Items Covered This Month Philips Matchline 33FL1880/75R TV set. Panasonic "Progressive Wide Plasma Displays" (Model TH-42PWS) - installation. Akai TX-140 stereo unit. JVC AV-21 TEAU TV set (MZ2 chassis). Faulty remote control.

I can't help myself. Yes, I did it again; lumbered myself with a repair that I should have stayed well clear of. But I did have some mitigating circumstances.

It's my wheels. Because I'm so badly paid, I have to use secondhand vehicles and my old Ford Laser was just about to dump its gearbox. Ouch!

Anyway, I was sulking over this latest problem one morning when in waltzes an old colleague. And in the ensuing conversation, he mentions that he is trying to fix a Philips FL1.1 with an east-west pincushion fault. I told him to wash his mouth out for mentioning such words in my presence. But grateful that it was someone else who was suffering from such misfortune, I offered as much free advice as I could - as long as he was doing the work.

That is, until it turned out that his client was a Ford transmission expert and repairs them all day long. Suddenly I realised that a dangerous contra deal was in the air but I quickly lost all sense of reasoning. I mean, how bad can a TV fault be? And after all, I could end up saving many hundreds of dollars.

In due course, my car went east and his TV set came west; straight into my workshop. And being a 33-inch (80cm) set, I almost had to rebuild the workshop around it to get it to fit.

The set turned out to be a model 33FL1880/75R, the same as one I wrote about in last month's issue. This set had the same problems as the one in that article and my friend patiently worked through it until, finally, he too discovered that capacitor C2523 (8.2nF, 2kV) capacitor was the cause.

He then replaced all the blown up bits and that fixed everything except the east/west fault which had him stumped. I had hoped for a minute that it was just transistor Q7610 (2SA1359) that was faulty, as in the earlier set, but he had already changed that.

Anyway, I own two working FL1 TV sets and another which also has an east-west pincushion fault, though none of them are 33-inch models. I checked all my friend's work first and apart from replacing the horizontal output transistor ON4673 with a BU508A (a BU508AF is an even better choice), nothing apart from a few faulty joints was obvious. However, the voltage on the emitter of Q7610 was only 1.8V instead of 14V and neither the width adjustment (VR-3601) nor the pincushion control (VR3602) had any effect.

I had heard that shorted turns in coil L5526 could cause this fault, so I swapped this coil with the one in the good set. Unfortunately, it made no difference to either model and both coils had an inductance of 11mH.

I then decided to try similarly swapping transformers 5521. This turned out to be a monstrous mistake, as it instantly took out both horizontal output transistors. After replacing these, I still couldn't get the set to start and there was no 141V rail. Eventually, after a lot of messing about, I discovered that Q7610 was short circuit but the set was still dead when this was replaced.

Next, I unsoldered pin 8 (141V input) to the horizontal output transformer and horizontal output stages and fitted a 100W globe across the rail instead. This time when I switched it on, there was an enormous bang, like a shotgun going off. Believe me, it was loud enough to have awoken the New Zealanders.

Well, at least I had produced a measurable reaction - a small earthquake! The only trouble was I didn't have a Richter meter to measure it!

In fact, it was C2512 in the horizontal centring circuit which had exploded. It took quite a while to realise that Q7512, Q7513, R3514, R3537, R3515 and D6515 had also been destroyed. When I finally put it all back to where I started, I made an emphatic mental note: not all FL1.1S chassis are the same and not everything is interchangeable.

However, the east-west circuits are similar and therefore the voltages and waveforms between the sets should also be similar. As a result, I spent an hour or so measuring the good 29-inch set's east-west correction circuit voltages and drawing the oscillograms.

As I have mentioned on previous occasions, access to this chassis is rather difficult. The so-called service position is with the main chassis (small and large signal panel) pulled right back and up. You then have to balance it on its edge, taking care not to short out the CRT socket with the heatsinks. The control panel and mains filter panel remain behind.

The chassis is bulky and heavy, with modules and heatsinks everywhere - mostly soldered in. The voltages in some parts are very high, with sensitive surface mounted components nearby. Replacing a part requires access to both sides of the board, which means moving them up and down.

Finally, just to make life interesting, the 315V main HT line remains charged even after the set is switched off - not to mention the 200V rail for the RGB output amplifiers. And because the whole chassis is precariously balanced in the "service" position, it's impossible to safely attach a probe onto a subminiature component and take a reading.

It's also impossible to make any service adjustments while in this service position, as the controls are all on the inaccessible side of the board. In fact, even in the so-called "accessible" position, they aren't easy to get at! For example, to measure and adjust the 141V rail, it's necessary to attach the probe onto test point TP57 (cathodes of D6237 and D6238). What they don't tell you is that these sit right between a heatsink and the SOPS module and there is very little clearance between these two parts.

In practice, it is necessary to go to standby, connect an insulated crocodile clip onto the diode, then switch on using the remote control and adjust R3371. And you really have to watch yourself: one third of the large signal panel is at full mains potential and the other two thirds is at chassis - and the dividing line is not easy to see. No wonder no-one likes fixing these beasts.

Basically, the east-west circuitry converts vertical pulses derived from the vertical deflection output into upside-down parabolas. These are then fed to the east-west output transistors which in turn drive one end of the deflection yoke via a variety of tuning components. The other end of the deflection yoke is fed with 1000V horizontal pulses. EHT information is also applied to prevent picture blooming on bright screens.

The preamplifier stages consist of four surface-mounted transistors which are controlled by the width and pin controls. Unfortunately, the circuit diagram is full of errors, with few voltages and waveforms.

I replaced all the surface-mount transistors and all the electrolytics but the fault persisted. Despite that, the two sets compared quite well, although factors such as the control positions, the size of the sets and the beam current due to picture content made it difficult to work out what was important and what wasn't.

The main factor was the voltage on the emitter of the east-west output transistor (Q7610) which was constantly far too low. The breakthrough came when I noticed that one of the east-west modulator diodes, D6526 across the horizontal output transistor, went to C2504 and not to the emitter. I also noticed a thick black jumper lead across the two emitters of Q7504 and Q7506. However, this lead was unnecessary because they already had a link on the other side.

Granted, it's not uncommon in TV sets to have what may be considered redundant links. Sometimes it's because there is high current and sometimes it is to limit inductance. However, the link was not fitted in the 29-inch model, so what was it's purpose?

There seemed to be no reason - unless the link was in the wrong place. Could it be that, in the course of changing the horizontal output transistors, my friend removed the link and put it back in the wrong position?

Well, of course, it was in the wrong position. Both C2504 and D6526 weren't connected properly into the circuit - and rerouting this link quickly fixed that.

But I wasn't quite out of the woods yet. The east-west controls now had an effect but not enough. The voltage on the emitter of transistor Q7610, which was previously too low, was now too high - at times nearly 60V!

More careful examination revealed that R3611 (2.7kΩ) and R3614 (1.5kΩ) were both high. Replacing them brought both controls within a tolerable range.

Finally, I replaced the back and left the set on soak test. I hope that its owner has done as good a job on my transmission!

Plasma sets

My next story is not, strictly speaking, about a conventional service job; rather, it was an installation job. More exactly it involved installing two Panasonic "Progressive Wide Plasma Displays" (Model TH-42PWS). These are very large units, measuring 1020 x 610 x 89mm (plus the speakers), and are designed for wall mounting using special brackets.

It needs at least two people to safely manhandle these monsters, since the total weight (display and speakers) is 32.7kg. The special wall-hanging brackets (TY-WK42PV1) that are used to support the display are made of heavy-gauge steel and weigh a further 6kg each!

Panasonic recommends that the brackets be mounted using at least six bolts but I fitted 12 just to make sure. After all, plasma displays don't take too kindly to a fall, this being the most common reason for failures.

The first thing to do was work out the optimum height for the display (in most cases, eye height) and then drill one hole at top centre to hang the bracket. The bracket is then initially attached using a single M6 bolt, then adjusted with the aid of a spirit level and used as a template to drill the holes for the remaining bolts.

It was also necessary to mark a cable access hole on the bottom lefthand side. This hole (30 x 100mm) needs to be drilled right through to the brick cavity in order to accommodate the cables. Another hole then has to be drilled where the cables are to emerge and connect to the associated AV equipment - VCR, DVD player, digital set-to box, amplifier, etc.

I was annoyed that most of the accessories were not immediately available from Panasonic and I hope they will fix this soon. For example, I wasn't able to get the TV-PT600E (and TY-42TM5H, TY-SCP15C03, TY-42TM5T) tuner/receiver. Instead, I had to use an existing NV-FJ630A hifi VCR as the main tuner.

One of the display units had to be fitted across a corner, which I thought was a waste. However, that's what the customer wanted and he was paying.

To do this, we made up a solid metal panel which was bent over at 45° at each end and mounted vertically in the corner. We used 2mm-thick aluminium for this and I was initially worried about its rigidity but when the set was mounted, it was very solid.

I also fitted brackets to hold and conceal the VCR, which I modified so that the infrared remote control receiver was external and just peeping over the top of the display. Interestingly, I found it to be more sensitive facing the wall than looking back out towards the viewer.

When it was all finally connected, the digital reception was exceptionally good. Overall, the effect was fantastic. I just wish I could afford one!

Akai TX-140 stereo unit

A young woman brought in her Akai TX-140 stereo unit with the complaint that it wouldn't play CDs. As sometimes happens with these types of systems, I was expecting that either the laser and/or the disc motor had failed. In the former case, the disc starts to spin and the laser comes on and tries to focus. If it fails to read, the CD stops.

I removed the top cover to watch what happened and found that the three CDs on the carousel would not stop rotating around the platter. What's more, they would not line up with the CD reader.

I prised off the platter and saw how the deck worked. Each disc had a series of plastic tongues on the underside of the platter, one for disc one, two for disc two, etc. These gave a digital pulse as they passed between an optocoupler. What was fairly obvious was that the optocoupler wasn't working.

The optocoupler is mounted on a small board with a 5-strand flexi-lead between it and the platter motor. The flexi-cable seemed to be the obvious culprit and I checked the continuity with an ohmmeter. As I suspected, two of the conductors were open circuit.

I tried repairing it by running a parallel wire with flexi-cable but it wasn't possible to solder it on, so I ordered a longer generic flexi-cable.

When this arrived, I cut it to size and stripped back the insulation about 2mm to solder onto the sub-board. Because of its size and the heat of the iron, it was quite difficult not to make a complete mess of it but with a bit of perseverance, I finally managed to solder it on. The reassembly was a breeze and the job was done.

JVC TV set

When a rather ordinary-looking 51cm JVC AV-21 TEAU (MZ2 chassis) was brought in, I wasn't really expecting anything other than a mundane repair. The set was dead and it didn't take a mental giant to figure out that the horizontal output transistor (Q522, 2SD1878-YD) was short circuit.

The only replacement I had was a 2SD1878, which wasn't fully isolated like the original but this was easily fixed with a mica washer. However, when I switched the set on there was a split second during which the normal static field around the picture tube was very much higher than normal. As I say, it was only very brief, then it was back to square one.

But while it lasted, the effect was so great that I received a shock and there was also a flash-over inside the picture tube. Initially, this made me think that perhaps the picture tube was down to air. It took another transistor failure to prove it wasn't the tube, as I had totally disconnected it by then.

The most common problems that can cause horizontal output transistors to cark it are: (1) a faulty horizontal output transformer; (2) a faulty deflection yoke; (3) excessive HT; and (4) crook tuning capacitors - although not necessarily in that order.

I unsoldered and measured tuning capacitor C524 as well as C525, but both were spot on. I then removed the deflection yoke and examined it carefully but it too appeared to be OK. I also reworked the solder on the motherboard but no joy.

Unfortunately, my copy of the service manual didn't have the circuit diagram or service adjustments for this set, which was extremely frustrating. I did have the circuits for an AV-G21AU, which is a CA2, and an AV-G25AU, which also uses an MZ2 chassis, but neither was quite close enough.

I assumed that the HT (B1) rail, at test point TP-91, should be at 114V. To confirm this, I had to replace the horizontal output transistor, short out its base and emitter and connect a 100W globe. It was spot on at 114V.

So all that seemed to be left was the horizontal output transformer. My shorted turns tester could not detect any shorts across pins 9 and 10 but that doesn't mean very much; high voltage failure in the secondary can't be detected at low voltage.

Finally, I ordered a new horizontal output transformer, confident that that was it. However, after fitting it, the set behaved exactly as before and then died.

I can't lie that I was the great brain that discovered the cause of this one - instead, it was Technical Support at Hagemeyer.

Though I thought I had been completely thorough in resoldering everything on the motherboard, I had in fact neglected to check and resolder the connection to the horizontal oscillator ceramic resonator/crystal (CF-561) on pins 14 and 17 of the jungle IC (IC201). And that was what wrong with the set in the first place, causing it go wildly off frequency and the EHT to rise spectacularly.

After realigning the yoke and CRT p/c magnetic rings, everything was fine except for one slightly bizarre problem. I didn't have the remote control but I noticed that by pushing the channel (CH) up and down buttons on the set itself, I could select "AV" input. The problem was that the video from my signal generator wasn't going in via the AV sockets at the rear.

Conversely, I could tune it in when I plugged the generator into the antenna socket while still in the AV mode.

Initially, I thought that the AV switching ICs had failed, along with a transistor controlled by the microprocessor. Later, when I read the instruction book on this model, I learnt that it is necessary to select either "TV" or "Video" with the remote control to change the source. The "AV" mode in this set really just denotes the change in sync time constant that is required to prevent "flag waving".

Now, on a lighter note, here is a contribution from K. A. of Kingston, Tasmania. This is how he tells it.

Unreliable remotes?

A friend had been grizzling on and off over several months that all the remote controls for her new and expensive TV, DVD, and VCR were unreliable. The problem wasn't so much presented as "It's busted, will you fix it?" but during dinners as part of idle chit-chat about growing old and coping increasingly less well with new fangled gadgets.

It took ages for the various bits of information to completely emerge. Apparently, the batteries in the remotes had been replaced umpteen times, the gadgets had been taken back to the shop umpteen times (they were still under warranty) and experts had visited umpteen times. Furthermore, red herrings like too much sunlight, too much light in general, interference from modern high efficiency lights, etc had all been eliminated.

There was some hazy information that the various remotes weren't all equally unreliable. However, the details were confused and this information was no help at all.

One day, a really weird piece of information emerged; the remotes all worked well for my friend but not for her teenage son. Now if this had been the other way round, it wouldn't have been significant; teenagers often successfully use gadgets that have adults baffled.

Lacking any solid clues, I continued to offer sympathy rather than useful advice and left the problem as one of life's little puzzles. And then one day, I was visiting their home while the teenage son was watching TV and wrestling with one of those (expletive deleted) remote controls.

Aha! Problem solved!

Have you seen the way teenagers sit in chairs to watch TV?

His feet were on a footstool, his backside was dangling over the edge of the cushion, his back was where his backside should have been and his head was propped up against the back rest. Bone surgeons will make a fortune 30 years from now reconstructing his neck!

But that's not all. The remote control was on his tummy and his great big size-15 feet were between it and the IR sensors on the TV, VCR and DVD!

IR light doesn't shine through feet! - no wonder it wouldn't work.

The equipment itself was installed in a typical cabinet with the VCR on the bottom, then the DVD and the TV on top. The TV could occasionally get a glimpse of the remote control over the teenage son's toes and so it worked sometimes. By contrast, the VCR was in a deep, dark, gloomy shadow and almost never worked!