Mr Lengel brought in his 1999 JVC AV-P29WH (CD chassis), whinging in his thick East-European accent that his beloved set had died – and it was only seven years old! From the way he carried on, you’d think there had been a death in the family. You’ve "gotta" love blokes like this!

Anyway, his set wasn’t completely dead – it did try to switch on. You couldn’t hear any sound but there was a rush of EHT static and the red and green LEDs were flashing on the front of the set.

Well, at least the +5V rail was OK. The service manual states that there should be 1200V peak-to-peak on the collector of the horizontal output transistor (Q522, 2SD2553-LB) but the oscilloscope showed there was only 800V. What’s more, this transistor was getting hot and there was a smell of burning. There was no sign of ringing on the line pulse and the +15V and +25V rails were OK. However, the screen voltage was down from 200V to just 80V and I suspected that there was something wrong with the flyback transformer.

Unfortunately, I was wrong, as replacing the flyback transformer (a $150 part) made no absolutely difference.

Next, I decided to check the protection circuits and started with Q591, only to find this was an "optional" (OPT) transistor on the circuit diagram. Oh, goodie, we were making progress!

I continued following the x-ray protection circuit and checked Q571, Q451, Q452 and Q981 all the way to pin 18 of microprocessor IC701.

It was then that I struck a clue. A few voltage checks in this part of the circuit revealed that the +12V rail was very low, at about 1.2V. I followed this back to IC971, a BA12T 12V IC regulator which was getting very hot. This device is a low-impedance high-current device and so had to be ordered in specially.

Anyway, much to my relief that fixed the problem and Mr Lengel had his beloved set back again (after whinging about the service cost of course)!

Shrinking picture

I was called out to repair a 2000 Sharp CX-68K5X (NFC chassis) which, according to the client, had a shrinking picture. When I looked at the picture, it was dull, dark and was suffering from horizontal fold over. The line output transistor (Q1830, 2SD2581) was getting hot as well.

From experience, I suspected the deflection yoke and so I loosened it and removed it from the CRT (A68KTB357X034). This clearly show-
ed that the horizontal windings had been cooked and had melted the light-grey former.

I went back to the workshop and made a few phone calls. First, I tried to find someone who might have scrapped one of these sets so that I could buy a secondhand yoke. When that failed, I inquired about the availability of a new one. Apparently they are available and after quoting for the job the client agreed for me to go ahead.

In due course, the new yoke arrived but when I unpacked it, I immediately noticed that it was black in colour and shaped differently to the original. However, I put that down to an updated design and went ahead with the installation.

Unfortunately, the picture was only slightly better. The horizontal fold-over was gone but the lack of width remained, though the east-west pincushion and trapezoid were OK.

Anyway, I decided to check these circuits out.

First, I noticed that R1675 6.8W 3W was getting very hot and had partially melted the polyester capacitor next to it (C1670, 4.7mF 100V). I checked the values of these components but they were still spot on. I also checked Q1671 (2SD1830), L1670 (0.36mH) and diodes D1610, D1632 and D1633 and these were also OK.

Reluctantly, I came to the conclusion that I had been sent the wrong deflection yoke – particularly as the new one had additional coils fitted. As a result, I checked with my supplier and confirmed that RC1LH1879CEZZ was the correct part number. I then left a message outlining the problem with the Technical Support Officer for Sharp Corporation and he responded with a message for me to read Service Bulletin CTV182.

This bulletin told me that there are two types of CRT fitted to this set, the other being the VB68QBC230X3E. The yoke I had been supplied with was for this CRT only and, what’s more, the other one is no longer available.

And so all my hard work had been for nothing! The set has now been written off now as a new CRT is currently over $1100 trade. Fortunately, I did get a refund on the new deflection yoke.

A dead Yamaha

A dead 2004 Yamaha AV Receiver and 5 x 100W Surround Amplifier (RX-V750 [A] ) was recently brought into the workshop. This is a pretty expensive top-line home-theatre amplifier and uses some up-to-the-minute technology.

The reason it was dead was because the relay which switches the AC line to the main power transformer wasn’t latching. There was, however, +12V and + 5V (derived from the sub-supply) from IC501 to microprocessor IC502 (CPU MC30622MHP-161FP) but no output from pin 69 (PRY) to the relay (RY401).

I was subsequently advised that the microprocessor can give trouble in this unit, which filled me with dread as it is an expensive 100-pin surface-mounted chip. However, as luck would have it, an identical unit came in with a straightforward fuse problem. Having a twin meant that I could swap boards and I was able to replace the FUNCTION (2) board which carries the microprocessor. This made no difference, which saved everyone a small fortune.

I then went on to examine the RESET line in pin 12. I noticed that there appeared to be a hum on this line and it was unstable and down to 2.5V instead of 5V. I followed this line to the SUB TRANS board and began noticing quite a lot of inconsistencies between this unit and the good amplifier, particularly with regard to irregular waveforms.

The SUB TRANS power board is relatively small but still has quite a few components on it. Swapping this board with the good amplifier quickly confirmed that it was indeed the cause of the problem, so I immediately set about testing and replacing some of the more critical parts. I got nowhere until I came to FET Q404 (2SK3850). Although this measured differently from its twin, it didn’t actually measure completely faulty. However, after swapping it, I at last got the amplifier to power up on its own, so it must have been crook.

Unfortunately though, that wasn’t the end of the matter. Much to my frustration, the amplifier was still closing down intermittently and the RESET line and other waveforms were still incorrect.

I subsequently swapped quite a few more parts over without result before turning in desperation to someone who was an expert on this series of amplifiers. Apparently this board has been known to occasionally give strife and the fault is thought to be caused by a diode intermittently breaking down. As the module is only $35 retail, it’s simply easier (and more cost effective) to replace it, so that’s what I ended up doing.

The new module has also apparently been improved and carries several minor modifications. Anyway, it did the trick.

It comes in threes

I was asked to do a service call on a Teac CT-F683 TV set that was dead. When I arrived and knocked on the door, I was greeted by a man with a very sad expression. And was he having a run of bad luck. "Two weeks ago, my wife died. Last week, my dog died and now my @#$%& TV is dead", he told me. I immediately mouthed off some suitable platitudes and refrained from making my standard "bad luck runs in threes" quip.

This 68cm silver TV looks more modern than it actually is. In fact, the circuitry is quite conventional and has been around for a long time.

Fortunately, the power supply is on a sub-board at the rear of the set and Teac in their wisdom have used an inordinate number of screws to hold it down. Once you have spent the appropriate time removing these screws, the access isn’t too bad, as the leads are quite long. It also helps to remove the AV panel at the rear.

My initial checks showed that 240V AC was arriving at the board, which meant that the switch and fuses were OK. Other than that, there was no activity at all and the relay (RLY902) wasn’t latching.

There were no dry joints and nothing was burnt out that I could see. However, having serviced a couple of these sets before, I went straight for two resistors – R970 & R971 (15kW 2W) – which are in the lefthand corner and which looked discoloured. These supply the voltage directly to the relay coil. They measured OK but I replaced them anyway, to ensure long-term reliability.

The relay circuit is slightly unusual as it is not there to switch the set on and off. Instead, it acts as a safety cut-out if too much current is drawn by the low-voltage power supply involving transformer T970 and diode D976. This current is monitored by IC970 (TEA1501), which then controls Q971 and Q970.

Earlier Teacs used a very similar power supply, without this safety circuit and it was very reliable. In fact, it is ironic that it is the additional safety circuit that now gives all the trouble.

Resisting the temptation to just disable it, I decided to replace the four small electrolytics on the board – ie, C971, C972, C975 & C976. And when I removed C976 (1mF 250V), it was obvious that this was the culprit as it was leaking fluid down one leg. C972 (4.7mF 160V) wasn’t much better.

That was enough to repair this circuit and the set now came on perfectly. However, I also replaced C910 & C908 for good measure.

Unfortunately, there’s nothing I can do for the customer’s wife and dog.

Hospital TVs

I am occasionally called out to repair TV sets for a local hospital. These are modified Teac CT-M342HW sets and almost all of their problems can be sheeted back to capacitors C908 (47mF 63V) and C909 (10mF 100V) which are located next to heatsinks and, as a result, dry out rapidly with the heat. This problem, combined with power surges in the hospital, causes havoc with the rest of the set.

Fortunately, the faults are on the whole straightforward and are caused by excessive voltage being applied to sensitive circuits. I do have three odd faults with these sets though. One is intermittent weird patterning and streaking of the picture. This is due to the difficulty of trying to put the back on and lining up the chassis with the rails on the back shell of the cabinet. These rails tend to hit two 0.22mF capacitors (C303 and C304) on the edge of the board next to the tuner, making them dry jointed.

These two capacitors are part of the 0-33V tuning voltage circuit for the tuner. Re-siting and resoldering them fixes this problem.

The second problem I have had was switching the set on and off using the microprocessor. The power standby is controlled from pin 7 and this signal goes to Q601, Q905, Q906 and, finally, Q907 which switches the main +110V. During the normal course of repairs, Q907 (2SC2335) can go short-circuit and sometimes takes out Q906 (2SA1013). However, there is a 100kW resistor (R921) between Q907’s base and the collector of Q905 and two series reversed diodes (D913 & D914, S5295C) Q907’s emitter to the base of Q905.

As a result, I have never had Q905 (2SC2230A) actually fail on me. However, I have had many cases where it refuses to switch on with 0.6V between its base and emitter. In the end, I found that the only permanent solution is to replace it with a 2SC2335.

Lastly, I had one interesting fault with one set, where the complaint was lack of height. This problem could be overcome by going into the service menu on the RC-747 remote control (there are two little holes on top of the remote to access the menu) and adjusting it (normally, HIT is set for approximately 14-17).

However, this wasn’t really the correct solution and after poring over the vertical timebase, checking this and replacing that, I came to the conclusion that it was due to the 110V B+ rail being too high (it actually measured 130V). I adjusted VR901 and noticed the B+ rail swing down from 130V to 90V with only a very small movement of the wiper.

As there was some of that dreadful "snot" glue on it, I replaced the pot but it was still far too sensitive – in fact, it was impossible to set the voltage on exactly +110V. No matter how hard I tried, it was always too high or too low, with the picture height varying accordingly.

Well, I must admit that this had me perplexed. I spent a lot of time checking out the control circuitry, especially the three reference zener diodes. Enlightenment only came when I measured the B+ to be much higher and varying on the cathode of diode D911 following the chopper transformer. The cause was of this was a leaky 100mF 160V electrolytic capacitor (C917) at the junction of D911’s cathode and Q907’s collector and replacing it solved all the problems.

Don’t forget the CRT

With people so keen to purchase the new LCD monitors, it’s easy to forget that the old CRT monitor is still an excellent alternative – the more so because competition has forced their prices down to unbelievable levels.

I had two beautiful 21-inch 2000 Panasonic PanaSync S110i computer monitors (TX-DIF64MA 21HV125) come in which were either intermittently turning off or sometimes failing to start. They had been bought secondhand for a song (about one tenth of their value) only two years ago and had performed flawlessly. Now that they were faulty, and because we were starting from such a low value, the repair had to be equally cheap or it was computer heaven for these two.

At switch on, both were trying to come on but were then closing down due to some sort of protection circuit. On one, if I continually switched it off and on, you could eventually just see a white line across the screen. And that was the clue I was looking for.

Panasonic, being a premium brand, generally make an excellent product but even so, if the problem couldn’t be fixed within an hour, it was going to be curtains. Well, most of that time was spent removing and replacing the chassis from its impregnable metal cage. I removed a bucket or two of screws before the chassis was even half accessible. And once it was completely out, there was going to be no way to run these sets, so the fault had to either be visible or measurable with an ohmmeter.

Fortunately, in both cases, I could see that the vertical output IC (IC491) had a row of very fine dry joints and all I had to do was resolder them. A millennium later I had the sets all back together, ready for the final tests. Both monitors performed faultlessly – if only they were all that easy.

Grundig install

Recently, I was asked to do an installation and checkup on a complete Grundig system comprising a TV set, video, DVD, and digital set top box (DSTB)

When I arrived, the first thing I noticed was that it had already been installed by a dealer using phono leads and SCART adapters and also that the camera/game input at the front of the TV had been used. However, to get the most out of SCART systems, you need to use a fully-wired 21-pin lead.

These aren’t easy to get hold of because the catalogs and packages never tell you whether they are fully wired. The only way you can tell is to remove the plug covers and check yourself. If they aren’t, finding another supplier is another matter altogether.

The next drama was to find out which sockets to plug the leads into. Most of my client’s instruction books were missing and the ones he did have had very little information. However, most of the information is actually in the TV set’s "Easy Dialog" self-help menu system.

I connected the DVD output lead into the orange SCART socket (AV2) and the VCR to the black AV1 socket. The DSTB went to the blue AV2 socket (DEC/EXT) on the VCR. All AV connectors were set to RGB.

My client had complained of the recording quality on his VCR and I soon discovered this was because he was recording poor-quality analog signals and not the standard definition signals from the DSTB. The reason for this was quite simple – the latter was dead so arrangements had to be made to take it back to the authorised service centre.

I then decided to check out the DVD player, using a DVD which I grabbed from a pile next to the TV. This didn’t go smoothly either because, every few seconds, the picture rolled and the colour dropped out. This also happened with the drop-down menus and the DVD screen saver.

I eventually discovered that by swapping the VCR and DVD leads at the back of the TV, I could get good pictures on both inputs. This surprised me but apart from the TV OSD menu saying it was on VCR instead of DVD and vice versa, everything else was working properly.

I left the client to organise the repair of the DSTB and made arrangements to return when it was done. In the meantime, I contacted several people in the Grundig support system and I also trawled the web to try get to the bottom of this odd rolling on DVD. No-one within the company knew what was causing the problem off-hand but they said they would try to track it down and get back to me.

When the DSTB arrived back with a software upgrade, I reconnected it and left, telling the customer that I was still chasing the information on the other problem. However, days turned into weeks and to make matters worse, the VCR was "playing up" again.

I called back once more and found that the DSTB had failed again. This time, I suggested that when he took it back, he should also take the DVD player and VCR and have them checked.

The service centre repaired the DSTB again but no faults were found with anything else. Eventually Steve from "Electronics Today" came out and solved the problem.

There was in fact nothing really wrong – except me. Everything was plugged in correctly but when I had reached over and picked up the first DVD from the client’s collection, I had actually chosen an NTSC 60Hz Region Zone 1 disc! And the reason it played back on the AV1 (VCR) input was because that input was presumably configured for AUTO system while AV2 was configured only for PAL.

All that was required was to play a PAL 50Hz Region Zone 4 disc in the DVD player and it would have worked. I haven’t been back since, so I don’t know whether or not Steve reconfigured AV2 for AUTO (assuming it can be reconfigured).

So how did Steve know what the problem was? Well, he has been working on Grundigs for a long time and there’s no substitute for experience. Still, I should have twigged – it’s amazing what you overlook sometimes.

Finally, there is an extra button on the TV remote Telepilot 110C called the MODE function and we couldn’t work out how this let this remote control work the VCR or the DVD player as well. Steve let us in on the secret. This function only activates the buttons for the other equipment while the LED is on, which is for about 10 seconds.

Devilish cunning, those Germans – it makes you wonder how they lost the war!