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SERVICEMAN'S LOG Some sets go on forever There is always a small percentage of older sets being presented for service and they usually call for a special approach. Are they worth fixing? Are any hard-to-get components involved? How valuable is the set to the customer? In practice, each case has to be treated on its merits. This story concerns one of those old timers - a Rank Arena model C2053. This was one of several Rank models which appeared shortly after the introduction of colour TV in Australia. These included the C-2601, 02, 03, 04, 05 and 06 (all 63cm models), and a similar range of 51cm models starting at the C-2201. The set in question comes from a third range with the 20 prefix - 48cm (20in) - but the suffix 53 suggests that it is a later model than those listed above. However, there is some doubt about this and I am not sure exactly where it fits into the manufacturing sequence. Significantly, it has a VHF only front end. However, the point about mentioning these ranges is that all the sets from them are very similar. Many of the boards are used in all models, the main differences generally being confined to just one or two boards. Typically, this includes the output deflection board which is changed to suit different size picture tubes. Something old In this case, the set was almost the same as the 2601/2201 series, the most obvious difference being the "Deflection Out" board which is designated PWC-497 (PWC-315 in the 2201). The customer brought it in together with a Sharp video recorder which, in addition to its normal role, was being used with the Rank as a UHF downconverter. Both units needed attention but the video recorder was a fairly routine problem. The Rank TV set was not quite so straightforward. These early Rank sets must have set some kind of record for longevity; some owners have likened them to the old DC3 aircraft - they just seem to go on forever. One 2601 that I know of started life just after colour was introduced (in 1975), probably chalks up three hours or more a SON\~ OWN~'R'S 'r\A.\J6: day, and is still going L-\ Ke:.N E.t> 1l-lE.SE::'. S:.A"R\..-'( strong with plenty of RANK St;."'t'"S , D OL-D brightness and con-OC. 3 A\~Ct<.AF~, .. trast in the tube. 56 SILICON CHIP And that raises the question as to how long is it economical to keep any particular set going. Much depends on the condition of the tube. If it is in good nick, and the fault is unlikely to involve other specialised components, then repairs may well be justified. It is really up to the owner. On the other hand, the need for a new tube is another matter. Normally a reconditioned tube would be available and, for what it is, the price is very reasonable. But by the time fitting and other costs are added, the proposition begins to look a bit dubious. To justify it, one must assume that the set is going to run for several more years without developing any serious faults. Again it is up to the owner but, when I point out these factors, most decide to cut their losses and put the money towards a new set; one which will normally offer more features than the old one. And so the old set finishes up on the tip. But not before yours truly has picked it over. The various boards, in particular, are well worth salvaging, especially in view of their universal nature, as mentioned above. Something wrong And that brings us back to the set in question. A quick check suggested that it was well worth saving. It was working (almost) and the picture tube appeared to have plenty of life left in it. The main problem was that it had no vertical or horizontal sync. 1\viddling the vertical hold control brought this back into sync and with a good.normal locking range. No problem there. But the horizontal system was a different matter. I could lock it but it was extremely critical. Something was obviously very wrong. Nevertheless, I felt that the set was well worth saving and advised the customer accordingly. I was banking on the fact that the fault would almost certainly be in the "DefBoard", PWC- PWC - 367 DEF BOARD RS6C 6. 2 K I 1 RS':> 5 ~ - ~== ~.5'l. 1 ..''c,' fi~J.~ SL:' :;, _: R.:."~ 1$C~!lJ..~.L 0501 s~if~1M ~-~l; J;;: ◄ 7 l ; ii~R t~3~ ~~s~ ,.,.. -,. ~~i~ r ~~J ... 1n~:~ "-,~,:',::::~,·";::_l~.-c,-_s,,_: _-,;;-_-~.-':S !____ , f/;_'..:,_. ,. ~,, _,_. - - - - - - c""'-o~ 5=,- ' ... I ~•;~·/':/ _j "' SJ ; ':'CF - ,-. . f :>??. ,I I l 3.. 7 l- ~·! 1 ~:-:·f' i ~}--:c ., • ;i:' i l ; ~ -- f'-+ - I r!!io ,J, --'-'-0 ~~;;::'-_-·. ·-~;-_ ,:~_-~\-._ ______,I n. I 'f',_,,, ,I Il ' I ~-LJ 9:~-- - - - t.___. ,,. :- : ,, Fig.1: part of the horizontal deflection circuitry in the Rank Arena C-2053. The horizontal output transformer, T552, is at extreme right, the connection between PWC-497 and PWC-367 at centre, and diodes D501 & D502 at left. 367, which carries the vertical and horizontal oscillators, plus the sync circuitry. And, with the stock of spare boards I mentioned earlier, it should be a snack. In fact , this is a technique I have been using extensively on old sets like these. A board replacement is usually all that is needed, the old board can be tossed,, and there is no time wasted searching for elusive faults. Nothing to it! So it was out with the box of discarded boards which quickly yielded a PWC-367. I then tackled the fiddly job of unplugging the umpteen connectors on the suspect board, fitting the replacement board, and replacing the connectors. The only snag was that it didn't achieve anything; the fault was just as evident as before which was a bit of a blow. I had been so confident that the fault would be on this board that I hadn't considered any other possibilities. But now I had to. The next likely suspect was the Video IF board, PWC-312 , and the possibility that it was not delivering proper sync pulses. The video signal comes out of PWC-312 on connection B1, enters PWC-367 on B1, and goes to the sync separator (TR401). I took a look at this waveform on the CRO and, as far as I could judge, all was normal. But I was at something of a disadvantage here because the circuit diagram carried no waveforms - a common shortcoming of the Rank manuals. The closest data I had was from the 2201 manual; one of the few that did carry waveforms. In this case, the relevant waveform, from TP17, looked similar to the one I was viewing. However, the manual's reproduction wasn't particularly good and I couldn't be certain that there were no subtle differences. I decided that the easiest way to be sure was to make another board switch - except that when I delved into the box for a replacement PWC-312, there was none. So that brought the whole exercise to a halt for the moment. In any case, pressure of other work dictated that I put the set aside for the TETIA TV TIP Sony KV2764EC Symptom: the set had been cutting out but finally died altogether. The fault was on the 20V rail and turned out to be a shorted sound output chip IC252. Within a few days, the set was cutting out again and the serviceman attended to it in the owner's home. Cure: it turned out that the owner had connected two large external speakers to the set. The sound output chip wasn't intended to drive this sort of load and is fitted with a very small heatsink. Removing the speakers solved the problem, although a larger heatsink might have been an alternative. TETIA TV Tip is supplied by the Tasmanian branch of the Electronic Technician's Institute of Australia. Contact Jim Lawler, 16 Adina St, Geilston Bay, 7015. time being, which would also give me time to think. It was a couple of days later before I thought much about it again and then only because I was looking for something else in the storeroom. Among other things, this storeroom also houses scrapped sets and components and I realised that there was a complete Rank chassis waiting to be stripped. So there was the PWC-312 video IF board I needed. I fished it out, dusted it off and fitted it into the set. And that was the second setback; the fault w as still there, exactly as before. That meant that the time for short-cuts was over; I now had to get the brain _into gear and do some real troubleshooting. Something on my mind However, right now, there were more important jobs to be attended to and so, once again, the set was put to one side. But it was never too far out of mind; I once knew these sets inside out and it was shock to realise that time had erased this familiarity. If the fault wasn't on either of those two boards, where was it? I was obviously missing something but I couldn't figure out what. The set was apparently more on my mind than I realised. In the wee small hours one morning several days later, I awoke with a start and could visualise the circuit quite clearly. More than that, I knew where to look for the fault (the brain sure works in a mysterious way). Cursing myself for being all kinds of a stupid clot, I realised that the third board in this group, the "Def Out" board (PWC-497), had to be the culprit. Why? Because the discriminator section of the flywheel sync cirFEBRUARY 1992 57 SERVICEMAN'S LOG - CTD cuit- diodes D501 and D502 on PWC367 - needs a reference pulse from the horizontal output transformer before it can function. I could hardly wait to get to the bench that morning, fish out the circuit, crank the set up and delve into it w ith the CRO. But there was the major snag I mentioned earlier; the manual has no waveforms and very few voltages. The best I could do was fall back on the 2201 manual but this was of limited value in this case because the Deflection Out board for the set in question uses a different circuit arrangement. However, the 2201 manual was of some help. It shows the pulse line coming off pin 3 of the horizontal output transformer and designates this as waveform TP32. This shows sharp spikes, at horizontal frequency, with a value of 250Vpp. The 2053 shows the pulse line coming off pin 9 and the CRO indicated a virtually identical waveform. But 58 SILICON CHIP whereas the 2201 pulse line uses a passive arrangement, the 2053 adds a transistor (TR505) as an AFC amplifier. In both circuits, the pulse line leaves the Def Out Board and enters the Def Board via the H4 pins. The 2201 manual gives no waveforms along this line - which features various wave shaping comp£?nents - but it does show the waveform (TP26) at the junction of the discriminator diodes as a sawtooth pattern with a value of 4 Vpp. From this , I felt that it was safe to assume that a similar waveform would be required at this point in the 2053 . Well that was something, even ifI had no indication of what to expect at various points along the line. In fact, a check at H4 on the Def Out Board was most revealing. The best description of the waveform is that it was similar to that from a half-wave rectifier, consisting of a series of roughly sinusoidal pulses separated by spaces of approximately equal length, and with an amplitude of about 2Vpp. Well, even if I didn't know exactly what the waveform should be, I was fairly certain that it shouldn't look like that. And because there was no problem with PWC-367, the fault had to be on PWC-497. Something suspect My first suspects were two electrolytic capacitors in the pulse line: a lµF type, C558, ahead of the AFC amplifier transistor (TR505); and a 10µF type, C556, following it. Low value electrolytics are notorious for drying out and these were quite old. The lOµF capacitor was marginally easier to get at, so I lifted this first. It checked OK. Not surprisingly, lifting this capacitor completely killed what little horizontal sync there had been. I could float the picture but that was all. But the real surprise was that this also killed the vertical sync. I have no explanation for this. I have poured over the circuit trying to find a link - even an accidental one but without success. No doubt, given the time and the right facilities, the reason could be found but there is a practical limit to the time one can spend on such problems. Perhaps a reader has the answer, in which case I'd be happy to hear it. Getting back to the main problem, I next tried the lµF capacitor, feeling certain that it would be the culprit. Again I drew a blank. I also drew a blank with all the resistors in the chain, which left only one thing - the transistor. It tested perfectly but I've been caught that way before. The only real test is to replace it. I didn't have a 2SA539 on hand, so I substituted a BC556. And that was it - the system locked rock solid with a good wide locking range. Problem solved. And when I checked the waveform at H4, there was a sawtooth similar to the one shown at the discriminator diodes in the 2201. Its amplitude might have been a fraction less but, if anything, it was a better sawtooth than the one shown. But what was wrong with the transistor? It tested as having normal gain and there was no indication of leakage. I can only speculate that, for some reason, it had lost its high-frequency response . As a result, it could no longer handle the higher frequencies which make up a sawtooth waveform and reduced it to something like a sine wave. So that was the end of the exercise and the set went back to a very satisfied customer. However, one of the points arising out of the exercise is the difficulty of working without waveform and voltage information in service manuals . And I'm not just harping on about the Rank manuals; they are history. What I'm really concerned about is a similar trend in the latest manuals; a complete lack of waveform data and only limited voltage data. Samsung is one of the most serious offenders at present. So serious is this that I am looking for some convenient way of building up my own waveform references as sets pass through the workshop. Photography is one approach but it has serious practical limitations. For starters, this would require a suitable photographic jig attached to the CRO, to reduce the process to simply pressing the button. And there is a real need to record the test point details on the film, along with the waveform. Any other arrangement is prone to mistakes . A more recent approach is a system which can couple the CRO to a computer and, ultimately, reproduce the waveform via the computer's printer. I'm looking into this one. But it would be a lot easier if the makers did their job properly. FRACARRO SAVES... ... more than $10. from every UHF television antenna you buy. Fracarro's 4PUN for better performance from weak UHF signals. Peter C. Lacey Services Pty. Ltd. P.O. Box 678 (74Fulton Rd.) Mount Eliza 3930 Tel:03 787 2077 Fax:(03) 787 3460 ACN006893438 Something new For a change of theme, we now go from one of the oldest sets around to one of the latest. This is a 37cm colour TV set which I recently acquired for use as a workshop monitor. Apart from a minor technical problem, there are a number of interesting points about this set. It carries the Hitachi brand - or Hitachi Fujian Model HFC- AUSTRALIAN MADE TV TEST EQUIPMENT Happy New Year Specials. 10% discount on all test equipment. 15% discount on two or more items SHORTED TURNS TESTER Bu ilt-i n meter to check EHT transformers including sp lit diode type, yokes and drive transformers . $78.00 + $4.00 p&p 1425B to be precise - but it is not marketed by Hitachi. It is made in China and marketed in Australia through the China Trade and Exhibition Centre, 26-34 Dunning Avenue, Roseberry, NSW 2018. I have dealt with Chinese sets before in these notes and, not to put too ANTRI TOROIDAL TRANSFORMERS HIGH-VOLTAGE PROBE Built-i n meter reads positive or negative vo ltages from 0-50kV. For checking EHT and other HT vo ltages. $98.00 + $5.00 p&p DEGAUSSING WAND Strong magnetic fie ld. Double insulated for your safety with momentary switch operation . 240V AC 2.2 amps. As important as a soldering iron! $75.00 + $10.00 p&p REMOTE CONTROL TESTER Designed to test infrared or ultrason ic contro l un its. Supplied with extension infrared detector lead . Output is via a LED and piezo speaker. $84.00 + $4.00 p&p :s.. _, "S;'-- -.J\+~// t-~ ~~ -- TUNER REPAIRS -~ ~~~ From $19 exchange plus post & pack Cheque, Money Order, Visa, Bankcard or Mastercard .,;v! !,U~ERS} ~~~e~Jl~:i~.~~1d2, Phone (02) 774 1154 Fax (02) 774 1154 • • • • Now made in Australia Standard range 1SVA to 2kVA Large ex-stock quantities available Competitive pricing available for OE Ms & resellers • Simply the best transformers all round HARBUCH ELECTRONICS PTY LTD 90 George St, Hornsby, NSW 2077. Phone (02) 476 5854 Fax (02) 476 3231 FEBRUARY1992 59 spare parts backup? This a grey area at the moment. The set is sold with a 12-month replacement warranty; that is, if the set fails within 12 months, it is replaced with a new set. After that, it appears that you are on your own. This may not be too bad provided there is a guaranteed supply of major spares but I have not been able to get a clear ruling on this to date. Frankly, I consider that this point could make or break the commercial operation in Australia. SERVICEMAN'S LOG - CTD fine a point on it, I was not particularly impressed by the workmanship involved. So to be fair, I must say that this effort appears to be a better proposition. Time alone will tell, of course, but my first impression is of a very wellmade unit offering a large number of features at a very competitive price (around $350). Recently, I was interested in acquiring another VCR monitor for the workshop and so, when my dealer colleague put some on display, I had a closer look. In fact, he was happy to lend me one to evaluate, as much for his benefit as mine. I was particularly interested in the remote control features and on-screen displays, which are quite extensive. This can be very valuable in practice, as when soak-testing VCRs for intermittent faults. It also allows the monitor to be located in the best viewing position, regardless of accessibility. The remote facilities include: on/ off control; off-timer, selectable for 30, 60, 90, or 120 minutes; program Something wrong mode providing brightness, colour and volume control (with on-screen value bars); on-screen clock; and step-bystep channel selection or specific channel selection via a set of 12 pushbuttons. In the end, the features were impressive enough for me to clinch a deal with my colleague. But what about the warranty and Getting back to my own set, I soon discovered a problem with the onscreen clock, which seemed to work OK initially but, after about a day, appeared to be running fast. Sure enough, a more careful check revealed that it gained nearly five minutes over 24 hours. That puts it on a par with the old alarm clock that used to tick away on our kitchen mantlepiece when I was a kid but I expected something better from a crystal. The crystal in question (Z101) is the same crystal that serves the microprocessor and is connected between pins 28 & 29 of this IC. It is marked as Introducing the Protel advantage. Protet®for Windows':' Prate!for Windows is an entirely new Printed Circuit Board design system created for Windows 3 . Prate! for Windows brings the professionalism of Protel's proven PCB design software to the highly productive Windows 3 environment. New Prate! users will start designing sooner and experienced users will work more efficiently than ever. In 386 advanced mode, Windows 3 provides vi11ual memory capability, which allows advanced PCB users to design without restrictions on the total number of components, nets, tracks, etc. Prate! for Windows supports the multiple document interface (MDI) standard. Any number offiles can be loaded Special-------~ Copper Trace Layers □ Midl - □ Mid8 - □ Mid9 □ Mid 3 !ll □ MidlO l!ffll □ Mid 11 iZITop □ Mld4 - □ Mid12 □ Mid 5 OMid6 □ Mid 7 liifil □ Mid 13 □ Drill Guide □ Drill Draw - fiiil - 181 Keep Outs Ill IZl Multi Layer !iifil - M - - Rats Nest Selections CJ Background ech 1 D Mech 4 IPoslScript Printer on LPT1: D Bottom D Batch Mode I [Silks Bottom - . IZl Tc 0 IZl Grid 211tiJ Seperate Page For Each Print 0 Composite Print ® Panels (Multiple Layers Per File} Border Between Prints ~ at the same time, using standard Windows routines, to move iriformation between different files or different applications. The Prate! for Windows family consists of Advanced PCB - - ~--~ IZ] Transparent Ill D Mech 3 lll.ll D Dithered Colors ech 2 - IZ] Bottom - rsMT Paste Mask LD Top D hanical Layers ! Solder Mask I D Top □ DRC Errorsfiiil IZ] Grid 1- CJ fll CJ - □ Mid14 (Ill Visible- advanced level PCB layout - $1990. Options: Advanced Place $995 , Advanced Route $995 . Professional Schematic' - schematic capture -$129,.5. Option: Digital Simulator• $795. ■ Protel Technology Pty Ltd PO Box 204, Hobart Tasmania 7001 Phone (002) 730100 Fax (002) 730944 Tollfree 008 030 949 T?! chnology ~Available April 1992. Prate/ is a registered trademark. Admnced PCB and Professional Schematic are registered trademarks of Protei Technology Pty Ltd. V1indows is a registered trademark of Microsoft Corporation Inc. 60 SILICON CHIP 4MHz, although I considered the possibility that this may be only a nominal value. Initially, I had some ideas about trying to find out exactly what had gone wrong but the more I delved into the problem, the more complex it became. For one thing, what was the precise intended frequency of the crystal? Was it exactly 4MHz or merely something very close to it? On the basis of a simple sequential 2:1 division chain, a 4MHz crystal is not practical. But 4.194304 will divide exactly to lHz, or 3.932160 will divide exactly to 60Hz, either of which can form the basis for a clock display. But the simple 2:1 sequence is not the only option. Modern chips can provide virtually any order of division and it is quite conceivable that the makers used a more complex network in order to accommodate a standard 4MHz crystal. These are used extensively in computers and are quite cheap. The situation was further complicated by the virtual impossibility of making an accurate crystal frequency measurement directly across it. Any connection here would load the crystal and make the reading meaningless. Significantly, several computer buff acquaintances have told me that they have similar problems with the realtime clocks in their personal computers. In all cases, their clocks run fast. One enthusiast, who uses the clock mainly to maintain the calendar, realised recently that, since he had last set it, it had gained 17 minutes! I finished up using the more or less brute force approach of loading the crystal circuit with additional capacitance until an acceptable result was achieved. The circuit shows two 33pF capacitors, C152 and C153, connected from each side of the crystal to chassis. I decided to add some capacitance in parallel with each and started with two 13pF units, tacked on under the board. This came out better than I had hoped. Not only did the crystal accept the idea - they can sometimes drop out or behave erratically with excessive loading - but the error was significantly reduced. The clock went from gaining five minutes in 24 hours to losing about 25 seconds over the same period. Electronics Workbench® 66660660 Build and simulate both analog and digital circuits, complete with simulated instruments on your computer! FEATURES • Quick and simple circuit entry • Digital and Analog Modules included, complete with all components • Simulated instruments: dual trace scope, spectrum analyser, function generator, multimeter, digital word generator and logic analyser • Complete control over all component values and parameters • Print: circuit schematics, parts list, instrument readings, macros • Logic conversion -truth table to Boolean formula to logic gates • Customisable hypertext help system THREE VERSIONS • Professional Version: EGA/VGA colour display; unlimited components • Personal Plus Version: Monochrome display; unlimited components • Personal Version: Monochrome display; limited to 20 ----------------I YES ■ Something logical OK, so I had overshot slightly and needed to decrease the additional capacitance. A small trimmer seemed to be a logical alternative at this stage. I didn't have anything suitable in stock but, while looking for something else later on, I found an old VCR board with a miniature trimmer across a crystal. It was close to ideal. It measured from 7-20pF and needed only minor doctoring of the leads to make it suitable. I removed the 13pF fixed unit from C152 and fitted an 11 pF capacitor in its place. I then fitted the trimmer across C153. Over the next few days, I juggled the trimmer on a trialand-error basis and eventually reduced the error to a couple of seconds a day. And that's probably as good as I will do, because there does seem to be some drift which is probably due to small variations in the trimmer's value. A better quality unit ::nay help but would be hard to justify. Well, that's it for this month. If I learn anything more about this set, I will pass it on. SC ~ want ELECTRONICS WORKBENCH m my computer $429 $299 $149 Professional Version Personal Plus Version Personal Version Plus $7 Delivery Enclosed is my cheque/money order for $._ _ _ _ _ or Please debit my Ca rd No.I J J O J J O Bankcard J J J J J J Mastercard J J J J J I Signature _ _ _ _ _ _ _ _ Expiry Date _ _/_ _ Name _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ Street _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ Suburb/Town _ _ _ _ _ _ _ _ Postcode _ __ Send to: Emona Instruments, PO Box 15, Camperdown, NSW 2050. ~-----------------· Tel: (02) 519 3933 Fax: (02) 550 1378 FEBRUARY1992 61