Early CTV IC Faults

Introduction

Inevitably as you start to collect and repair early colour TV’s and as you move away from hybrids, all those thermionic bottles start to disappear. Just when you thought you’d had enough of those few three-legged  (Transistors) beasties they multiply by the 10’s. Worse still IC’s start to make their presence felt and woe betide the careless probe.  As early as 1968 you will come across the multi-legged packages, the Baird M718 probably being the first using the RCA CA3034V1 (see below). It was used for all the signal processing components with the exception of the phase-detector transformer  and contained within a  10 pin TO-5 can.

First use of an i.c in a British Early Colour TV :

1968: The Baird M718 Signal processor.

1969 saw the the more familiar i.c. packaged SL901 appear in the RBM A823 decoder, during the early 70’s and onward the use of i.c’s was on the increase.

SL901B

Servicing Techniques

It must be made clear from the very start that there’s no room for errors. Don’t short-circuit any of the pins together, and be careful when making voltage and resistance readings. The first thing to check is whether the supply voltage is reaching the i.c. As for EHT flash-overs, well unlike the bottles of old, the sand packages just object. I found this out the hard way on a PYE CT203 with the decoder and field boards being decimated by a flash-over.

When removing an i.c. that’s soldered into the circuit, do so neatly and keep the i.c. as cool as possible. I use a Weller desoldering station which makes the job much quicker, a solder sucker or braid works but it’s worth spraying the i.c. with freezer to keep it cool. You may have to put it back in circuit, this can be done by hand or there are I.C. tools for DIL packs are available online, there’s plenty on e-bay. One good thing about an insertion tool is they automatically align the pins should they be bent. Some chassis’ use socket i.c.s, this makes replacement far easier. Take care not to bend or snap any of the pins, they are very fragile and easily break. If a set has been poorly stored then expect severe corrosion to put an end to the package as can be seen from an example below. This i.c. was found on a poorly stored Thorn 8500 chassis, no wonder the set was suffering from its effects.

Make sure the i.c. is inserted the right way round and if unsure consult data, its also worth taking photos. Always replace any heat-sinks and renew compound or the i.c. will be ruined. After replacement check that all the pins have been soldered and that there are no solder shorts from one pin to another or solder blobs shorting adjacent print tracks. It’s worth checking with the manual in case there are any instructions or warnings regarding the use of the multimeter or scope. I.C. test clips for DIL packs are available and make testing easier.

Taking a voltage map will be the greatest help in deciding whether an i.c. is faulty, though readings at the output pins will depend on the inputs. Certainly looking at waveforms with a scope will make life a lot easier too and again not forgetting the other useful aid, freezer spray.

The following stock faults covers most of the common early i.c.s you are likely to encounter on early colour television repairs. As I state at the foot of the page if you know of others please leave comment.

Tuning Voltage Stabilisers

The three i.c.s commonly used to stabilise the supply to the varicap tuner’s preset tuning controls are the TAA550, ZTK33 and SN76550. All can fail to do this, producing tuning drift. Symptoms are intermittent loss of signals or weak signals or loss of colour. On the Philips G8 chassis the fault usually develops when the receiver is hot, so that the application of freezer will temporarily cure the trouble. Note that there are 30-32V, 32-34V and 34-36V versions. The TAA550 and SN76550 are colour coded (red, yellow and green respectively) while the ZTK33 carries the suffixes A, B or C.

IF Strip ICs

MC1330: Widely used synchronous video demodulator i.c. Can be responsible for no sound or vision (blank raster) possibly with spurious sound; poor sound and vision; pulling on captions; video smearing.

MCI349: Vision i.f. gain i.c. .used in the Decca 80 and 101 series chassis. Can be responsible for severe ringing.

M5183P/SC9431P: Vision i.f gain i.c. used in the Mitsubishi Models CT180B, CT202B and CT203B. Can be responsible for no raster, no sound, or a noisy picture.

SC9503P: Synchronous vision demodulator i.c. used in the Rank Z179 chassis. Can be responsible for a blank raster or intermittent loss of vision.

SC9504P: Vision i.f. gain i.c. used in the Rank Z179 chassis. Can be responsible for low gain or a very grainy picture.

TBA440: Vision i.f. gain/detector i.c. used in some German sets. Can be responsible for no sync, no colour or a blank raster.

TCA270: Widely used vision synchronous demodulator i.c. Can be responsible for loss of or weak sync (check output at pin 10), a blank raster, or a weak picture.

Jungle ICs

The “jungle” i.c. is a video signal/a.g.c./sync processor.

TAA700: Can be responsible for loss of vision or no line sync.

TBA550: Can be responsible for loss of vision. Intercarrier Sound ICs

M5143P: Used in the Mitsubishi models previously mentioned. Can cause no or distorted sound.

MC1358PQ: Can cause intermittent, distorted or no sound Also caption buzz and noise.

Intercarrier Sound IC’s

TAA350:Early device providing gain only. Can be responsible for no sound. Commonly caused caption buzz on earlier versions of the Rank A823 chassis, on which it can also be responsible for distorted sound.

TAA570: Can be responsible for no sound, possibly intermittent, or very low sound.

TBA120S: Can cause no, low or distorted sound, and caption buzz.

TBA480: Can cause no or intermittent sound.

TBA750: Can cause loss of sound, possibly intermittent,low sound, and caption buzz.

Audio

TBA800: has been quite widely used and can be responsible for no, low or distorted sound. Korting hybrid sets use either discrete audio circuitry, a TBA800 or a TAA640. Both these i.c.s can be responsible for loss of sound on these sets.
Note: however that the fault can be the result of a flashover in the tube. If you fit a new, say regunned tube, it’s a good idea to remove the sound board. If the new tube produces continuous flash-overs, fit another.

Timebase ICs

TBA720: Used as the line oscillator in Philips and Pye solid-state monochrome chassis. Can be responsible for no sound or raster due to no line drive. With this i.c. it’s most important not to attempt voltage or waveform checks in the oscillator section. Check only the supply line, never at pins 12 or 13 or adjacent to these pins. Note also that there are two versions, the TBA720Q and TBA720AQ: these cannot be interchanged without making circuit alterations.

TBA800: Audio i.c. used as the field output stage in some monochrome portables. Can be responsible for field collapse.

TBA920: Widely used sync separator/line oscillator i.c. Can be responsible for no sound or raster due to no line drive; loss of line sync; no field sync.

TBA950: Sync separator/line oscillator i.c. Can be responsible for no sound or raster due to no line drive; loss of sync (maybe intermittent); incorrect line speed.

Tuning ICs

ETTR6016Q: CMOS i.c. used in GEC touch-tuning system. Can stick on one channel or jump from one to another erratically.

SAS560S/SAS570S: Combination for use with touch tuning systems. Can be responsible for erratic channel changes or sticking on one channel. On ITT hybrid sets can be responsible for no raster or sound with the selector stuck in one position, since the 20V rail is removed when one or both go short-circuit.

TBA625A: Provides a stabilised 5V rail for the Telecommander remote control system used in some Saba sets. Can cause erratic or random channel selection when it fails to stabilise the supply.

Decoder ICs

MC1327P: Widely used chroma demodulator/RGB matrixing/PAL switch device. Can be responsible for loss of luminance, loss of one colour, no colour (possibly intermittent), Hanover bars at the right or the left of the screen,or white streaking. On the Decca 30 chassis you can get a reddish or magenta cast on switching on, persisting for a short period before correct colours appear. This can also be due to RGB output stage defects however.

SL901: Chroma demodulator/RGB matrixing i.c. used in the Rank A823 series chassis and Z179 chassis. Early types are fitted in a 20-pin pack, later ones suffixed B have a 24-pin pack. Often causes a negative picture. Other faults for which it can be responsible are loss of luminance, loss of one colour (maybe intermittent), and loss of the B – Y or R – Y signal. Note that one of the causes of a faulty SL901 in the A823 chassis is a flashover on the power supply due to a dry-jointed thermistor or a burn right through the panel. This causes a chain reaction, ruining the SL901 and the associated SL917. The decoder backs on to the power supply panel, and the tell-tale signs are a black burn mark on the right side of the decoder, on the print side.

SL917A: Chroma/burst signal processor used in the Rank A823A and A823B chassis. Can be responsible for no colour, intermittent colour, a purple and green picture or a smeary picture (rare). See note above.

SL918: Chroma/burst signal processor used in the Rank Z179 chassis. Can be responsible for loss of colour or intermittent colour.

SN76226: Chroma and luminance signal processing and black-level clamp i.c. used in the Thorn 9000 chassis. Also contains the sync separator. Can be responsible for no raster with the sound normal and e.h.t. present. To check, switch the set off and remove the i.c. If the raster returns on switching on again the i.c. is faulty.

TAA630: Chroma demodulator/PAL switch i.c. used in the Korting hybrid colour chassis and early versions of the Philips G8 chassis. Can be responsible for no colour.

TBA500: Luminance amplifier, with black-level clamp and beam limiter control

TBA510: Chrominance signal processing i.c. Can cause intermittent loss of colour (Grundig sets).

TBA520: and TBA990: These are colour demodulators of successive generations. They incorporate the PAL switch and synchronously demodulate the U and V chrominance signals, at the same time matrixing G-Y from the resultant R-Y and B-Y outputs.

TBA530: Widely used RGB matrixing i.c. The usual fault is a bright red, green or blue raster, possibly intermittent. An RGB output stage fault can also cause these symptoms of course.

TBA540: Widely used reference oscillator i.c. Can be responsible for loss of colour (maybe intermittent), odd colours, and Hanover bars.

TBA560A: Luminance/chrominance signal processing i.c. Can be responsible for flyback lines in Telefunken models.

TBA560C: Widely used luminance/chrominance signal processing i.c. Can be responsible for a blank raster, uncontrollable brightness, or no colour.

TBA970: Luminance signal processing i.c. used in many Grundig receivers. Can cause loss of luminance (maybe intermittent), and no beam limiting action.

TBA990: Chroma demodulator/PAL switch i.c. Can be responsible for loss of one colour or an all red, green or blue raster.

TCA800: Widely used chroma demodulator/PAL switch/matrixing i.c. Can be responsible for loss of colour,loss of one colour, or loss of R – Y or B – Y. Note that a faulty i.c. causing excessive brightness in the Saba H chassis will result in the set switching itself off shortly after being switched on, due to the excess current trip coming into operation.


That’s it for now of course there are many others, as and when I find info I will update. However if any of you ex TV engineers out there in vintage telly land with your encyclopedic memory have anything further to add, then please feel free to add more useful tips using the comment form below. Remember you don’t have to be a member guests can leave comments also.

 

Leave a Reply

dialog-information.png
Important Notice: To leave a comment use the box below. You must tick "I'm not a robot" and then complete the puzzle, otherwise the automated comment system will reject your post and treat it as spam.
 

Your email address will not be published. Required fields are marked *

*