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Serviceman's Log

The Televideo that committed hari-kari

By The Serviceman

Items Covered This Month
  • Akai VS-G425EA VCR.
  • Teac MV1440 Televideo.
  • Philips 14GR1224/75R TV set.
  • Sony DVP-S735 DVD player.

Some years ago, I gave my mum a Teac Televideo (MV1440) for her birthday. It was perfect for her little bedroom and she could lie in there and watch her recorded soapies to her heart’s content.

Recently, to everyone’s surprise and relief, my son actually got a job as a warehouse assistant. This was fine until one day the ancient warehouse roller door decided to jam in the open position.

Unfortunately, the earliest anyone could replace the door was the following week, which meant the warehouse had to be left open to the world. The consternation about security concerns this caused management was enormous until my son, who had just learnt about overtime, put his hand up to become nightwatchman. This appealed no end to the management who eagerly agreed to this arrangement.

My son quickly went home to get some essentials, like a six pack (of light ale) and his Walkman. He also persuaded his granny to lend him her prize Televideo – to get through the wee small hours.

He arrived back at the warehouse, unloaded his van and proceeded to build a little nest in one corner of the warehouse which was in a good position to view the broken garage entrance. The TEAC was placed precisely on top of an old oil drum but unfortunately the reception was lousy with the indoor aerial. Apparently, he was fiddling with the aerial in an attempt to improve the reception when the accident happened.

The way he tells it, it was the set that had deliberately committed hari-kari. The way I saw it, he had pulled the lead too hard and the set fell off the oil drum and landed very heavily on its back on the concrete. He brought it to me the next day, sheepishly pleading: "Please fix Gran’s telly . . . and please don’t tell her anything".

Well, I took it to the workshop but as soon as I had removed the back, I could see that the set was a write-off. The neck of the tube had broken and the motherboard was cracked. What could I do? I went around to a rival TV repair shop whose main line of business was buying, restoring and selling secondhand TVs.

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I’m on good terms with them and so I asked if by any chance they had a Teac MV1440 in stock. We went down into their warehouse and had a rummage. The only thing they had was an MV1480 MK II, which is a later model, but it did have some faults. Apart from being filthy and having the front flap missing, the set worked a bit. There was no sound and a washed-out snowy picture on-air. The video was also working but there was just a snowstorm on playback. However, this all worked to my advantage in the price negotiations.

Back at the workshop, I started with the video playback, which turned out to be very dirty heads. A careful wipe of the heads axially with a lint-free material and oil-free acetone cleaned them thoroughly. The sound fault was more difficult to find but in the end turned out to be an intermittently open-circuit loudspeaker. All I was left with was the snowy off-air pictures.

First, I checked the aerial socket and for continuity to the extremely small Murata tuner. I then checked that the set was able to tune in all the stations on VHF and UHF, which it did – albeit slightly snowy. I then checked the RF AGC (it was about 6.5V) and found that the AGC control in the separate equally small IF module also worked but adjusting this didn’t clear the fault.

Although I had the service manual for this model, the circuit is not drawn for the tuner or IF modules which are just shown as block diagrams. I was faced with a dilemma – was the tuner faulty or was it the IF module or both? I was satisfied that all the voltages into both were correct. The big downer in this progress was that the tuner alone had a trade price exceeding $108 and the IF unit over $172.

To narrow things down, I connected another tuner in place of the original and found that the picture was more or less the same after retuning, which to my mind eliminated the tuner. I then removed the IF module and examined it. It consisted of an IC, several coils and ceramic filters, and several surface-mounted components, including three transistors. I checked the transistors and this revealed that the SAW filter driver (or first IF transistor) was open circuit.

Unfortunately, I didn’t know its type number, so I had to try a different approach. I looked through a pile of scrapped TVs and videos, searching for a similar surface-mounted transistor which was performing the same function. I eventually found one in the IF stage of a Hitachi video and swapped them over. And that did it – after retuning and readjusting the AGC control, I could finally tune in perfect pictures.

A bit of "Nifti" cleaner and some polish cleaned the rest of the set up nicely. Finally, I checked that the old remote control worked the newer model which it did.

Granny was surprised to get back a different set but found that the new one gave a better picture. As for my son, he’s traded the repair for a few months of lawn mowing and other domestic duties.

A crook Akai VCR

Mr Jones brought in his Akai VS-G425EA video, complaining that it was chewing up his tapes. Unfortunately, he didn’t bring in any of his tapes; nor was he clear what he was doing when the tapes got damaged.

Fortunately, I have a large box of ruined tapes for such occasions. I removed the covers, put a tape in and it immediately laced up against the drum and played OK. It could also fast forward and rewind but was intermittently slow in bringing the tape back into the housing. It would also sometimes leave tape loose on top of the deck so that when you pressed eject, the cassette door would close, leaving the tape outside to get all "scrunched" up.

My immediate assumption was that the idler reel was faulty and sticking and not providing sufficient torque to pull the tape in whenever the mechanism unlaced the video heads. I removed the whole deck which is very easy these days – undo five screws and pull three assorted plugs and sockets and it’s out (after you have removed the front escutcheon, of course). I removed the reel roller, examined it closely but could find nothing wrong to the eye. I put a new one in just in case and replaced the belt as well.

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Unfortunately, they made no difference. The reels were running free, with no hindrance, so the problem had to be elsewhere.

My eye now moved onto the next suspect, the mode select switch. This VCR isn’t very old and looks new with little wear. Mr Jones is an old age pensioner but doesn’t watch many video movies, so why would you expect trouble with a fully encapsulated rotary switch underneath the deck?

Yeah, well I wish someone would tell me because replacing it fixed the problem completely. In fact, before I did that, I lightly squirted it with CRC 2-26 and that also fixed it. I then opened up the switch to have a good look inside. It looked immaculate, nice and clean with a transparent layer of light switching grease to protect the metal surfaces.

Despite all this, apparently the contacts had gone high resistance, hence its early demise. Cleaning and re-lubricating them will work for a while, but clients demand much more these days!

GRI-AX revisited

Over the years, I have seen many Philips GRI-AX chassis TVs. By and large, they have been an excellent series of models which have performed well and have been mostly easy to fix – that is, until recently!

Mr Sorensen’s 11-year old 14GR1224/75R was dead and he sensibly brought it in because it is a lightweight and it’s always easier to bring the set to the workshop rather than vice versa.

The set was slightly corroded inside but consistent with its age, and it didn’t take long to work out that the flyback transformer and line output transistor were both cactus. Both were replaced and the set left on soak test for several days before Mr Sorensen came to pick it up.

As is my policy on all TV repairs, if there are any dry joints in the set (and which set doesn’t have any?), I set to work and resolder them. The GRI-AX is very prone to dry joints, especially around I7020 and the line output stages, but after a thorough soak test, I was very confident that all would be well.

But it was not to be. Three weeks later he brought it back in, saying it was dead again. I lent him another set and had another go at it. Intermittent problems with this model are invariably due to the SCR crowbar current switching on prematurely. By measuring the voltage across C2660, or more conveniently from the anode of the SCR6641 to ground, which should be 97V, you can then adjust VR3625 until the SCR fires – theoretically at about 101V or so.

If it is less than this, I change zener diode ZD6640 from 30V to 33V, or even higher if necessary, and then repeat the adjustment. When satisfied it is firing at the correct point, I then reset the voltage for 97V or less.

The other thing that should be done is to replace C2523 with a new 10μF capacitor and also replace C2542 and L5524. With all that done, I was feeling bullet-proof but this set only worked for another day before it died again and stayed dead.

I was so glad it had happened in
the workshop and not back at Mr Sorensen’s house. And I was even happier that it was now permanently dead because this gave me a better chance to nail the problem properly.

I soon found that the remote control could switch the set on from standby, after which the red LED would go out. There would then be a "wimpish" noise from the set as it tried to come on, before ultimately failing.

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It was time for some voltage measurements. The full 97V was available right to the collector of the line output transistor (TR7528) but the 9V startup voltage was way down at about 6V. Using an oscilloscope, you could see the correct waveform start to build up all the way from pin 26 of IC7020, through TR7521, TR7523 and TR7528 – but it would always collapse almost immediately.

The set is designed to start with 9V and then have the 12V take over from the flyback transformer via D6542. I had already replaced the flyback transformer (T5530) and the line output transistor (TR7528), so now I fitted a new IC7020 into a freshly soldered 28-pin IC socket. This made absolutely no difference so I then swapped the chassis with one from another nearly identical set that was also in for repair but the main chassis still refused to fire up properly. Grasping at straws, I next desolder­ed the sound output IC (IC7103), as this is often troublesome and can provide an unacceptable load when the set is attempting to start. This still made no difference.

Finally, I connected an external power supply to the cathode of D6635 and wound it up to 10V before switching the set on. Bingo! – it fired up. I then removed the external power supply and the set remained on. Next, I switched the set to standby and then on again and it still worked. I repeated this many times until suddenly it wouldn’t start again unless an external power supply was connected to the 9V start-up rail.

What was going on? My assumption was that this rail was too low for a successful startup sequence but after installing new diodes (D6635 and D6632) and several new electrolytic capacitors and getting nowhere, I decided to try a different tack. It was time for the hot and cold treatment, so I began by hitting the usual suspects with freezer to see if this would pinpoint the problem

Now, I might add at this point that when the set did start on its own, the 9V rail was actually closer to 10V. It definitely wasn’t low, so I couldn’t help feeling this was a red herring. Anyway, it was while I was alternately freezing and heating components near the rear of the flyback transformer that I noticed the problem suddenly become more critical – like a doctor or dentist finding a sore spot on your body or mouth.

Anyway, it seemed to me that the culprit was D6624. My circuit showed this to be a 4.3V zener diode but in actuality it was an 1N4148. I then realised I was looking at the wrong circuit diagram because in fact the set was GRI-AX version 2. I replaced the diode anyway and a few others nearby but the trail was becoming cold again.

More soak testing was required before the fault re-occurred two days later and I repeated the hot and cold treatment. By now, I was beginning to realise that if the line drive signal was insufficient on startup, the set would not turn fully on. This might also be due to a lack of gain in transistors TR7521 and TR7523.

I replaced the latter first with a BC547C, the original being a BC337-40, but it made no difference. By now the set was again in one of its "let’s play dead" modes. I then replaced TR7521 (a BC368) with another BC547C, making sure that I bent the base lead around the collector lead to fit the leads in the correct holes.

This time the set switched on perfectly. I measured the old transistor to find its collector-emitter junction was very leaky. I was delighted to have at last found a real faulty part and left the set to soak test with repeated on/off switching for the next week before returning it to Mr Sorensen.

Sunk by friendly fire

A good friend of mine is an Australian of German extraction and is a fine technician, working for the local Sony agency. An English client brought his Sony DVP-S735D DVD player in, complaining that the disk drawer wouldn’t open. My friend showed him how to open it by pushing a lever underneath to release the drawer. The client did this but when he put the DVD back in, the drawer jammed shut again.

My friend finally booked the unit in and examined it in the workshop. First, he noticed that without a disk in it, the drawer would open and close by itself quite normally and without duress. However, when the DVD was put in, the drawer jammed. The DVD played perfectly and did all the trick functions – it just wouldn’t release the disk.

My friend removed the covers from the machine and tried to see what was happening. He could see the disk go in OK, the spindle locking magnets clamp in position and the laser focusing as the disk started to spin. All was fine, until he hit eject. The spindle locking magnets opened but instead of releasing the disk, the DVD was being held by the top magnet and was preventing the door from opening.

It looked as though this particular DVD was magnetic! He tried half a dozen other DVDs and CDs and none of them gave any problem – it was just this particular DVD.

And the name of the movie on this DVD? – it was "U-571". Talk about being sunk by friendly fire!

Now, I thought this was a damn good story – but there is a twist. My friend went home that night after fixing it and thought about it. In the end, he just couldn’t believe that the DVD disk could be magnetic – it stretches one’s credibility just too far. So the next day he went back to the set and re-examined the facts.

The DVD player could play any other DVD/CD except "U-571". What about trying it in another player? He did that and found that it would play on other machines, thus exploding his original theory – almost every other player uses the same magnetic clutch mechanism. So why wouldn’t "U-571" play on the Sony machine?

Very careful examination under a magnifying glass showed there was a very fine film of "gunk" on both the DVD disk and the metal plate it was sticking to. The two surfaces were almost analogous to a 2-part epoxy glue. By cleaning both surfaces very carefully, he was able to then play "U-571" on the Sony machine without it sticking to the magnetic metal plate.

So I guess the answer is obvious – always keep it clean!

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