting (you'll need the circuit diagram) and come back here.
Tried an equivalent 2 amp fuse and hasn't made a difference so it appears to be something else.
Check you have voltage both sides of the fuse holder. if the holder as been getting hot due to high resistance contacts the contacts will have a grey appearance to them and will have lost the springiness and thereby the grip on the fuse. You said the fuse looked a little scorched... Intermittent fuse holders were not uncommon of some portables, the 1590/91 could suffer from this causing intermittent operation.
