Mrs Roseberry wanted a technician to call out and fix her 2000 Panasonic TC-68PS10 (MX8A chassis) because it had a white line across the screen and no picture. Obviously, the vertical timebase had failed and I was hoping it was just R519, the 1Ω feed resistor for the 28V rail that supplies IC451 (LA78045) and which is sometimes dry-jointed.

Well, I was right about this and it was quickly fixed, even though access to the board is rather difficult. Unfortunately, this revealed a second problem – the screen was now fully scanned but the bottom had foldover and the top was stretched. I did manage to check all the voltages on the seven IC pins (with difficulty because of the annoying plastic support bar that crosses this IC underneath) but they were all within tolerance of the voltages specified in the MX8 service manual.

In the end, there was nothing I could do but transport this heavy flat-screen set back to the workshop. Once there, I removed the plastic support and began checking everything out, first with an ohmmeter and then with the CRO.

The only waveform that looked slightly out was the output from pin 5 of IC451 where the ramp ended abruptly and flattened out. All the other waveforms looked OK. I replaced the IC and all the electrolytic capacitors around it one by one but nothing was making any difference.

Next, I connected the chassis to another set’s yoke (and vice versa) and this showed that the deflection yoke was OK. I then checked the 50/60Hz switching transistor (Q465) which was also OK and even swapped EEPROM IC1102 in case the software geometry controls were scrambled. Again, I drew a blank.

Grasping at straws, I next did the modification for resistor R404 (it was 9.53kΩ and is now 13kΩ to fix top lefthand line tearing). That done, I checked all the resistors on the top of the board and the surface-mounted ones underneath. I then tried heating and freezing the board, as well as vibration and twisting, but nothing was giving up any clues.

Items Covered This Month Panasonic TC-68PS10 TV set (MX8A chassis) Sony FD Series Trinitron KV-32FX65E TV set (AE-5 chassis SCC-Q14K-A) Panasonic TC-21PM50A TV set (GP3 chassis) JVC AV-28STEKGR TV set (JK chassis) Grundig Xentia 72 Flat MF 72-490/8 Dolby (CUC1832 chassis) Grundig Elegance 82 Flat MFW-82-3110 MV/Dolby (CUC 1935 chassis) Sony KV-ES29M31/SAU3 TV set (AG3 chassis SCC-P92A-A) Naim CD3 compact disc player

Basically, what I had was a vertical output IC with all the correct voltages and the correct waveforms going into it but with one distorted waveform coming out. I checked and tried disconnecting the feedback loops but this one really it had me stumped. And on top of that, Mrs Roseberry was hassling me for a quote and ETA.

It was time for some lateral thinking. Even though I had a perfect waveform going into pin 1 of IC451, I next turned my attention to IC401 (AN54415-E1), which is a 28-pin surface-mounted timebase control IC. I checked the 5V and 12V rails to pins 4, 15 & 25 and checked to ensure there was no significant ripple on these rails. I even replaced this IC (the electrolytics had already been changed) but it still made no difference.

So what else could I possibly do? The check service menus provided no clue and all worked as they were supposed to. It really was time to think outside the square and perform some unorthodox tests.

After first making sure there were no high-voltage rails nearby, I ran my fingers all over the vertical timebase circuitry with the set on to see if there was any effect. Well, the leakage due to my fingers gave a variety of distortion effects but nothing really significant until I got near pins 22-28 of IC401.

By wetting my fingers slightly and rubbing them across these pins, I could almost correct the fault. However, because the IC was so small (and my fingers are relatively large), I couldn’t initially identify which pins were the ones I was affecting.

A glance at the circuit showed that pins 27 & 28 are ground, while pin 25 is the +12V supply. Pins 26, 24 & 23 are marked "V SAW", "V AGC" and "V RAMP", respectively. I checked the voltage on pin 26 and it was correct at 4.85V. Pin 23 was also correct at +1.22V but when I checked pin 24, it read +5.5V instead of +7.16V – a difference of 1.66V!

Obviously, when I placed my finger on these pins, pin 25 (+12V) was able to pull pin 24 high enough to substantially correct the distortion.

The only component on pin 24 was C409, a 1μF 50V polyester capacitor (Part No: ECQV1H105JM3), so I removed it and checked it on my meter. There was no leakage and the value was remarkably accurate.

Despite this, I replaced it anyway and, as they say in the movies, that was that. The picture was now perfect, I was happy and, eventually, so was Mrs Roseberry. But what a rotten fault – little wonder I needed a stiff drink afterwards!

Transported from Spain

Mr Julio Sanchez had brought his 2000 Sony FD Series Trinitron KV-32FX65E TV set (AE-5 chassis SCC-Q14K-A) all the way from Spain. It was a multi-system TV, so he had no problem installing it here in Australia. However, it must have been fairly expensive to import, this being an 82cm widescreen set weighing 64kg.

Everything had been fine for Julio, except that he lived near the beaches and wasn’t aware of the risks involved for his beloved telly. When his set died, he really wanted us to call but I told him that the AE-5 chassis was not a common Australian model and that it would be better if he brought it into my workshop (the closest Australian model is a KV-EH36M31 using an AE5A SCC-U61A-A chassis).

Reluctantly, he finally arranged for it to be delivered and when I switched it on, the only thing I got was the front red LED flashing four times. This normally denotes a vertical protection fault, which could be due to R6835 or R6834 (0.47Ω) which supply the ±15V rails respectively, or perhaps IC6700 (STV9379) on the D Board going short circuit. However, I considered these possibilities unlikely in this case, as I couldn’t see any sign of the EHT starting (which is where these voltages are derived).

I started making measurements and found that there was +135V from D6617 but none on the collector of horizontal output transistor Q6804 (2SC5480-01). This was because R6895 and R6896 (0.47Ω) were open circuit, while Q6815 was short circuit. When replacing Q6804, I also found that C6815, a tuning capacitor, was invisibly dry jointed – ie, it looked soldered but the pigtail had not been properly inserted into its hole and was just resting on the entrance (incidentally, Q6804 can also be a 2SC5696).

This restored everything and the set was then soak tested to make sure there wasn’t anything nasty lurking about (such as the flyback transformer intermittently arcing).

The warranty job

We had a rather involved repair on a 2004 Panasonic TC-21PM50A TV set employing a GP3 chassis. It arrived in the workshop with the fault label saying it was "dead" but no-one had thought to ask how (or when) the problem had occurred – eg, was it the result of a thunderstorm?

The set was still under warranty, so I decided to tackle it the same day. When I opened it up, I immediately saw that resistor R801 (2.2Ω) which acts as a surge limiter to the bridge rectifier had blown open. In addition, the chopper (IC801) had been destroyed, along with 82V zener diode D820.

But that wasn’t the end of it and I soon discovered that optocoupler D860 and the IC802 (SE140) had also been damaged. And as I progressed through the set, more and more major damage was discovered, particularly along the 12V rail which had received a full 140V when Q850 (and R850) went short circuit. This not only took out several electrolytic capacitors (including C862, C880 and C2380) but also IC851 (a switching IC regulator supplying 5V and 8V) and also almost every other semiconductor along this rail.

At this stage, after consulting a Panasonic Technical Officer, it was decided that the chassis was a write-off – it would be just too expensive and time consuming to fix. And so a new one was ordered and fitted to the set.

However, I wasn’t out of the woods yet. The width was now too large (ie, it was overscanning) and there was no sound or picture – only a raster! Fortunately, this no-sound, no-picture problem was easily solved. One of the ceramic filter’s legs was shorting to ground because the solder pigtails hadn’t been cut short and had subsequently bent.

An attempt to fix the overscanning problem was initially made by entering the Service Menu Self Check Mode 3 – ie, by setting the off-timer to 30 and simultaneously pressing RECALL on the Remote and Channel Up on the TV front panel, then selecting CHK3 by pressing 2 on the remote. When EW-WIDTH was subsequently selected by button 4, the OSD (on-screen display) showed that was changed using the Volume "+" and "–" controls. In this case, however, the picture scan width didn’t change.

Comparing the two chasses, we could see differences in the flyback transformer, so I swapped them just in case. It made no difference!

Finally, the penny began to drop. This chassis model didn’t have any East-West correction circuits fitted and when the correct circuit diagram was examined, a link plug and socket (TPA23, 24 & 25) which switches in various capacitors in the horizontal deflection circuit was discovered. This link was missing on the new chassis and fitting a link from the old one over the appropriate test point reduced the width to an acceptable level.

The widescreen JVC

Frank Small was a round jovial character and I liked him even more when he brought his set in himself, rather than demand a service call. This was no mean feat, as the set was one of those heavy flat widescreen jobs – in this case, a 2001 JVC AV-28STEKGR using a JK chassis.

Its problem was that it would try to come on but it just couldn’t make it. The only sign of life was the rush of the EHT static just before it cut out. Obviously, the protection circuits were closing the set down but was it a faulty protection circuit or a real fault that was triggering them?

The service manual showed that pin 28 of microprocessor IC701 was the protect control pin and that in the normal state, it should be held high at +4.8V via R767. However, in Frank’s set, this pin was at zero volts. Desoldering it allowed the set to fire up and give a normal picture and sound, so what was causing the problem?

The protect line branches out all over the set and is in turn connected to the four power supply outputs via zener diodes, to the flyback transformer protection transistor (Q592) and to the x-ray protection transistor Q593. Each of these lines had to be investigated in turn.

I made a lucky guess by starting with the x-ray protection transistor. When I shorted its base to its emitter, the collector voltage immediately rose rise to 4.8V so I was on the right track. This transistor was being biased on by voltage from D593, R595 and D594, which in turn is fed by R524 from pin 8(AFC) of the flyback transformer T551.

I dusted down the oscilloscope and checked the waveforms of the line pulses on six pins of the flyback transformer and compared them with the service manual. Interestingly, all the waveforms were 10V higher than published (ie, 70V peak-to-peak instead of 60V). I then measured the main HT rail (B1) as +145V, which was spot on.

The size of the line pulses is determined by the values of the capacitors in parallel with the line output transistor (Q521, 2SD2553-LB), so these were the next to be checked. I started with C521 (2.8nF, 1.5kV), which I removed and measured with a capacitance meter. It read just 0.2nF or 200pF which meant it was almost completely open circuit!

Replacing it restored the correct waveform sizes and switched off the protection circuit. Frank was a happy man – even after paying my rather modest bill.

A couple of Grundigs

It seems that now Grundig is no longer a German company, I am called on to repair more of them – even though Grundig Australia is still apparently flourishing and supporting their products with excellent after-sales service and technical support.

I had a couple of examples turn up recently, the first being a 1999 Grundig Xentia 72 Flat MF 72-490/8 Dolby set (CUC1832 chassis). Due to their complexity, these sets do not lend themselves to being fixed in the home and I was grateful that its owner delivered it to the workshop. The complaint was that the picture was "half and half" – it was intermittently breaking up, was fuzzy, couldn’t hold its tuning and there was a "colour chromatic bullseye" effect.

Well, with these descriptive faults, I couldn’t wait to see the effects for myself. However, when I switched the set on, it was intermittently unstable, particularly in the horizontal axis, and the picture locked in with the sync bar down the centre. But what was more alarming was a burning smell and the noise of something arcing.

I switched the set off immediately and took a look at the main PC board. I soon identified the culprit as C53012, a 142pF 2kV capacitor on the collector of the line output transistor (T53001). This capacitor feeds 100V line pulses to the L1 line and these become the AFC reference pulses that are fed to the Feature Box Module (pin 28) and onto pin 26 of CIC 1410 SDA9362 S-DDC.

I replaced this capacitor and fixed the burnt hole in the PC board the original dry joint had created. This fixed the fault before I had a chance to see all the interesting symptoms described by the set’s owner but at least it prevented further possible damage to other parts.

The second Grundig set was a 2000 Elegance 82 Flat MFW-82-3110 MV/Dolby unit (CUC 1935 chassis). Unfortunately for me, its owner, Mr Trump, requested a service call – a not unreasonable request in view of the fact that this is 76cm widescreen set was located on the second floor of a block of units.

The set was "dead", although the multi-coloured LED did manage to change from red to amber when I attempted to fire it up with remote control (Tele Pilot 110C). I couldn’t see anything obvious initially and because access was so poor in the confined space, I eventually decided it would be better to remove the chassis and take it back to my to workshop.

Once on the bench, I soon found that the line output transistor (T53501, 2SC5331) had gone short circuit. In addition, R55514 (a 4.7W 2W fusible resistor) had gone open circuit, while pin 5 of IC55510 (TDA8145), the east-west correction amplifier, had gone short circuit to ground (pin 4).

Replacing these parts was somewhat difficult due to their location in the chassis and because of this, I fitted an IC socket – just in case. However, the job was eventually done with just a little fiddling.

Now the trouble with running a chassis on the bench without the deflection yoke is that there can be some unexpected consequences, due to the tuned circuit no longer being tuned and the tolerances of the components involved. To start with, I had to short out pins J3 and J4 of the deflection yoke plug in order to apply +A (142V) to the line output stage. I then shorted the base and emitter of T53501 together with a crocodile clip lead and hung a 60W globe off the collector to ground.

Overwhelmed by inactivity

When I switched it on, I was overwhelmed by inactivity. Nothing happened and I was getting no voltages out of any of the 13 secondary voltage rails. The only activity I had was the LED which still didn’t go beyond amber.

I had already checked the eight fuses fitted to the chassis and had confirmed there were no shorts on any of these rails. And so, having no prior experience with this model, I decided to ask Grundig Technical Support for a bit of a hand.

When I got through, I was obligingly told that I had to override the protection circuits (since the chassis was out of the set). To do that, you have to desolder pin 2 of the centre optocoupler (OK60546) or disconnect the base of CT61585 by desoldering link BR199. I asked about running the chassis without the deflection yoke but the Grundig technician didn’t know that I had linked pins J3 and J4 and therefore said it would be OK (my mistake for not telling him).

Well, the voltages did come up but the line output transistor blew again and the same resistor and IC also failed, plus a 315mA fuse (SI52501) to the line driver stage, for good measure. However, with no 142V being applied to the line output stage, all the voltages came up correctly.

I went to a lot of trouble to try and find out what "U COPY MODE" meant or was supposed to do and how it was tied up with "U STANDBY" and the "CIC21660 74LV00 quad AND gate". However, in the end, I only succeeded in confusing myself.

Next, I removed and checked all 11 tuning capacitors in the line output stage. I also removed the flyback transformer and tested it with an HR Diemen simulator but could find nothing wrong with any of these parts.

Finally, I decided the only option I had left was to bring the rest of the TV back to the workshop, despite all the logistics that involved. Ironically, after connecting the chassis back to the picture tube and yoke, the set fired up perfectly. There were no signs of stress anywhere, the voltages were all correct and the LED turned green.

Lots of static

The only niggly thing I noticed was that there was an awful lot of static between the picture tube and the plastic cabinet every time you switched the set on or off.

I phoned Grundig Technical Support once again and this time was put right as to what I had previously done wrong. And the technician confirmed that there is only one earth lead from the CRT aquadag to the chassis, via the picture tube socket. We both agreed that it could be salt deposits from onshore sea breezes that were causing the static problem and I was advised to either clean or replace the flyback transformer, which might have caused the initial problem.

In the end, I cleaned the picture tube glass and the cabinet, as well as the transformer and anywhere else I thought might be a problem, until the visible arc from the static rush disappeared. That done, I accessed the service mode (by using code 8500) but could find no error codes. I left it at that – there was no point pursuing software options as I had the set working satisfactorily. In short, it was best to let sleeping dogs lie.

After soak testing, the set was returned to Mr Trump with a warning to keep it dry and to cover it when he wasn’t watching it, to keep the salt-laden air off the circuit boards.

Ailing Naim CD player

We had a Naim CD3 compact disc player in for repair recently. This is basically an upmarket version of the popular Philips/Marantz CD56 series.

These can occasionally suffer from intermittent distorted sound and this is normally due to IC6305 – the DAC (digital-to-analog converter) – becoming temperature sensitive (too hot or too cold). Alternately freezing and heating this component will soon reveal whether or not that’s the problem, as it seemed to be in this case.

A new one was fitted (well, actually we fitted the Philips TDA1541P which costs just $15) but it didn’t fix the fault. This DAC is supplied by +5V, -5V and -15V rails, all of which were correct. However, the CRO revealed that there was substantial ripple on the -5V rail (V_DD2 on pin 26), caused by the failure of capacitor C2344 (47μF).

When freezing the IC, the capacitor must have been hit too, causing a change in the symptoms.

Anyway, we replaced capacitors C2344 and C2325 and reinstalled the original (more expensive) DAC chip. A soak test of the unit then showed that all was now OK.

Vacuum cleaner

Finally, I enclose a photograph of a common household appliance. As you can see, it looks pretty sophisticated with all those ICs. But what is it for?

Answer: believe it or not it is the control board out of an ordinary LG vacuum cleaner! Furthermore, it is cheaper to replace the board than fix it.

Where will it all end?