Items Covered This Month Pipe locator Technics SP-10MkII-XAL direct drive turntable Philips 21PT2302/79R TV set (L01.1A chassis) Philips 900 series TV set (KS685 KL9A-3 chassis) PanasonicTX-86PW100A widescreen TV set Akai VS-G875EA-D VCR Nakamichi Soundspace SS-11 home theatre system Teac EU-68ST-1 TV set employing an 11AK37 chassis.

One interesting device I was recently asked to fix was a commercial pipe locator, as used by local councils. This consisted of a 33kHz/8kHz transmitter and a radio detection wand receiver. This device basically looks for signal induction in pipes, as well as in power cables.

The only trouble was that this particular unit didn’t want to oscillate. As I quickly discovered, the unit is supplied by a 5V source but this had dropped some 20% to 4V. But although being a helpful clue, the question was whether the power supply itself was faulty (and so couldn’t deliver the power required) or was it the load that was giving problems and dragging the supply down?

A cursory inspection of the AC/DC power supply didn’t reveal any clues and the circuit diagram supplied was a nightmare to interpret. Anyway, I decided to first check the load option and began by disconnecting the 5V rail to each of 20 ICs (by breaking the Vcc track). When I did this, the 5V rail gradually recovered as I disconnected more and more of the ICs, as you would expect. However, one IC that was isolated had a dramatic effect, with the rail jumping by nearly the full volt!

Delirious with joy, I ordered the IC and when it came, I couldn’t wait to install it. However, it made no difference! Bummer!

I had isolated this particular IC by removing a jumper link but on inspecting the double-sided board more closely, I noticed there were some surface mounted capacitors on the same rail. These were all found to be resistive and it turned out that it was these components that were causing the 5V rail to drop to a level where the oscillator wouldn’t work.

I removed one of these capacitors and measured it out of circuit but could find nothing wrong with it. I then did the same with eight other surface-mounted capacitors which were hung off the 5V rail and again none measured faulty. However, the unit was now working.

So what gives? Well, it took a little while for the bell to toll for this idiot (I must be an idiot to work in this profession!). It was actually the cement (or glue) that was used to fit these surface mounted components to the board prior to soldering that had become conductive. Desoldering and removing the components had also melted or destroyed the glue link, so the circuit came good.

Cleaning the board and refitting the capacitors fully restored the unit to full working order.

The old turntable

The Technics SP-10MkII-XAL is a professional quartz phase-locked direct-drive turntable which, I believe, cost about $4500 20 years ago – and the tone arm was extra! As a matter of interest, its claimed speed drift was within 0.002%!

The one that came into the workshop was, I was told, an ex-ABC unit. And it had an unusual fault – when switched on, the turntable would sometimes go backwards! Still, that’s ideal for Rap music, in my opinion.

These decks use an external power supply (SH-10E) in a separate box, the connection being via a canon plug which supplies +5V, +32.5V and 140V DC. The owner had managed to borrow another power supply and the deck worked flawlessly with this. However, when I measured the three DC outputs of the original supply, they were all approximately correct under no-load conditions.

Even so, there was obviously a problem with this power supply.

My next step was to compare the two supplies more thoroughly and I soon found that the good supply was 10V higher than the faulty one on the 140V rail. However, both supplies were high on this rail, the rail measuring +156.3V on the faulty unit and +163.2V on the good unit.

It didn’t take long to find that C416 (100μF, 160V) was open circuit in the crook supply. I replaced this, along with a 22μF capacitor on the same rail for good measure. Now both supplies mirrored each other for the 140V output but to my disgust, the fault was still there!

Because the turntable was going intermittently backwards, I figured that this had to be a logic problem and therefore the 5V rail was probably the culprit. Under load, it was dropping to 4.6V, so I investigated this further.

A few quick checks revealed the the collector voltage of regulating power transistor TR404 was incorrect. It should have been at 11V but was down to 9V. I replaced capacitor C410 (1000μF, 16V) which restored the 11V collector voltage and after adjusting R406, I now had a precise 5V output on load.

This cured the fault and I found that C410 had indeed dropped its value. Finally, I replaced the pilot lamp and gave it a good soak testing, just to be on the safe side.

Warranty claims

On the TV front, there have been a lot of warranty claims for consumer related issues. Apart from the lack of height, which I have mentioned before regarding letterbox/16:9 transmissions, we now get a lot complaints for poor sound and incorrect colours on brand new TVs, whether they be from terrestrial broadcasts or AV inputs. Almost all such problems are attributable to incorrect selection of the television system for Australia.

We are CCIR (Comite Consultatif International des Radio-Communications (International Radio Consultative Committee)) System B/G ("B" being for television channels Band I/II and III) and "G" for German UHF channels. Our colour system is PAL-D and our sound system is 5.5MHz and 5.74MHz for stereo.

Another problem is language. If this is set to Chinese, Korean or Japanese, it’s pretty difficult to work out how to put it back to English without a concise instruction booklet explaining the menu system.

Perhaps the manufacturers should universally come up with a common colour code for various menu settings – eg, Australia B/G PAL-D, 5.5, English all in red. Or perhaps you could just select the country or city you are in and the set will automatically select the correct system.

Back to the races

My next job was an Akai VS-G875EA-D VCR which had noise bars at the top of the picture.

I had sold this hifi VCR to a bookie back in 1998 and it had been in almost constant use recording horse races! Apparently, he used the on-screen clock for timing the horses.

Because it has seen so much use, I automatically concluded that the video heads were worn when the noise bars were mentioned. Unfortunately, you can’t buy the heads by themselves – instead, you have to get the upper and lower drum assemblies (including the motor).

Enfield Electronics said they could obtain these parts in about four weeks and I was about to send a confirmation fax for the order when I noticed that the supply guide wasn’t engaging fully home on the lefthand side around the head drum. Examining it carefully, I found some white plastic – presumably from a broken cassette – that had got caught on the grease. Removing it enabled the auto tracking to tune out the noise bars.

Unreasonable customer

Sometimes clients with warranty claims can be unreasonable.

We had one lady with the same model Philips TV who also complained of a faulty AV input and that her son couldn’t play his video games, there being no sound or picture.

She demanded we call out immediately and bring a loan TV. Despite her obvious attitude problem, we could handle all this but I began to get tetchy when she gave me the wrong address for her home and I had to walk a long way with a loan TV to get to it.

She was in no mood to demonstrate the fault but I gently insisted that I had to see what was going on.

She had bought one of those 80 games-in-one units advertised on TV and had correctly connected it to the AVR input on the back of the TV, which she selected with the remote. However, when she switched on the video game, she put the card in back to front. I pointed this out to her, whereupon she proceeded to argue that she knew exactly how to use this game and she was doing it correctly and I knew nothing.

Well, what can you do? Fortunately the phone rang and she left the room to answer it, giving me the chance to turn the game around and plug it in correctly. When she returned, I already had the game running with sound, picture, colour lights and action.

She demanded to know how I had fixed it so quickly, so I gladly enlightened her. She took this with particularly bad grace and then refused to pay for the service call.

In the end, I just picked up the loan set and hiked back to the car. The old crow wasn’t worth arguing with and I certainly won’t be going back there again.

A sickly Philips

A Philips 21PT2302/79R TV set using an L01.1A chassis came in with an intermittent "no sound" fault and poor picture and colour on AV2.

I started by checking whether the correct Australian TV system had been selected and checked the option codes for the set. They were all OK. What’s more, in the SAM mode, there were no fault codes in the error buffer.

I started with the sound problem and, using an audio probe, traced the TV sound all the way to the AV switching IC (IC7801 HEF4052BT), a surface-mounted 16-pin device. I also checked the Vdd voltage on pin 16 to find it was very low and traced that back to R3801 220Ω which is fed from the 8V rail, which was correct.

Fitting a new IC fixed the sound and I thought that if I also changed IC7802 (HEF4053BT), it might fix the picture too as it is such a similar switching IC. Unfortunately, changing it made no difference so that theory quickly bit the dust.

From here on, it looked as though it might get tricky. However, my hunch was that EEPROM IC7602 might have become scrambled, so I changed that as well as it’s such an easy job (only eight pins and not even surface mounted!).

That proved to be a good move as it fixed the AV2 picture problem. I then checked and reset the options where necessary, before soak-testing the set and releasing it.

How or why the faults occurred is difficult to comprehend – perhaps there was a power surge in a storm that scrambled the memory and AV switch.

Lightning strikes thrice

I recently had a 1985 Philips 900 series KS685 with a KL9A-3 chassis come in to the workshop. It had suffered from a power surge during a storm and now had three distinct faults.

First, the TV/AV switch on the front panel wouldn’t switch to AV video. Second, there was distorted sound on mono transmissions. And third, the yellow "Bilingual" LED was on all the time.

The TV/AV switch is a slide switch that indirectly connects 12V to pin 12 of IC7068 (HEF4066). The IC had been damaged and replacing this common analog device soon fixed that problem.

The second problem wasn’t so easy to track down but eventually, by a process of elimination, it turned out to be the stereo decoder IC (IC7791, TDA2795). This IC also controlled the yellow "Bilingual" LED and replacing it fixed both problems.

Interestingly, the two ICs that were replaced are on different boards and these are in different locations inside the set. However, they were the only components damaged during the storm.

Panasonic widescreen TV

I was asked to do a service call on a Panasonic TX-86PW100A widescreen TV set which uses a EURO TauGIGA chassis and an 86cm picture tube.

The set was dead after a power surge and I really didn’t think there would be much chance of repairing it in the customer’s home. These sets are quite complex and if the Digital Board is damaged, the repair job can be an expensive exercise. However, I decided to give it a go in the home because of its weight (86kg) and size (65 x 93 x 59cm), along with its location on the second floor.

When the power to the set was switched on, the indicator LED briefly came on and then went off again. Apart from that, there were no other signs of life.

It’s not easy doing service work on a large, complex set in a confined space. However, I soon managed to establish that there was +5V standby on TPD8 but no +20V, +14V or +144V from the power supply. Nor could I get +376V on TPD6 to the primary of the switchmode power supply.

There was, however, 240V AC from TPD1, D2 to TPD3 and D4, which only left the bridge rectifier (D802). The bridge measured OK and it was R801 (2.7Ω) which connected the negative to ground that had been destroyed – and quite violently. I looked around but couldn’t find any other shorts or problems that might have been associated with this destruction.

As I didn’t have the correct resistor in my toolbox, I hung a 2.2Ω 10W resistor onto the remainder of the original resistor using crocodile clips. I was expecting this substitute to explode just as violently as the original when I switched it on but it didn’t. Instead the set came on, apparently no worse for wear.

In the end, I had to go back to the workshop for the correct part but both the client and I were both happy that it turned out to be so straightforward.

Speaka da Nakimichi?

My mate Pete speaks pretty good Nakamichi for an
Aussie. However, after his 5-day nightmare escapade with a 2-year old $18,000 Soundspace SS-11 home theatre system, he is thinking of taking up Hungarian. This system had been struck by lightning and was for all intents and purposes dead except for the Standby LED flashing.

Pete spend day 1 disassembling the thing and trying to figure out how it was supposed to work. Initially, for the main relay to switch on, there are a series of 5V rails that have to be OK. These are controlled by a central control unit via a 15-pin cable and a digital sound and video processor unit.

Initially, there was no +5V rail due to the $1400 DSB board blowing up. After this had been replaced, the second 5V rail was low. Peter wasn’t sure about the central control unit and had to arrange with the agents to borrow one to check this one out. As it happened, it was OK but he found parts of the power supply had blown – in particular, Q407, Q406 and Q408, as well as U403.

Next, he had to sort out 5V rail No.3 and he traced this to a small regulator (U402) on the headphone amplifier heatsink. Unfortunately, none of this was easy as the component layout diagram is split over a number of boards.

With all the rails now correct, the system would then switch on properly. Finally, he had to reassemble it all and test it. On the sixth day he resteth and so endeth this story.

Dead Teac

I recently had to deal with a 2002 Turkish built Teac EU-68ST-1 TV set employing an 11AK37 chassis. This set was dead with no power and I found that FET Q801 (MTP6N60E) and two diodes – D893 & D892 – had been destroyed. I replaced these, along with the control IC (IC800, MC44608), but the power supply still wouldn’t power up.

I spent a very long time checking out the rest of the circuit before concluding it must be the chopper transformer (TR802) itself. I placed an order for a new one only to be told I was going to be in for a bit of a wait.

The delay wasn’t all that welcome, so I decided to take another look at the set and it was then that I noticed a tiny spark on the secondary winding.

I removed the transformer and found a wire going along underneath it which had been shorting against one of the pins. I isolated this, then replaced the transformer and tried again. The set fired up perfectly!

CD stacker adventures

Paul is a all-round good guy and a highly qualified audio technician whose chief mission in life is to repair CD stackers for cars. It is his job to repair the very popular OEM Matsushita 6-Disc In-Dash Changer Assembly (CQEF7080) CD mechanisms that fit in Mazda, Toyota and Subaru cars, to name but a few car manufacturers.

Just because he repairs so many of these does not mean they are a poorly designed mechanism. Their failure rate is just 0.0028% world wide. Instead, there are other reasons for the failures.

On many occasions, just to appease customers, car dealers have attempted to recover CDs that are "stuck" inside the machine and have ended up ruining the mechanism and PC board. As a result, the entire unit, worth about $1500, has had to be written off.

It’s the CDs which often cause of the trouble. What happens is that when the vehicle goes over a very rough surface and the unit is banged or bumped while changing discs, the CDs are jolted out of position and are not inserted correctly in the trays of the mechanism. This can also happen with copied CDs with labels that can come off and stick inside the mechanism, with the result that the stacker mechanism jams and the trays jump off their correct gears on the white cam. This often results in a cracked CD and the whole mechanism is seized solid.

It’s Paul’s job to strip down and realign the gears and trays, clean and replace any broken parts, reassemble and test. Sound easy? Well, check out the accompanying photo. You can just see the misaligned black trays on the righthand side. There are in fact 371 moving parts and the device is worth about $500 to buy!

Inside a picture tube

Ever wondered what the inside of a picture tube really looks like?

Taking into account the picture size, Sony Trinitron picture tubes are probably the heaviest of all the cathode ray tubes manufactured. And recently, we got the chance to look inside one.

It all came about when a Sony TV set came in with a purity problem on the lefthand side of the screen which couldn’t be corrected. As a result, the tube was replaced under warranty.

As business was fairly quiet that day, rather than simply smash the tube and throw it away, we decided to carefully dismantle it and remove and examine the shadow mask to see why the purtiy was out. This revealed round burn/scorch marks on either side of the Trinitron strip shadow mask (see photo), one being much larger than the other.

Just how this happened is unknown as the client probably wouldn’t admit to what happened. However, it looks as though an intense amount of energy from say a large white dot on a black background caused the shadow mask to distort, giving rise to the purity problems. The reason why the circle is smaller on one side than the other is presumably due to the energy absorption of the shadow mask strips.

The things some people do to TV sets!