Hi there! I was pointed here from social media. I recently acquired an old Salora CRT TV from a thrift shop, untested, for about £5. It even had the manual, service schematics and original receipt of purchase (August 1980).
Being a rookie I fired it up after a quick dusting and it worked fine for a few minutes and then it started spewing smoke. To make a long story short the RIFAs are out and the canned cap and fuses has been replaced. After some other minor maintenance the set works great but it's not showing any red at all and this is where my problem lies right now.
Unfortunately my account is brand new so I can't attach pictures, but I've uploaded them here (I might be able to attach them to the post after the fact)
Mod Note: Photos added for you, five posts, and you will be able to upload
As you can see it even marks oscilloscope points and patterns on the silkscreen. It's like this set is made for fixing and learning <3
All sub boards are clearly defined both in the schematics and are easily detached from the mainboard.
Part of the problem is that I'm learning as I go here, my knowledge and experience is very limited. I don't even own a scope. I do have basic soldering and analytical skills however.
So, yes, the problem at hand is that the tube isn't showing any red at all. However since the rgb output board is so obvious I just tried switching the red and green outputs and the tube started showing bright reds instead of greens so I think we can rule the tube out and I know my input is good.
Using the front knob for saturation however does seem to produce proper grayscale (white bar pretty much looks white but I can't swear on it).
So with my limited knowledge I'm assuming that the problem exists in "PAL COLOUR DECODER" or "RGB OUTPUT" boards (located at the top portion, right of center, in the schematics). As far as I can tell it's the MC1327 IC that first produces R, G and B components so that makes me think the issue is either the IC or later.
BUT then again the saturation knob is connected to the TBA396 and when turned down the grayscale looks correct, which might point to something else.
Unfortunately this is where my lack of knowledge and tools keeps me down. Honestly this might be the project that makes me finally get a proper scope. But I also realize a scope alone won't fix this problem and narrowing this down can possibly be done without. I've checked for obvious breaks in solder joints and checked continuity a little randomly without anything obvious.
As a hillbilly solution I'm almost considering removing the MC1327 and attach it using leads so I can swap the output pins to see if that produces red on the tube so that I can possibly narrow it down to the RGB OUTPUT board or rule it out.
I don't understand enough about the signals to figure out if the problem can realistically be between TBA396 and MC1327 or IN them.
I'm hoping someone with a lot more experience than me can point me in the right direction =)
Cheers
Ground the Red Cathode, if you get a bright red raster, work back through the drive circuitry, if you don't, tube is shot. Don't leave it grounded too long as this will wear out the tube.
@mfd70 The OP says he has swapped the red and green leads to the CRT base and did give a red display so rules out a CRT issue, whilst I have no issues grounding the cathode with a simple class A output stage I wouldn't do it with this.
@CloakedAlien Does adjusting the red black level control RTY1 have any noticeable effect on the darker areas of the picture? If it does then the fault may possibly be a faulty ICF3 MC1327, if it doesn't then looks like an issue in the red output stage. I'm presuming you have a multimeter so take voltage readings on transistors TY1,2,3 and compare with TY4,5,6 noting any differences. It would be a good idea to check RY1, this is a special fusible resistor and can fail to protect the output stage from further damage due a fault but sometimes they fail for no reason at all. Welcome to Vrat by the way.
John.
@mfd70 Yes, thank you! I did try to switch the cables and I did get red so the tube is ok =)
@Jayceebee Awesome advice! Changing black level on the red did absolutely nothing, touching the same pot for green and blue made a huge difference with small adjustments. Does that mean we've narrowed it down to the output stage? If so that makes it a whole lot easier as the board is easy to detach and trace even for a rookie like me. I don't have IC probes for my multimeter and I'm a bit scared to short anything with the set live.
RY1 checks out at 1 koHm.
T1 = BC 237A
T2 = BF 258
T3 = BFR 88
I suspect the alternative is to desolder these and check with my ESR? How do I tell if they're not working as they should? And are they easily replaceable? (At least the T2 that are cylindrical are new to me)
Oh, I think I found it! RY5 is dead, infinite resistance. Now this just says 22K in the schematics but it's a bigger one, does that mean I have to get one rated for higher effect or would a standard one suffice 40 years later?
It does look as though the fault is in the output stage, before going too deep inspect the soldering of the transistors particularly T2 for dry joints. If you are confident you could even swap the transistors one by one from the red to the green channel and test, make sure the legs go in the correct holes with T1 & 3, it will be hard to get T2 in the wrong way round.
Not sure what you have for an ESR tester, perhaps it’s something similar to mine in the picture. Just simply connect the leads to each leg and a good transistor will give readings something similar. It will also tell you if the transistor is an NPN or PNP type.
EDIT posts crossed. Looks like you’ve found it then. An o/c RY5 would certainly cause the problem. Go with same value and physical size.
John.
@jayceebee Here's a picture of the resistor and ESR tester. I think I will replace this before doing anything else. I'm fully aware I might have more faulty components. Is this a 0.5 watt resistor? I seem to have 0.25watt resistors in droves so I might just order myself a pack of 0.5 watt resistors if that's the way to go.
Can’t see the pictures probably because you don’t have enough posts yet. What is the colour code on the resistor?
John.
Oh I got so excited I didn't realize I couldn't link images. I guess the admins spoiled me in my post =)
At any rate. I was measuring the body of the resistor and THEN checked the schematics. Let's just say they both agree it should be 0.5 watt resistors so I went ahead and ordered myself a pack. Hopefully I'll be able to test further tomorrow already.
Thank you so much for your input, this last clue gave me more confidence that the rgb output board was the culprit. Fingers crossed that's all there was. We'll know soon enough!
Hopefully that’s all that’s wrong, fingers crossed.
John.
Oh, the resistor is a 22k one as the schematics suggest (red, red, orange, gold)
The resistor pack I ordered claims 1% tolerance. I suppose that's fine as a replacement?
1% tolerance is much better than the original, gold = 5% as you probably know. As a test you could use a 10k and 12k 0.25W in series.
BTW your post count is 6 now so should now be able to upload pictures.
John.
Finally got my resistors, installed it, did a double-sanity-check and VOILA! This thing is ridiculous, look at those straight lines!
I realize this was an easy repair job, but it was a big job for me as a complete amateur. I've learned A LOT along the way and even got myself an oscilloscope (Rigol DS1102-Z), basically this is what pushed me over the edge, even though I didn't need it in the end. I'm also counting on errors arising over time but now I'm much better equipped to handle it.
The fact that this system is so easy to work in, that each sub-module is clearly isolated and removeable, has really made me learn a lot. It's fairly easy to connect the dots with the schematics, even the silkscreen is super obvious.
What I've also learned is that it's probably a fairly easy job to mod composite, or even rgb, inputs for this television. The mainboard has clearly marked which parts are live and which parts are isolated so it doesn't have live chassis as far as I can tell.
It's just a question of me understanding where to inject signals and how to do it safely, at least I understand whereabouts the signals are processed and handled so with a little guidance it should be doable. But I suppose that's a topic for another thread =)
Big thank you for the help in narrowing this down!
Well done for finding the fault, swapping the leads of the cathode drives helped as did adjusting the background pot and noting the effects. Having an accessible chassis is a big advantage also.
You are correct that the chassis is mains isolated so adding external inputs will be OK without the need of a mains isolation transformer. Looks quite simple to add a composite video input, a buffer stage will probably be needed but RGB will be more of a challenge.
Excellent work.
John.
Nice work and great to see someone else who's into retro gaming! As much as a lot of people in TV repair circles don't like to admit it retro gaming is the one thing which is going to keep CRT TVs going long into the future.
The weird thing is you might find that some TVs can produce a better picture via RF than some can using composite. My 1978 Pye CT450/G11 is one such TV.
Thank you!
Yes, I'm heavily into lots of retro stuff. Not just consoles but also computers of various type so there's no shortage of where more troubleshooting skills can come in handy =)
I'll hopefully start a new thread for possible inputs mods in the near future.
@cloakedalien oh yes, I do love my retro computers. There's a thread in this very forum on getting my Amiga 2000 up and running as well as putting the guts of a 00s 14" Asda-brand TV into the shell of a dead Commodore 1942 monitor.
