I hate servicing rear projection TVs. It’s not because they aren’t interesting. Rather, it’s because 90% of the repair is spent in the logistics of handling their enormous bulk and because, until recently, their performance was rather "ho hum" (although that’s changed in the last few years), their main advantage being their large picture.

I positively refuse to do in-house service unless it is only a fuse or installation problem. After all, the chassis is at the very bottom of these monoliths and access is usually quite difficult. What’s more, there are usually about one million screws holding the chassis so it won’t fall the few centimetres it is above the ground and smash into a thousand pieces all over the floor.

To make matters even more difficult, the PC board tracks are on the underside of the chassis – at least in a car you can lie on a trolley and wheel yourself underneath or raise it on a hoist!

Items Covered This Month Sony KPE41SN11 rear projection TV set (RG-1 chassis) Toshiba 43N9UXE rear projection TV set (S99SS chassis) Panasonic TX43P250 rear projection TV set (EURO-7VP chassis) Pioneer VSX-D503S 110W Surround Sound AV receiver Lost PIN For A Car Radio

An ailing Sony

Anyway, Mr Hodges 1996 Sony KPE41SN11 rear projection set (RG-1 chassis) was in the process of failing to proceed. Intermittently, the picture was slowly getting duller and now there was no vertical deflection. This latter fault can often be extremely serious because if the protection circuit doesn’t cut in, screen burn will result in just a few seconds and ruin the expensive picture tube. This time, we were saved because the picture was so dull.

Because of the possible danger to the individual tubes, I decide to tackle the vertical deflection problem first. On normal TV sets, the vertical output IC is usually located not far from the line output stage and flyback transformer. And because the service manual for this set was on order, I thought I would have a crack at it blind.

I began by "wedging" the projector between the ceiling and the top of my work bench (it’s possible I might be exaggerating just a little here – but you get my drift!). And because it took up so much space, my soldering iron and all other tools had to be moved onto nearby stools.

Even after removing the million or so screws (again, I might be exaggerating a little), it was extremely difficult to edge the chassis out, as the cable harness is tied down tightly to the cabinet in several places. In the end, I gave up and instead decided to remove the board with the flyback transformer (I later discovered that this is the E Board).

This was a bad choice as it didn’t really have anything to do with the vertical output. However, having removed it, I resoldered a few potential dry joints and checked the fusible resistors and anything else that looked as though it might throw a spanner into the works. I then refitted the board and moved along to the next on the right – the A board. In fact, on later models, this is the board with the vertical output IC.

Removing this board wasn’t easy. First, another one million screws had to be removed and I also had to dissect and remove the AV-inputs board (U) and unplug the processor board B which fits across the A Board. This was tricky for two reasons: (1) there was no headroom; and (2) it was fastened to a sub-frame that had to be unscrewed, not to mention that the main plug had a child-proof lock on it which I couldn’t work out.

Eventually, however, with the aid of a lot of muttered words like "bother" and "drat", I managed to force the boards out, only to discover that what I thought was the vertical IC was in fact the sound output IC. Again, I resoldered everything and then spent a large part of what was left of the rest of my life putting it all back together again.

By now, the 140-page Service Manual had arrived and I soon discovered on page 79 that the vertical IC (IC1501, STV9379) was on Board D, somewhere near the front of the set. And so I stuffed the main chassis back into the case and turned the workshop around to get to the front of the set.

The D Board turned out to be on the floor pan, behind the HA Board and just in front of the three CRTs. Fortunately, this board is quite easy to move. Once again, I checked for dry joints and also fuses F1601 and F1602 and fusible resistors R1519 and R1520 which supply the ±15V to the IC. Unfortunately, nothing looked crook, although that was the way I was starting to feel.

Anyway, I replaced the board and switched the set on to find that it was now dead, with just the front LED flashing. So what had I done?

It was time for a new tack – when in doubt, measure the B+ but honestly, why don’t I follow my own advice sooner rather than later! This was a good move because the ±135V rails were way down to just over ±100V.

There was a good chance this was where the fault lay. I removed the board and worked on it separately on the kitchen table.

Next, I removed plugs CN6011 and CN6009 on the power supply board (board G) to eliminate any possible loading effects and hung a 100W globe across the positive rail. It was still low, however, and even the ±15V rails were low, which probably accounted for the set’s lack of vertical deflection.

A few checks showed that the correct voltages were being fed into the board and the "sub power supply" (STBY) was OK too. I then checked the +135V feedback via IC6008 (SE135N) and optocoupler IC6006 and this was also OK.

It took another eon of time for me to finally discover that the culprit was 270kW (4W) resistor R6010, which had gone high to the base of Q6001 (RECT OUIT SENC SW). This was surprising, as it is in series with another 270kW resistor (R6009) which was perfectly OK from the main +330V rail from the bridge rectifier. However, this biases the drive to Q6009 and the drive control to IC6009 via optocoupler IC6005.

Anyway, this actually fixed all the symptoms this set had and the picture and sound were pretty good. I really earned my money on this one!

As a postscript, when I got the manual, I also received a Sony Service Bulletin (AVS167 – 1998) about a fault with this symptom: the "top screen has a brighter band effect noticeable on dark screens". It suggested changing C289 at pin 1 of IC208 on the dreaded B Board from 4.7mF to 22mF (Part No: 1-128-551-11), so at great risk to what was left of my sanity I replaced that component as well.

I do hope that Mr Hodges appreciated my efforts.

Other rear projection sets

Other similar dramas I have had recently with rear projection TV sets mostly concern the same logistics problems. However, the faults were different.

One of the sets involved was a 1999 Toshiba 43N9UXE (S9SS chassis). When the "on" button was pressed, the set would try to come on and you could even hear the rush of static from the EHT. However, that was as far as it would get, the set then shutting down again.

This was eventually isolated to R347 (180kW), which had gone high on the Deflection Board and which feeds a protection circuit involving Q340 and Q341. This circuit monitors the 200V LVP line from the CRTs. In addition, a 36V zener diode (D878) in the 30V power supply for the protection circuit was leaky.

The other set was a 2001 Panasonic TX43P250 (EURO-7VP chassis) with an unusual North-South pincushion correction fault (as opposed to East-West), plus intermittent lack of horizontal synchronisation. Fortunately, we had another identical set in at the time and were able to substitute boards.

This second set had a burn spot on the green tube. A possibility here is that the vertical output IC (IC451) and the two convergence amplifiers (IC7001 & IC7002) had spat the dummy on the D Board but if so, why hadn’t the other two tubes been affected? A more likely explanation was that someone had left both the vertical and horizontal deflection yoke outputs disconnected on the green CRT. I have my suspicions.

Getting back to the first Panasonic set, I started with the vertical output and convergence boards, which are the most common areas for failure, but no luck there. Next, I tried the A Board and it wasn’t that either, nor was it the DG Digital Module.

Eventually, I found that the problem was on the U Board (TNPA2042AU) which carries microprocessor IC1101, flash ROM (IC1102) and SDRAM (IC1106). The EEPROM (IC1104) is on the A Board which was OK.

I really should have guessed sooner as there was no on-screen display (OSD) and the data was being corrupted. Unfortunately, this expensive little module is no longer available, however hopefully it was only the flash ROM that was at fault.

Being a Panasonic agent, our technical officer told us we could either replace the 8M-Flash ROM IC1102 (marked TV RJ646-4 on a white label), or he could come around and upgrade the firmware.

We settled on the latter. The firm-ware upgrade deletes the flash settings (which are the non-specific model information such as aspect ratio, progressive scan, SD/HD options, etc) and then reloads the default values. The geometry and convergence settings and levels are kept in the EEPROM.

Anyway, to do this, the set has to be put in the service mode and a special interface from a notebook computer connected to composite video inputs AV2 and AV4 on the rear of the set.

To get the set ready, we had to perform a number of functions blind as we had no on-screen display. After switching the set on, the SETUP mode has to be selected on the remote control and the OFF TIMER set ON to 15 minutes. You then exit SETUP and press FUNCTION on the TV. Finally, you press and hold VOL- on the TV and RECALL on the remote, then press STR (store) on the remote until you can hear the relay click in.

This relay switch-es the AV2 and AV4 inputs to allow serial DATA directly into the main microprocessor on the U Board.

That done, we ran the upgrade utility on the computer which at least tells you what’s going on. This took about five minutes, after which we switched the set off and then on again. It came back on with a perfect picture and sound, so the upgrade fixed the problem – well, nearly. Ten minutes later, the picture began tearing again but we audibly traced this back to the flyback transformer which was intermittent and probably the cause of the whole problem.

A new one finally fixed it.

A cow of a fault

Sometimes you just can’t do anything right! Dave, our ace audio technician, had a cow of a fault just the other day.

He was given a 1994 Pioneer VSX-D503S 110W surround sound AV receiver with an intermittent crackle in the left channel to repair. Now, our Dave is normally a very cautious sort of guy but he reckoned he knew what the fault was straight away. In particular, he suspected the differential input transistor pair Q01 & Q03 in the power amplifier stage. After all, the fault was independent of the volume control setting, which ruled out the preamp stages.

Being a caring type, he usually uses a cotton bud which he sprays with freezer and then just touches the suspect component. However, on this occasion, he must have been having a bad hair day – not that he has much left! Anyway, he hit the transistors directly with the freezer. Well, oops – output transistors Q1 and Q3 lost their bottle and failed instantly. He replaced them and the differential input transistors and when he switched it back on, it was fixed. However, when he turned it off and then back on again, it wouldn’t come on.

Would you believe that the microprocessor had failed? Apparently, this can happen due to transient pulses when the power transistors fail. Data was going in but nothing was coming out. And so a new IC801 costing in excess of $200 was back-ordered (ETA four weeks). When it finally came, Dave fitted it but now found that the protection circuit was cutting in.

After spending yet more time, he found that Q608 was short circuit but the set still refused to fire up after it was replaced. However, he could turn it on by shorting Q604’s base to its emitter.

Feeling somewhat cheesed off by now, Dave replaced Q602, Q603, Q604, Q605, Q606 and Q608 to save time and switched on again. However, it wasn’t Dave’s day – or even his fortnight! The sound was OK at low volume but at high volume, was distorted in the left channel. He checked this with the CRO and after a lot more time than he would care to admit, he located the little !@#$% – it was R525, a 100W resistor which had gone high. This finally fixed the last problem.

The annoying thing was that these were all unrelated different faults, occurring one after the other. I guess the good thing was that at least they happened while he was still fixing it – it would have been much more difficult had they failed during the warranty period.

No wonder the poor bloke is losing his hair!

The next story comes from a mate who works in the automotive industry. I’ll let him tell it in his own words.

Lost the PIN?

One of the most annoying features of modern car audio systems is the use of the "PIN" number. Actually, this is a tautology – it really is just "PIN" of course, otherwise you would have a "Personal Identification Number Number".

Anyway, there was a time in the 80s when the high-end model cars from some manufacturers were fitted with the very best audio technology. Some units were very elaborate affairs, with Dolby, 4-channel outputs, graphic equalisers, digital displays and more buttons than the control console on the Space Shuttle. Remember, this was 20 years ago!

Problem was, because they were so good, they attracted low-life car thieves with amazing regularity. The security systems on cars back then were almost non-existent and most vehicles could be entered using a comb or a piece of plastic tie-strap. And quite often, the thieves did more damage to the car, especially to the dash facia, while removing the audio gear than the gear itself was worth.

In many cases, the gear was literally hacked (or even chopped) out.

To prevent this, the manufacturers introduced the idea of a security PIN for their top-line audio units. This was very effective – as soon as the 12V (memory) supply was removed, the unit was transformed into an expensive paperweight – unless you had the PIN, that is. If you didn’t know the PIN, it was impossible to get the unit working again.

This proved very effective and dramatically reduced the theft of high-end car audio equipment almost overnight. As a result, all the makers jumped on the same bandwagon and PIN systems are now used on even the most basic audio system head units. This and the fact that good-quality new systems can be had for a portion of one week’s wages have made car audio theft a redundant industry.

Anyway, this is all background to a problem faced by the writer following the purchase of a secondhand car, a Daewoo Nubira wagon. The car itself suits our situation perfectly – the right size, good performance, equipment, economy, etc – but most importantly of all, the purchase price was too good to pass up.

The standard fare in the audio department was an in-dash AM/FM CD player but unfortunately, the PIN had been misplaced. The reason was quite simple – early in the car’s life, the CD player gave up the ghost, during the warranty period, so an attempt was made to repair it. However, as with many such units nowadays, the necessary parts were either unavailable or too costly (or both), so a replacement factory unit was fitted and everyone was happy.

Well not quite, the PIN was not recorded by either the dealer or the previous owner, so when we fitted a new battery several years later, we were greeted with deafening silence and the word "Code" flashing on the audio unit’s display. Unfortunately, despite a thorough search of the dealer’s records and other material, no PIN was to be found – a task made doubly difficult by the fact that the car was originally sold new in WA.

So that was it – the existing unit was literally junk. The only solution was to buy a new head unit, an easy task I hear you say. Well, not so! We needed a new unit to not only receive AM & FM and play the occasional CD but also to suit the dashboard.

It also had to be user-friendly. Many units have multi-coloured, hard-to-decipher fluorescent displays and buttons so small that they cannot be read or easily pressed.

The most common facia colour is now silver, whereas the most common look five years ago was black – not a good look. Without being too old-fashioned, it would also be nice to have a rotary volume knob and large easy-to-find controls for the major functions. Swapping, as I do, from car to car, it is quite often near impossible to turn some unfamiliar units on or off, or tune to a different radio station.

To cut a long story short, a suitable unit (at a suitable price) was eventually found. The next step was the installation.

Without going into detail, the dash-mounting method was very well designed – much better than some of my previous setups where you had to be both a double-jointed contortionist and adept at plastic welding repairs in order to fit a simple car audio head unit.

Wiring is another area where things have improved immensely with time. It’s now possible to purchase plug kits that are compatible with the dash harness plugs but some are so unique that they fit only one manufacturer’s models and then only from one particular year! It seems that some automotive designers go to great lengths to make otherwise simple tasks overly complex, perhaps for no other reason than to justify their job status within their company!

Anyway, the wiring was straightforward for the most part, with the speaker wiring arranged in four pairs utilising standard colours. Unfortunately, though, we ran into problems with the wiring format for the display dimming.

In the original factory unit, display dimming is achieved with an earth return through a rheostat, with the 12V supplied by the same accessory supply rail that powers the unit. However, without access to the factory wiring schematics, the job was just too difficult. In the end, we had to do away with the dimming feature, as the new unit did not allow for this strange set-up.

With the task now complete, we could sit back and admire both our handiwork and how well the new unit’s easy-to-read, large, green display almost perfectly matched the Daewoo’s instruments. All this for the princely sum of $150.00, including the plug adaptor kit.

The stacker

Being even more adventurous, we found that the maker of our new system also had available a magazine-style 10-CD stacker that mated perfectly with it. This is where sadness enters our tale. We ordered the stacker but when it arrived, we found that its packing had been tampered with and that the transit screws were missing. The reason given for this by the retailer was that there weren’t many of these units left and this one had been "pre-tested". What they didn’t tell us was that this unit did not pass the test – the CD stacker failed to "stack" or do anything else bar emit some very odd noises.

We also found that the number of such units left in Australia was just one – this one! Anyway, we now look forward to a 6-week wait, while their "service department" investigates the matter.

Why is it always a long wait when the item in question was needed yesterday as a surprise for Mrs Serviceman’s birthday? There’s no point investigating this in our own workshop, since we lack the necessary parts and service information – not to mention voiding the warranty.

All we can do is wait and see what happens.