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SERVICEMAN'S LOG VCR tape transport problems I suppose that it's inevitable that a device like a video recorder, with its complex tape transport system, would have more than its fair share of mechanical "funnies". Some day, no doubt, we will have all electrical recording systems, with no moving parts and no need for service. (Oh yeah!) In the meantime, from the real world, here are a couple of VCR stories involving transport problems. The first was a Sharp VC-9300X from one of my regular customers. It came in with the stated fault that it would -load a tape but refuse to play it. Transport problems can take many forms and the word "play" is often used quite loosely by some customers. Sometimes they mean it literally and sometimes they mean that the tape will load but not rewind (ie, if the tape is partly used when loaded) . Or they can mean that it will load but not fast forward , or that it will load, start to play, and then foul up and chew the tape. Getting the true picture can call for some tact. Fortunately, there was no real confusion in this case. The owner's description was correct; it would load but not play. However, it could fast forward and rewind normally. A visual check with the covers removed showed that it was attempting to function in the play mode but was forming a loop of tape. Idler wheel assembly Most transport problems, including those mentioned above, can be traced to the idler wheel assembly; an arrangement which, with minor variations, is used on most machines. So, when trouble strikes, it is always replaced as a routine first step. Even if it proves not to be the trouble, it is a worthwhile service for any machine more than a few years old since the component cost is quite low. The loop of tape is a classic symptom. If the idler mechanism fails and deprives the take-up reel of drive, the loop of tape forms until the take-up reel sensor informs the microproces- TETIA TV TIP AWA C620 (G chassis) Symptom: screen shows a small, bright raster, with all four sides curved inwards. There is no sign of convergence on the screen. The bottom edge of the picture shows severe vertical foldup and the whole picture is covered with flyback lines. Cure: In spite of the complex nature of the symptoms, the fault is quite simple. It is caused by the loss of 54 SILICON CHIP the 150V rail. The usual reason for the loss of this rail is that D575 (UF2) goes short circuit and takes out safety resistor R581 (4.?Q 0.5W fusible). A DYX55/600 makes a good substitute for UF-2. 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. sor that the take-up reel is not moving, at which point the system shuts down. And so I changed the idler wheel, noting as I did that the old one was looking rather tatty and really needed changing anyway. I also went over the system with the torque gauge. The fast forward and rewind torques read 800gm plus, which was well within tolerance, as was the take-up reel torque in the play mode at around 175gm. But all this was cold consolation when I tried the machine again and it behaved exactly as before. It was only then that I took a closer look at what was happening and, in particular, at the exact nature of the tape loop. And what I saw was something which, in theory, couldn't really happen; the tape loop was forming ahead of the capstan. This should not happen because there is nothing to propel the tape at this point in the transport system. Nothing in theory, that is. What in fact was happening was that the capstan mechanism had failed and the tape was being propelled by friction from the drum. So why had the capstan failed? The most likely possibility would normally be a broken capstan belt but this was clearly not the case. What's more, if it had been simply slipping, there should have at least been some propulsion, however erratic. Well, the short answer was that the capstan shaft had completely seized in it's bearing. The capstan shaft and flywheel assembly is held in place by a thrust bearing on the underside of the flywheel. This in turn is mounted on a short bar held by a couple of screws. Removing the screws and the bar allowed the capstan assembly to be gently worked free in the bearing and then withdrawn. The best way to describe the shaft · was that it was "gummy"; apparently as a result of the original lubrication having dried out. This is the first time I] -. - J.. G .. Cc • 0 g;i......., • .___ MOS, 1"'MN~'PORT 'PROB>LE:.MS ;.._,CAN Bt:: "'1""-RACt;:.1) ,-o fHE:: \t)LE'.-1<- W\-\E.E:L ~'SSE.t•l\"BL'Y ------P..'S USE:P ON MOST t-1\f:\C'r\lNE.S~•• I have encountered anything like this and just why it should have happened is something of a puzzle. Was it the original lubricant but which, for some reason, was incorrect (did someone used the wrong oilcan)? Or had someone been there before me and used the first lubricant that came handy? Fortunately, there had been no actual damage to the shaft or bearing. I cleaned them up, re-lubricated them, and put everything back together. And that was all it needed; everything functioned like new and the machine was returned to the customer. That was several months ago now and there has been no word from the owner since. Another Sharp The second machine was another Sharp, a VC-782X, which came in quite recently. In this case, the fault was quite erratic and much more subtle. This particular VCR belonged to one of my long-standing customers, although the machine had not been serviced for about four years. The lady of the house dropped it in and gave a fairly detailed description of the fault. According to her, the machine would play normally for most of the time but every so often it would go into what she described as the "pause" mode. And to back up this description, she had brought in a tape on which this fault appeared. At the first opportunity I connected the machine to a monitor and played the customer's tape. It ran for about an hour before anything happened and then it was so fleeting that one rieeded to be quite alert to notice it. In fact, all that I could be sure of was that there was a glitch of some kind in the sound. I continued playing the tape and, towards the end, it was misbehaving quite frequently. Sometimes it was quite brief; similar to the effect described above. At other times it was much longer; it would pause for two or three seconds , five seconds, and close to 10 seconds on one occasion, but never longer than this. During these longer periods, when I had time to look at the screen, there was a stationary image, with noise bars and some jitter and, of course, no sound. Two aspects of the problem had me stumped at this stage. By what mechanism could such an effect be recorded on the tape, as the customer had implied. Indeed, was the fault really in the record mode, or was it only present during playback? In an effort to clarify this point, I took the customer's tape and put it in a known good machine, selecting the last part of the tape where the fault had been the most obvious. Unfortunately, the results were, as they say, inconclusive. There were still some glitches but they were not as frequent as in the previous run. Nor could I be sure that they all occurred in the same parts of the tape, which made things rather confusing. One problem with tests of this kind is that it is seldom practical to sit down in front of the monitor and give it one's undivided attention for several hours at a time. In real life, such tests have to be made while routine jobs are being handled. But had I been able to give the setup my undivided attention, I may well have learned something more about the fault and tracked it down sooner. But that's with the benefit of hindsight. As it was, it did seem that the fault was common to both the record and replay modes. At this stage, I decided to try one more trick. I turned the customer's machine on again and loaded it with a known good tape of my own. Well, I thought it was a good idea but, after three hours without so much as a flicker or a click, I was more confused then ever. In desperation, I rewound the tape and ran it again. And at last I achieved some kind of result; after another two hours ofrunning (a total of five in all), it suddenly went into fault condition, coming up with several pauses, one after the other. It was relatively severe in terms of frequency, although the effect was quite brief - only a few seconds - in each case. Our loss i your gain Fracarro's ESVU2. The really low loss VHF/ UHF mixer with areasonable price tag. Peter C. Lacey Services Pty. Ltd. P.O. Box 678 (74Fulton Ad.} Mount Eliza 3930 Tel:03 787 2077 Fax:(03) 787 3460 ACN006893438 MARCH 1992 55 Video Recorder Faults Well, th at confirmed that the trouble could occur in th e replay mode, while my previous checks had indicated that it could also occur in the record mode. And of all the functions which were common to both, the transport system was the most likely suspect. But an other thought had emerged from all these tests; it w as possible that the fault was temp erature conscious an d appeared only after th e machine had been running for som e time. But w hat was it? As already mentione d , my favourite susp ect is th e idler wh eel, although I was h ard put to rationalise this with all the observed symptoms. Nevertheless, I decided to ch ange it; after fo ur years, a new one wouldn't go amiss. Which is what I did . I th en ran th e known good tape through it again an d it behaved perfectly - as it did a second time , and a third time, and a fourth time. In all, it ran perfectly for close to 12 hours , from when I started in the workshop early in th e morning until I gave it away in th e late evening. Had I fix ed it? I would have liked to have thought so but I wasn't prepared to believe that on such evi den ce . So I put the machine through anoth er sequence of tests , this time alternately recording and replaying th e tape on a 3-hour basis. And the prolonged running did eventually pay off; the fault returned. But this time I was a ju mp ahead; I had removed the bottom cover an d turned th e machine on it's side so that I could observe its beh aviour from both the top and the bottom. So when it started to play up this tim e, I was ready. And I soon had the answer; by observing th e flywheel I cou ld see that the cap stan was stopp ing briefl y whenever the fault occurred . Well, that was a major breakthrough, even if I still h ad to find out exactly why. My first suspect was the capstan motor; did it have an intermittent fault? I managed to get my finger onto it, so that I could feel it running. An d that cleared it; it was still running when the system baulked , with th e belt slipping on the pulley. That left only one possibility in my book. I pulled the capstan/flywh eel 56 SILICON CH I P assembly out of its bearing and examined it closely. And there was th e faint brown stain signifying the same gummy substance that I had found in th e other Sharp machin e s everal months previously. Only this time it wasn 't bad enough the stop the shaft permanently; just briefly and , I suspect, when the temperature rose after prolonged use and th e metal expanded. And n ow, w ith hindsight, the symptoms I h ad observed began to make sense - not that this was much use now, although it might help in the future . But had I been able to give the screen my undivided attention, I would have seen that there were two quite diffe rent effects . Wh en the capstan jammed in the record mode, several seconds of recording would be lost, causing a jump in both m ovement and sound on playback, exactly the same as the effect caused by chopping several frames out of a p iece of film. It was quite fleeting and I only ever observed the sound discontinuity; by the time I looked to the screen, it was all over. In fact, depending on just where this happened in the program, it could even sometimes go unnoticed. But when the capstan jammed in the replay mode, the effect w as quite different. We now had a froz en frame, exactly as in the pause mode and, of course, n o sound. So it w as all very easy to explain in hindsight. But they were very deceptive symptoms at first en counter. Letter from NZ And n ow, for a change of scene but not the subject - here are some comments prompted by a letter from a reader, Mr K. M. of Silverstream, New Zealand. It is reproduced - in slightly edited form -in the accompanying pan el. I suggest that you read it first. There w ere three other pages accompanying this letter. One was a copy of a letter to the service company, complaining bitterly about the failure of the company to provide adequate service and solve the problem. The oth er two - amounting to a little over one A4 page of typed material were copies of the machine's fault The attached fault record and my response to a service com pany here in NZ details a number of problems I have had with my video recorder. Would you consider forwarding it to the Serviceman, perhaps for any comments he may care to make. (He may ignore it, or use it in the column if of any use) . I ran out of time on the last fault (intermittently failing to load) and I feel let down by the particular service company, who virtually ignored al l the information I provided them and didn't adopt the right approach , or make any real effort to locate the fault, or substitute any parts! I have regularly admired the SILICON CHIP serviceman 's perseverance on "the dreaded intermittent" and, "sure as eggs", the fault on my machi ne wi ll be back! I neither expect a "free fix", or a "remote fix", but the Serviceman probably knows off the top of his head the likely causes (ie, parts which could be swapped or substituted) of the fail ing to load fault, or possibly the whole series of faults. The faults may make the basis of a segment in the column, if the Serviceman knows what may cause such a sequence of faults. The machine has always had the intermittent quirk of sometimes not recording on timer record. Probably it didn't load and the micro shut it down . K. M., Silverstream, New Zealand. h istory which went to the service company. Unfortunately, space does not permit reproducing all this but I will comment on extracts from it as I proceed. Mr K. M. 's probl ems ar e best divided , initially, into two categories : the purely technical problems, on which h e has asked m e t o comment , and the problems w ith the service . organisation. Let's look at the technical problems first . The machine is a National/ Panasonic NV-85 0 video recorder. This particular model first appeared about eight years ago and was one of the first with stereo sound recording. I am happy to offer any advice or suggestions which I can but, as can b e appreciated, at this distance that is all they can ever be. If they h elp, that's fine. The machine appears to have suffered from three separate faults. The first, according to K. M. , has always been present; an intermittent failure to record in the timer mode. The second apparently occurred after a mains supply failure and was traced , by K. M., to low 5V and 12V rails. The 5V failure was traced, in turn, to an open circuit ¼ W fusible resistor, R1001, in the 14V rail, which supplies the 5V rail. Failure of the 12V rail presents something of a mystery; and in more ways than one. For a start, there are two 12V rails in this model, both derived from the same 18V unregulated rail but otherw ise quite separate. It is not clear from K. M.'s letter which of these two was involved. More importantly, th e cause of failure ap pears not to have been found; it apparently came good spontaneously after an ohmmeter check for a short circuit. K. M. suggests that the ohmmeter voltage performed some kind of "bootstrap" function. The third fault , and the one for which the machine was submitted for service, was intermittent failure to load a tape. For a number ofreasons, I will comment on this fault first. K. M. made a number of observations regarding it, which he set out in the screed to the service company. I quote in part: "The loading cycle commences OK , with the tape extracted and wrapped around the drum. However, the capstan roller, which is operated (held) by a spring but released by a mechanism driven by the lower loading motor, does not engage the tape and capstan. The problem appears to occur when the machine is w arm. "I replaced the capstan belt, with no effect. My pick would be to replace the load motor belt but I don't have one. In fact, I replaced this about tw o years ago". Well, that is a n ear perfect description of a classic fault. An d, ironically, it is almost certainly due to a belt failure - the very belt that hasn't been ch anged. The condition of this belt is quite critical; it needs only a small deterioration in order to produce exactly those symptoms. In sh ort, if a machine turned up on my bench with those sym ptoms, the first thing I would do would be to change the belts. And I used the plural there deliberately; I would order a complete set of belts and replace the lot. Th ere is n o room for mucking about w ith belts; once on e gives signs of trouble, th ey sh oul d all be changed. The material cost is small - relative to any service charge - an d it might as well be don e wh ile the machine is open. And it minimises the risk of another failure in a few months time. I ch ose to comment on that fault firs t for a couple of reasons. One was simply because it appeared to be the one with the most obvious explanation. Another reason was that K. M. advanced the theory that the fai lure to record on timer was due to a failure to load. I don't totally subscribe to this theory - although it can't be ruled out - but if it is valid, then replacing AUSTRALI AN MADE TV TEST EQUIPMENT 10% discount on all test equipment. 15% discount on two or more items. Built-in meter to check EHT transformers including split diode type, yokes and drive transformers. $78.00 + $4.00 p&p TOROIDAL TRANSFORMERS Built-in meter reads positive or negative voltages from 0-S0kV. For checking EHT and other HT voltages. $98.00 + $5.00 p&p Strong magnetic field. 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 Designed to test infrared or ultrasonic " contro l units. Supplied with extension infrared detector lead. Output is via a LED and piezo speaker. $84.00 + $4.00 p&p _,, ,.__.---~ = ~ _-::,::--,-'7:·--J'J'+-"v"' -~ 2 TUNER REPAIRS ~ pFf~;1p!~; ~xpc~~~ge -~ Cheque, Money Order, Visa, Bankcard or Mastercard 216 Canterbury Rd, Revesby, NSW 2212, Australia. Phone (02) 774 11 54 Fax (02) 774 1154 • • • • Now made in Australia Standard range ~ SVA to 2kVA Large ex-stock quantities available Competitive pricing available fo r OEM s & 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 MARC H 1992 57 SERVICEMAN'S LOG - CTD the belts may kill two birds with the one stone. So what is my theory about the timer mode recording failures? My first suspect would be an intermittent - probably a dry joint - on the timer board or the timer operations board. The timer board is on the right hand side of the machine, immediately behind the clock, lying flat under the main cover, and readily accessible. The timer operations board is on the front of the machine and carries the clock display. Having said that, I must concede that finding the actual fault is not likely to be easy. But that would be the first place to look. That brings us to the original power supply failure. Once again, the failure of R1001 is a classic fault. Another common offender in this area is Cl 101, a 3300µF 16VW electrolytic on one of the 12V rails. C1103, another 3300µF electro, rated at 25V, on the 18V rail can also give problems. In view of the rather dubious cure of the 12V rail failure in this power supply, I would suspect that Cl 101 might be intermittent (I am doubtful about the "bootstrap' theory). Well, those are the three faults, dealt with as best I can on an individual basis. Of course, I could be wrong; but those are the best suggestions I can offer at this distance. I hope they help. The service company So much, then, for the technical problems. What about K. M. 's other problem; the quality of service provided by the service company? This is even more difficult to evalu- 58 SILICON CHIP ate, at this distance, the more so because I have heard only K. M. 's side of the story. Nevertheless, his complaints would seem to justify some comments, at least of a general nature. It would be unfair to identify the company concerned, although a colleague who visits relatives in NZ, tells me that they are a large organisation, with several branches throughout the country. So what exactly is K. M. complaining about? As he sums it up in his letter to SILICON CHIP, "I feel let down by the particular service company, who virtually ignored all the information I provided for them, and didn't adopt the right approach or make any real effort to locate the fault or substitute any parts!" In greater detail, it appears that K. M. submitted the machine and, as he puts it, "had gone to some trouble to detail not only the current fault (it intermittently wouldn't load) but also previous faults which had recently occurred" (the above-mentioned two pages of fault history). He complains that, in spite of this, he had to ring the company to explain the nature of the fault and that the booking clerk wanted to reduce the complaint to one or two words; suggesting "no colour". Several days later, he rang and asked to speak to the technician but he was not available. He rang again three days later but; again, he was not available. The technician was finally contacted another two days later and reported that he had been running tapes through it regularly but could find no fault. At this K. M. protested that this was no way to find a loading fault and suggested that it be put through a series of loading sequences. This the technician agreed to do. Two days later, he again contacted the technician who told him that he had been unable to create the fault. So K. M. elected to take the machine back. The firm then submitted an account for $33.00. And that is, of necessity, a condensed but, I fee l, fair summary of the situation. What went wrong? So what went wrong? Lack of communication , basically. And who was to blame? Both parties, to some extent, but the major offender was the service company. They are suffering from an attitude which has been with us for almost as long as there have been servicemen but which I had hoped was dying out. Unfortunately, my colleagues assure me that it is well and truly alive and kicking. I refer to the isolation syndrome; the barrier which such organisations erect, doubtless on their accountants' advice , between the customer and the technicians. It is apparently based on the concept that nothing must be allowed to interrupt the smooth flow of production line servicing. So the customer is greete d by a non-technical booking clerk, arined with a set of stock phrases which are supposed to cover all the likely faults that a piece of electronic equipment is prone to. There is no provision for the multitude of way-out, never-heard-of-before, faults which, as any serviceman will confirm , are par for the course. And the word "intermittent" has never been heard of, or is too hard to spell. Hence the ridiculous situation where the booking clerk wanted to classify K. M.'s problem as "no colour", when this was as far from fact as it could be. Accountants & ivory towers But this is something which the accountants , in their ivory towers, cannot appreciate. Suggest to them that they should employ someone with some technical knowledge as a booking clerk and they would scream , "too expensive. Can't afford it." The truth is, they can't afford not to if they value their reputation. This sort of communications barrier is the main cause of ineffective service , misunderstandings , customer complaints , and, ultimately, protests to the Consumer Affairs Bureau - to say nothing of the w ord-ofmouth publicity which can be so damaging. And this is where the one-man organisation , with its sympathetic, face-to-face approach to his customers , leaves them for dead. OK, so much for the company's faults. What di d K. M. do wrong? I think he tried too hard. Probably in anticipation of the problem I've just discussed, he tried to make sure that he presented every fault detail, past and present. And I suspect it was too much; that the technician had difficulty in differentiating between past and present faults and finally tossed the whole screed to one side. Granted, a well run organisation should have been able to cope. But they didn't. And, finally, I feel that the technician should have been prepared, and been allowed, to pursue the fault for longer than two days, after it was clear exactly what he was looking for. I would certainly want longer than that. And that's about all I can say, looking at it from this distance. SC Electronics Workbench® • C . 0: ..... :_ ' 0 ii i. ;. - ---, - - -- '., ].,.: I• - - ~ T~, ..... . . [!;] =~--'_-,_:-~ _;.. ........ _ _ ___, I : .I j uU" N" c. j - --"------------ , 0 , 606606 66 "'"" r:;;-_ Build and simulate both analog and digital circuits, complete with simulated instruments on your computer! 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