Both computers were brought in by Mr Galvin. The first was a slightly ancient 1996 Presario 4704 computer (series PSB220C/3590 Pentium) that was dead. The second was a 1998 Armada 1573D series 2920D notebook, which looked as though it had a faulty hard disk.

I started with the Presario PC, which had a faulty power supply. Unfortunately, being a Compaq, a generic power supply could not be fitted and exchange units were not really a viable economic proposition. The only option was to try to repair the existing one. I removed and disassembled it on the workshop bench.

When it was finally in pieces, the major clue to its demise was plainly visible, namely a large female cockroach, complete with egg sac, which had managed to electrocute itself on the track side of the board. Removing the corpse and cleaning up its corrosion was probably all that was needed (the mains fuse hadn’t blown) but I also replaced all three of the small electros (1μF to 4.7μF) on the supply plugs. I also checked the high-value resistors.

I didn’t want to refit the supply to the computer only to find it was still faulty, so I fitted a 12V 36W car globe to the 5V rail as a dummy load and turned on the power. The fan started and the globe lit. Satisfied that all was OK, I then refitted the unit and found that the machine was now working normally. So one set down and one to go.

I now turned my attention to the Armada 2920D notebook which was fitted with an Intel Pentium 233MMX microprocessor. Its problem was that it wouldn’t boot up. Instead, it was displaying a "1720 Intelli-Safe Hard Drive Detects Imminent Failure" error message, followed by a "Non-System Disk or Disk Error" message.

Items Covered This Month Compaq Presario 4704 computer. Compaq Armada 1573D notebook. Panasonic TC29V26A TV set. Grundig ST70-75S TV set. Philips 33FL1880/75R Matchline TV set. AWA SC6341 (AS630) TV set. Panasonic TC-29V50A MX-2A TV set.

The next problem was that the computer belonged to Mr Galvin’s son. This probably accounted for its failure and also for the complete loss of instruction books and utility disks. However, all was not lost and a few hours on the Compaq web site produced a nearly complete set.

One of the utilities I downloaded is a diagnostics program (PC Diagnostics). This reported no diagnostic partition and a password protected hard disk lock. The latter proved not to be the case. A more precise message was, "1799-08 failed cable test and buffer compare".

I then ran Fdisk and this said that there was no partition. However, it wouldn’t save the instructions when I tried to create a new partition. Norton Diagnostics found no problem but Disk Doctor found "Invalid Signature in Partition Table" and "Bootable Partition cannot be booted from".

All the above seemed to indicate a faulty hard disk but to confirm this, I contacted Compaq Technical Support who also thought it was a hard disk problem. However, I decided to take one more precaution – I took the notebook to a local computer specialist and ask him to fix it. He also diagnosed a faulty hard drive and quoted to replace the 3.2Gb IDE IBM hard drive with a 6.4Gb IBM Travelstream hard drive.

After getting the quote accepted by Mr Galvin, the new hard disk drive was ordered and duly fitted. But guess what – we still had the same error messages.

This meant that the fault had to be on the motherboard, most probably in the IDE controller section. Unfortunately, a new motherboard would cost over $1200 and I was beginning to feel that I was out of my depth.

After consulting Mr Galvin, we agreed to take it to one of their official agents and invest $50 in a quote. Not surprisingly, the official diagnosis was the system board but, fortunately, they offered a repaired/exchange board with a three-month warranty for only $550 fitted. We agreed on this and a few days later I picked up the repaired computer and reinstalled the original software. I tested it thoroughly but no more problems were found.

I subsequently quizzed the service department as to what had caused the problem but I drew a blank. Because it was an exchange unit, no one knew the answers – perhaps Mr Galvin’s son might.

Large TV sets

Now about those large TV sets – and they are getting larger. Though I try to look calm on the exterior, I always panic inside when I agree to repair a large TV set with what could be a nasty problem in the home. By and large it is much more sensible to take the set to the workshop rather than the workshop to the set.

However, the public perception seems to be that all faults are simple enough to be dealt with in the lounge room. After all, it can’t be very serious, they reason . . . the fuse, the on/off switch or a bad connection. And bad connections are easy to find; so easy that some customers consider they shouldn’t even have to pay for them!

It’s the same with VCRs. I had a case recently when an ancient VCR had come into the workshop because it was chewing tapes. It was duly fixed and the customer took it home. Hours later I received an irate call from the same individual who was furious that I had ruined his VCR and he wanted his money back. I tried to calm him down and work out what the problem was.

Very heatedly, he said that the set was dead and nothing worked. This was hard to believe, so I asked whether the clock was working. "Intermittently", was his response. Asked to explain this, he came back with "well, its on now, its off now, its on now, its off now".

It took 10 minutes of patient talking before he learnt how to switch the VCR on and set the clock . . . and he had only owned the unit for 10 years!

Panasonic TC29V26A

But back to the present. There were several large TV sets in the workshop but at least these were in a controllable environment (mine). The first off the rank was a Panasonic TC29V26A, an M16MV30 chassis. This 8-year old set had had a tough life, lived near the sea and was badly corroded.

The set came in dead, which turned out to be a faulty horizontal output transformer and horizontal output transistor. This was a straightforward routine type fault and the set was left on test afterwards.

When Mr Rose called to pick it up he asked whether I checked the tuning – implying that he had mentioned it when he had brought it in. Well, I didn’t recall that and I don’t think he did. But, anyway, I hadn’t – the set appeared to be working with most stations. It didn’t occur to me to check them all as I wasn’t aware of any problem.

Of course, when I tried it out in front of him, the problem confronted us. The automatic search certainly tuned in the stations but just wouldn’t stop and be memorised.

Considering the corrosion of the motherboard, it was a wonder the set was working at all. In addition to the usual 5V and 12V rails, the tuning system required a 30V rail. These were all available on the tuner/IF module B. The tuning voltage was derived from pin 46 of microprocessor IC1213 (MN1872432TW1) on the E board and applied to Q1202. This then varied the voltage applied to the tuning pin of the tuner.

The IF from the tuner goes through Q110, Q101 and Q105 to pins 20, 21 & 23 of IC101. The AFC output is at pin 12 and feeds the tuner, as well as the microprocessor (pin 10) via IC102 (pins 3 and 4) and Q102 (TP891). The microprocessor detects, controls and stores the data in the EEPROM (IC1211). The problem was where to start looking.

I reasoned that as the corrosion was worst around the microprocessor, I had only to check the tracks running to it and any small components around it. The prime suspect was diode D1203 from the AFC input (pin 10) to 12V. As it happened, this was a bullseye; substituting a new 1N4148 for the MA700 fixed the problem. From experience, I know that Panasonic small diodes do not like corrosion!

Dead Grundig

The next set was a dead Grundig ST70-75S using a CUC 6360 chassis. This, too, had a short circuit horizontal output transistor (BU508AG, T568.)

Whenever I see a horizontal output transistor that’s gone short circuit, the question is "why did it fail"? In this case, I felt sure that the horizontal output transformer was to blame even though it looked good. Most Grundig transformers have a clear plastic outer cover and when they fail they sometimes leave a dark colour or shade on the inside. Unfortunately, there were no such clues here.

The question was, should I risk simply fitting another transistor or should I also change the transformer at the same time? I decided on the latter course, as I didn’t want any recalls at a later stage.

I duly ordered and fitted replacements for both, only to be disappointed by the immediate failure of the new transistor (the manufacturers had substituted a 2SD1884). I thought I was into one of my usual messes when I noticed C511, a blue rectangular 9nF 1600V capacitor in the collector circuit of the horizontal output transistor (T568). This capacitor was no longer perfectly shaped but had a bulge in it. This value is not available off the shelf and its part number is 8515-911-695.

Its replacement turned out to be a green 9.5nF capacitor, which, I was assured, is now the default value for 66cm versions of this chassis. Replacing it finally fixed the fault but left the geometry needing a slight adjustment.

This is one of those irritating sets that cannot be serviced without its remote control. To get into the service mode, one has to press I, select special functions and dial 8500 to get into the service adjustments.

Also, supposedly, one needs the remote control to switch the set on because I was informed that an "S" connector on the motherboard had been disconnected.

However, I couldn’t find this and as the set was now working properly and the customer had money in his hands, I resisted the temptation to take it further.

This reminded me of a small AWA C3426 with a Daewoo chassis that was also dead. After spending a lot of time checking out the TV set, I found out it was the remote control that was the problem. The batteries had been left in too long and corroded the PC board tracks but only for the power on/off and volume functions. Linking the corroded tracks restored these two functions and let me switch the set on.

Big Phil

Next were two large Philips TV sets, one of which was a 33FL1880/75R Matchline using an FL1.1-S AA chassis. This 84cm set was a "top-of-the-range" unit about eight years ago but this one was nearly dead. All that was showing were the mute, stereo and power front panel displays and these were all pulsating.

The service manual refers to code 99, and there is a sort of fault-finding tree chart in Section 8. Following this, I put the set into the Service Default Mode by shorting S24 to S25 and found test point TP56 was at 4V ("set power on" should be 17.5V and "set power off" should be 0V). There was no 141V on TP57. I really wasn’t any the wiser for all this and suspected that I could diagnose this better by using commonsense rather than their error codes.

The set uses a SOPS or Self Oscillating Power Supply (the output voltage is controlled by the frequency). I noticed that TP60 measured 18V and I was getting a feeling that the problem wasn’t in the power supply but probably in the horizontal output stage. This 84cm set actually uses two output transistors in parallel and these are designated ON4673A (or BU508AF). One of them, Q7504, was a dead short.

Access to the underside of this set is really difficult and in the end I decided that the best course would be to unplug everything and pull it right out. Muggins also decided it wouldn’t be necessary to mark where each lead should go back, as logic and the service manual would easily sort this out. That was a BIG mistake.

After many hours, I still couldn’t work out where all the plugs went back – especially the 26V supply to the SCAVEM (Scan Velocity Modulation) board on the neck of the tube. It was only after Philips had very kindly sorted me out that I discovered that there is an error in the service manual. In fact, the lead is connected to 28V and the two leads plug onto IL62 and IL63.

They also told me that the main causes of failure of this transistor are due to C2504 and C2523, which are 8200pF and 470pF respectively. I replaced both of these, reconnected the board and switched on.

Everything now worked well except that it was stuck in the service mode, which gives a row of figures on the screen. The manual states that to exit this mode, you press the personal preference button on the front panel of the set. In reality, I found that this would only happen if I switched the set off using the remote control.

The second Philips set was a current model 34PT5793/79R A8.0A AA, still under warranty. Its problem was a bright uncontrollable white raster before the set cut out.

I measured the cathode voltages on the tube but found nothing. I could see that R3840, which supplies 200V to IC7830, was badly burnt. I then checked IC7830 to find that it was totally short circuit. The circuit diagram had it marked as a TDA6103 but the spare parts list had it as TDA6107Q; the same as was fitted in the set.

I ordered a new IC and fitted it along with a new 100Ω resistor, which was all that was needed to restore the picture. I suspect that the IC failure may have been due to a CRT flashover.

AWA stereo TV set

Mr Staples wanted a house call to his 15-year old AWA SC6341 (AS630) TV set. This is a large stereo console lowboy and his complaint was that the "sound was unclear". I don’t know how I was persuaded to attend such an old set but there I was in his dark and dingy sitting room with the set, plus his VCR and a book rack of cassettes on top, while Mr and Mrs Staples were having a meal and watching me.

The "sound unclear" was actually a distorted left channel. Access to the back of the set was appalling and access to the boards inside the set wasn’t much better. It would mean lying full length on the floor to work on it. I reasoned that, as it was only one channel, it was probably the sound output IC or preamplifier – I would order one and return later.

This was an overconfident assumption on my part because on the next visit, after I had replaced IC3A2 AN7158N and IC3P0 M515236, it still had the fault. Using an audio probe, I eventually traced the problem back to the TDA3800G stereo decoder (IC302).

Replacing this didn’t fix the fault either. It was then that I remembered fixing the same model some years ago for the same fault. In that case, the problem was that the three subminiature pots that are used to set up the stereo decoder were badly corroded. Replacing them is the easy part but aligning them in the home without the correct equipment (a stereo generator, etc) is just too difficult.

I offered the Staples a short-term partial solution – just turn the balance control to the right, which would mute the distorting left channel. This would have been fine except for the even more ancient National NV450 VCR connected to it. Being mono, the left and right channels were both muted. Not being a quitter, I suggested connecting the VCR via the AV leads and settle for dual-mono.

However, for some unknown reason, the audio output of the VCR was much lower than that required by the TV set and the result was still unsatisfactory – besides which, they had lost the VCR remote control and wouldn’t be able to change the channels while they ate their meals.

Mr Staples was clearly totally unimpressed with my efforts and claimed that I had made the set worse. I was finally shown the door and the last I heard was they bought a new TV set. I only wish that they had done this before calling me.

Another ancient set

Not to be outdone, fate determined that stupidity would rule the day. I accepted another call for another ancient set – a Mitsubishi 2SC6343 AS631 with lack of height, rolling when cold, and a white vertical bar on the lefthand side. I was, I was told, the first technician to attend this set in 15 years, which says a lot for Mitsubishi.

After spending an uncomfortable half-hour resoldering suspect joints, I concluded that the problems were probably due to dried out electrolytics on the motherboard and possibly in the power supply. Unfortunately, I didn’t have my ESR meter with me so I decided to measure all the supply rails in the set and compare them with the circuit.

Everything measured OK until I reached the 14V rail input to Q552, which was very low. Replacing C562 (100μF EXR 35) fixed all three symptoms at once, except for a touch of poor linearity and top retrace lines. This turned out to be a very sick C454 (10μF EXR 100) in the vertical output stage.

I really should stop repairing sets that are over 10 years old. They always lead to trouble.

Another house call

Another house call was initiated by a Mrs Hayes. She wanted me to fix her dead Panasonic TC-29V50A MX-2A TV set in her home. I was envisaging all sorts of major problems like horizontal output transformers or worse, blown switchmode power supplies. Some of the modern power supplies these days are fairly complicated and difficult to diagnose.

Fortunately, this circuit was reasonably straightforward and conventional, using an optocoupler feedback between the hot and cold sides of the chopper transformer to control the output and standby/on positions.

There was voltage on the primary side but only a little on the secondary side and the standby LED was off. Further checks showed that the cathode of D808 was at 15V but there was nothing on the emitter of Q802 due to R833 22Ω being open circuit.

At this point, I had a quick interlude for a prayer – please, please, let this be the only fault in the set. My prayers were answered; replacing the resistor restored all the functions on the set. Sometimes a faulty Q802 can be the cause of the resistor failing and sometimes the whole circuit can be destroyed. I was lucky this time.

Well, almost. The set was sitting on a very attractive stand with a companion Panasonic hifi VCR on lovely polished floorboards. When I had rotated the set to get access to the back, I had needed to lift the corner of a mat to allow the castors to roll past. And of course, I had to do the same when putting it back into its normal position.

Unfortunately, as I was putting it back, the castor caught the edge of the mat and required just a tiny, tiny shove to push it free. But when I did this, the whole stand suddenly collapsed like a deck of cards and the 50kg TV set landed right on top of me.

I was in shock – I thought an earthquake had occurred. I just couldn’t believe it; I hadn’t pushed the stand very hard and it had collapsed right on top of me. The noise was also deafening in the otherwise quiet house and it certainly attracted Mrs Hayes’ attention.

Fortunately there was no real damage; I had taken the weight of the TV set which was unmarked by the incident.

When I started to reassemble the stand, it quickly became obvious why it had collapsed. It is held together by plastic studs and some of these were missing while others had broken. The whole thing was just holding together. It was fine if left untouched but if pushed laterally, it all came tumbling down.

I was a little bruised and my ego was somewhat dented by the need to explain all this to the astonished Mrs Hayes. But really it wasn’t my fault – there was no way of telling how poorly the stand was constructed.

Anyway, I managed to get it all back together and it still worked properly. So maybe I was lucky after all.