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VCR: Very Crook Recorder According to popular philosophy, we are supposed to learn by our mistakes. On this basis the cynic in me would suggest that I must be a very learned person because, in this game, there is plenty of room for mistakes. However, modesty for bids such an admission. This story concerns two General Model VGX-510A video recorders and two rather tricky faults which I encountered in them. One is a fairly routine fault, though more or less confined to this model, while the other may well have been a one-off. Nevertheless, it was a Very Crook Recorder. But before delving into the technical side of things, it might be helpful to list some of the brand names and cross company relationships which come to mind when this model is mentioned. And it is a rather complicated situation. First off, the General VGX-5 lOA is also marketed under the Palsonic label, model VCR-5000. However, the same deck is used in at least five other models: the JVC HR7200EA (for which it was originally designed), General Electric GEV6900, Ferguson 3V29A, Rank RV340 and some NEC models. So we have the same deck in at least seven different brands - a point worth noting for future reference. To make things even more confusing, the General machines have used parts from a variety of other manufacturers. For example, while. the VGX-5 lOA uses a JVC deck, the more recent General VGX-540A uses the the National NV-370 deck. In fact, the General organisation, having been gobbled up in some kind of a takeover, is now known as General Fujitsu. Well, so much for the corporate affairs side. Let's get back to technicalities. Mention of the JVC 70 SILICON CHIP 7200 might remind some readers that I dealt with a tricky problem in one of these machines some 12 months ago, in April 1988. Reference to those notes may help in following this story. I should also mention that most of these machines are now at least five years old. The first fault in the General VGX-510A showed up as damaged tape. More specifically, the tape was crinkled along one edge usually the Jower one - but in a few cases both edges of the tape were affected. The effect varied from machine to machine. In most cases it was minimal, probably because the customer sought my help early, but in some cases it caused tracking and sound errors. In any case, it was something which could not be tolerated, particularly if the machine was used to play hired tapes. My first attempts to cure this This photograph of the pinch wheel clearly shows the wear which caused fouling of the capstan. fault were a dismal failure. Having never struck it before I assumed that it was most likely a fouling problem; a build up of oxide on the various guide posts and rollers. And in fact, the build up was considerable. Unfortunately, a thorough cleanup of all these parts did little to alleviate the problem. Next I checked the various adjustments which I thought might have some bearing on the problem but found nothing suspicious. Puzzled, I put the machine to one side while l thought about it but before I could reach any conclusion, a second machine appeared on the bench with the same problem. Crook pinch wheel I decided it was time to ask for help. I rang the General service department and put the problem to them. The technician at the other end didn't hesitate: "change the pinch wheel". And that was it - he didn't elaborate and was so positive in his statement that I. didn't seek elaboration. In fact, he wasn't wrong but he'd left a lot unsaid. Anyway, I went ahead and ordered a stock of pinch wheels and when they arrived attacked the first machine. And this was when I realised the real nature of the problem. In order to replace the pinch wheel it is necessary to remove the cassette carrier assembly from above the deck proper and this gave me a much better view of both the pinch wheel and the associated capstan shaft. And that's where the real trouble lay; on the capstan shaft. It's not possible get a good look at this shaft when the cassette carrier is in place and it was now obvious that my attempts to clean it had been quite futile. To tell the truth, I hadn't paid all that much attention to it, previous experience being that this component collects very little oxide. So a token wipe, more or less blind, with alcohol soaked tissue was all it had received. Now that I could see it properly I realised that it was the worst case of fouling that I had ever seen. More to the point, it wasn't the conventional oxide fouling. There were two black rings on the shaft, the width of the tape apart and quite hard. The only place this fouling could have come from was the pinch wheel and this was confirmed by the manner in which the pinch wheel was worn. So the technician had been right but he had failed to mention the side effect of the worn pinch wheel; ie, the fouling on the capstan shaft. Anyway, I fitted a new pinch wheel and then tackled the capstan shaft. As I said, the fouling was a hard encrustation and while in theory it should not have been narrower than the tape width, some of the muck had crept into this area. Hence the tape damage. Getting it off wasn't easy. I hesitated to use excessive force for fear of damaging the capstan shaft surface yet initially it seemed impervious to the alcohol I normally use or the other solvents around the shop. However, it did yield eventually and I had a nice clean capstan again. And that was it. The machine behaved perfectly, with no hint of tape damage. The second machine also received the same treatment a.nd it responded similarly. Since then I have encountered the same problem in a number of these machines. Some came in because of tape damage, some for other faults but having learned my lesson, I give them all the treatment. At the same time, I take particular care to examine all other machines passing through the workshop for the same fault. Arising out of this exercise is the conclusion that this is a very serious problem with these machines, apparently due to the material used in the pinch wheel. Whether this was only a batch problem, or whether it will continue, I cannot say. All I do know is that every machine of this model should be ex- amined for this fault as a matter of course, regardless of any other fault. The other point is that, so far, this appears to be the only deck .with this fault. A few other machines have shown a hint of the problem but nothing like the gross fouling encountered on these. So there it is - I will be keeping a closer watch on all machines from now on. Fault number two So that was fault number one with this model. Fault number two turned up a few months later after I had treated several more machines for fault number one. In fact, it was for fault number one that this latest machine came in and I simply took it for granted that it would be just another routine job and quoted the customer accordingly. And that's all it was initially; exactly the same fault needing exactly the same treatment. It wasn't until I had put everything back together and given the machine a routine test that I realised that I still had problems. Sure, it was no longer damaging tape but there was a serious tracking problem wfrh noise bars on the picture and a problem with varying sound levels. For some reason this latter effect seemed to be worse on tapes which had been recorded on this machine, rather than on pre-recorded tapes. Even so, I wasn't particularly worried. I imagined that a normal setting-up routine, involving height adjustment of the guide roller assemblies, would be all that would be needed. It is a fairly straightforward routine, although it is a bit fiddly and time consuming. It is sometimes referred to as the "Interchangeability Adjustmenf'' CRO patterns The routine is basically the same for all machines. Some dismantling is involved to gain access to two test points normally located on the main board - test points five and three in this machine - and these are connected to the CRO. Test point five delivers an RF envelope pattern from the video heads while test point three delivers a 25Hz square wave which is used to lock the CRO timebase. The machine is then loaded and run with a standard colour bar tape. Assuming correct adjustment, r Q _J ·-== ==-----!' •' ol 0 ~ Q '".-0 'G, • o-() -·- ~A SOtl\~ MA~il-\~ G \ S I NVOL.Ve:t,•. . APRIL 1989 71 Envelope level is dropped at the beginning of track. I: : ::[::: J Fig.I: this line drawing and CRO pattern, from a National manual, illustrate a severe tracking error. A mirror image of this pattern may also occur. this setup should deliver a rectangular pattern to the CRO. If it doesn't, the height of the two guide rollers has to be adjusted until this is achieved. At the same time, it may be necessary to adjust the height and azimuth of the sound/ control head to give the best sine wave from the audio test tone on the tape. These adjustments tend to interact and may need to be repeated until both are correct. In greater detail, the CRO pattern displays the output froin the two heads and most importantly, the transition point where one head takes over from the other. In the case of a new machine (or a new set of heads), the output from each head should be an almost perfect rectangle and the transition point should be almost invisible (Fig.2). But if the tape is not tracking properly, or if the heads are worn, the rectangular pattern will taper off at one end or the other (see Fig.1). In fact, it's possible to recognise which guide roller should be adjusted according to whether the taper is to the left or right. Well, that's the theory and it usually works out well in practice. 72 SILICON CHIP Envelope is adjusted properly I I : L: I Fig.2: this diagram shows what the pattern looks like with correct tracking, assuming that the heads are in good condition. The result is sometimes less than perfect when the heads are worn and one must then settle for the best compromise and hope that the end result will be acceptable. If it isn't, a new set of heads is the only answer. Anyway, I went through the procedure and the CRO presented a perfectly acceptable pattern, at least initially. The snag was that the machine wouldn't hold this adjustment; while one watched, the rectangular pattern would suddenly drop at a transition point and noise bars would appear on the screen. I went over the procedure again but with no more success. Clutching at straws, I went through the sound/control head setting up routine. Significantly, it didn't seem to need adjustment and in the end had no worthwhile effect on the problem. Well, to cut a long story short, I went through the video head routine about umpteen times, interspersed with checks on any other components or adjustments which I felt could be important. I drew a blank all round. In the end I had to admit that I was going round in circles, getting nowhere. It was time to ask for help again. So I made another call to the General service depa rtment. This time I found myself talking to a Japanese technician who seemed t0 be particularly well versed with this machine. He listened very carefully to my explanation of the problem and the steps I had taken so far, checked whether I had done this or that, and was finally forced to admit that I had done all the right things. More to the point, he couldn't think of anything else that I could try. In short, he wa s as puzzled as I was. In fact, he went so far as to say that, considering the age of the machine, it might be more economical to write it off, rather than chase such a difficult fault. I did raise the matter of the guide roller assemblies but he was most emphatic that he had never encountered any problems with them. As far as he was concerned, the guide rollers simply did not give trouble. It's all there is So I was back to square one. I put YOU NEED THIS TV TEST EQUIPMENT Slant pole Guide roller Supply pole base ~ 0 Supply loading ring Pin slide ring SHORTED TURNS TESTER Including meter for checking EHT trans, yoke windings, drive trans. $78.00 + $3.00 P&P HI-VOLTAGE PROBE Fig.3: the guide roller assembly and its relation to the loading rings. Additional information on this assembly was published in the April 1988 issue . Including meter Reads positive or negative 0-50kV For TVs, microwave ovens and high voltage equipment $84.00 & $5.00 P&P the machine aside again until I could spare the time to really get stuck into it. In the meantime my thoughts kept coming back to the guide roller assemblies; I couldn't shake off the idea that this was all there was left to suspect. Eventually, I found time to set everything up as before and repeat the adjustment routine once again. Initially, the results were exactly the same. The breakthrough came when, more or less on impulse, I applied gentle pressure with the blade of a screwdriver to the top of the guide roller assembly on the supply reel side. The result on the CRO pattern was immediate and I found that judicious pressure could produce and maintain an almost perfect pat- The Very Crook Roller which caused the trouble . While known to be faulty, no slackness could be detected in the assembly. tern. But once I withdrew the driver, we were back to square one again. I wasn't sure whether this was normal or not, so I tried the same tactic with the guide roller on the takeup side. The result here was quite different. Short of applying extreme pressure, it had virtually no effect. From this I assumed that there was some slackness somewhere in the suspect guide roller assembly. Yet try as I might, I couldn't pinpoint it. All I had established was that one roller responded to pressure and the other one didn't. The only way to prove the point was to replace the roller. Well, that seemed simple enough - I thought. I turned to the manual to find the appropriate part number and realised that the assembly, as such, was not listed. Each component of the assembly - there were seven in all - was listed separately with its own part number. Fair enough; all I had to do was list these numbers and ask for the complete assembly which comprised them. And that was the first barrier. I rang the spare parts department, told the assistant what I wanted and dictated the part numbers to him. He asked me to wait on while he punched them into the computer, then announced that, as far as the computer was concerned, there were no such part numbers. Mentally muttering "Don't be Uncle Willie", I made the more diplomatic suggestion that perhaps he should check further, as the part numbers were listed in the manual. The upshot of this was that he pro- TV TUNERS (PHILIPS) ECL 2060 Repair or exchange UV461 Repair only $17 .00 ea + $2.00 P&P CHEQUE, MONEY ORDER, BANKCARD OR MASTERCARD TO Y.V.TuNERs) 216 Canterbury Road Revesby 2212, Sydney, Australia Phone: (02) 77 4 1154 SALES CAREER IN ELECTRONICS Suit bright young electronics enthusiast 19 to 24 years. The wholesale division of Altronics has opened sales offices in Sydney and Melbourne. We have a position in each city for a sales person who fits the following: ( 1) Is a pleasant person who gets on well with others. (2) Wants to "get on" in life & possesses self-motivation. (3) Has own vehicle - we will pay a generous mileage allowance. (4) The position will involve regular calls to clients (ie, electronics firms, manufacturers , contractors and resellers), as well as office operations; eg, handling telephone enquiries, sales and the like. The successful applicants will be 2nd in charge to the state manager in each city. A generous salary and commission system applies. Sydney applicants call Colin Fobister 437 4077. Melbourne applicants call Brian Sorensen 811 9967. AL TR0NICS DISTRIBUTORS PTY LTD, Dynamic suppliers of electronic products and components. 174 Roe Street, Perth, WA 6000. APillL 1989 73 may be a one-off event. Ifso, that's fine. But the mere rarity of. the problem is itself a hazard; there is nothing on record which will help. Let's hope this story rectifies that. And who knows; it might even save a machine from being written off. SERVICEMAN'S LOG Foreign bodies .. . r \ H-~Ve: 'De:s~R\'8~ A VA'R\E:"'t"{ OF FOR~lGt\l "BODIES I HAV~ F\~He:'D ovr OF mised to look into it and ring me back. And he was as good as his word, except that the call came not from him but from the Japanese technician I had spoken to earlier. Not realising who I was, he started out by explaining that they didn't keep this assembly in stock. (I assumed that this was a continuation of the previously expressed idea that they never needed to be replaced]. Then he went to enquire why I needed this assembly. At this point I reminded him of our previous discussion and explained that I was now virtually certain that a faulty guide roller assembly was to blame. And I gave him a detailed account of what I had done. My experience obviously came as a surprise but having listened carefully to all I had done, he seemed to be convinced that I was on the right track. On the other hand sup74 SILICON CHIP v,~ RECDR~S plying a replacement was still a problem. In the end, he said, "Leave it with me, I'll see what I can do". So we left it at that. Sure enough, a couple of days later a replacement assembly arrived in the post. I have little doubt that it had been raided from another machine, probably one written off for some other reason. I lost no time in fitting the new assembly and going through the whole setting up procedure again. And to my immense gratification, it worked. The CRO pattern was rock steady and the picture completely clean. So I'd not only cured the problem, I'd proved my point and found a new meaning for VCR: Very Crook Roller. I have no doubt that the technician was being perfectly honest when he said that there was no history of failure; which is why I suggested at the beginning that this And now here is something in lighter vein. On a number of previous occasions I have described a variety of foreign bodies that I have fished out of malfunctioning video recorders; parts of children's toys, coins, matchsticks, beads and so on. So what was there left? Read on and see if you can top this one. It all started with a phone call from a lady who explained that she had a new Panasonic (National] video recorder which had performed perfectly for the first few months but was now giving trouble. She was somewhat vague about the exact nature of the fault but I gathered that it was basically a loading problem and there was something about a loop of tape remaining after a cassette was unloaded. Anyway, I suggested she bring the machine in and we would give it a once over. She then raised the matter of warranty, pointing out that, as the machine was only six months old, she assumed it would still be covered. I assured her that this was so. So, a few days later the lady pushed the off ending machine across the counter. It turned out to be a Panasonic NV-G40, a very recent model featuring remote control and digital scanner, though I'm not quite sure what the scanner is supposed to scan; I have yet to see any published programs featuring the required bar pattern. But that point aside, I was a little concerned because this was the first model I had encountered at service level and I had little technical information on hand. Fortunately, I soon realised that this machine uses the same deck as many earlier models; right back to the model NV-G20 in fact. Later that day, when things were a bit slack, I decided to at least try the machine and clarify the exact nature of the fault. So I set it up on In this case the loading had not proceded far enough to leave a loop of tape outside the cassette but I imagine that it was a variation of this routine which had created a loop on at least one occasion when the customer used the machine. If the loading had proceded a little further before the cassette was rejected, this could well have happened. And in view of what I subsequently found, it is quite likely that the fault varied from time to time. But right now, I didn't have a clue and what I had seen didn't inspire me with a great deal of confidence. It conjured up visions of a faulty mode select switch or something equally complex in a machine with which I was only partly familiar. In any case, it looked like a job that would have to be put aside until I had more time. the bench and pushed in a cassette. Initially, all seemed well; the cassette carrier accepted the tape and, apparently, set it down on the deck. But then it rebelled and promptly unloaded the cassette. Well, that was a new one on me. Fortunately, this machine is very easy to get at; only four screws need be undone to release the cover and this reveals both the deck and the main printed board, which sit side by side. That done, I tried loading the cassette again. And now I could see that the process went as far as putting the cassette on the deck and starting the actual tape loading process. In this machine the loading process differs somewhat from the more usual arrangement. Instead of waiting for the "play" instruction before extracting the tape from the cassette and wrapping it around the drum, this machine begins extracting the tape as soon as the cassette reaches the deck. It doesn't go all the way. It extracts enough tape to allow it to be loaded against the audio/control head. The idea appears to be to provide better tape control during the subsequent loading process, though I have not worked out the details of this. Anyway, this was where the loading process baulked. It began this first stage but before it could complete it, the cassette was unloaded. Hairy legs So I contented myself with extracting the cassette from the carrier and giving the deck assembly a quick visual inspection. And that's when I saw it. It was on the deck, to the left of the supply reel disc, hard against the front of the machine and partly hidden by the cassette carrier assembly mounted above the deck. "It" was a very large tarantula spider and, initially, I wasn't sure whether it was dead or alive. This didn't worry me particularly as tarantulas are quite harmless. As it turned out he (or she) was very dead and I was able to fish him (or her) out without too much trouble. There were also a couple of spare legs lying around which I also recovered. Thus inspired I gave the rest of TETIA TV TIP Philips K9A Symptom: Grotesque north/sou!h distortion. Picture height normal 1n the centre of the.screen but reduced to almost nothing at the sides. Cure: Broken track between N/S adjust trimpot R602 and the N/S transductor. This break forces the whole vertical scan current through the transductor, instead of sharing it with the adjustment network. the deck a thorough inspection, removing the cover above the head drum in the process. This would have been done anyway, since I make it a policy to give all tape-path components a routine clean regardless of the main fault. I also wanted to make sure there were no more beasties involved. There weren't as it turned out but I was surprised at the condition of the head drum. The working face was reasonably clean, although there was some oxide build-up on the guides and auxiliary heads; rather more, in fact, than I expected in a new machine. But the real surprise was the amount of muck on the top of head drum. This took the form of a sticky coating and a pattern of spots; the latter, I assumed, being excreta from the now departed tarantula. Anyway, I cleaned everything up, including the oxide build-up, then put the machine through its paces again. And that was it; everything worked perfectly. I can only guess as to the exact manner in which the corpse was gumming up the works and I can't even be sure that it was exactly the same on my bench as it was in the customer's home (it may well have moved around in transit). It might have been fouling the brake mechanism and the machine sensed this fault and refused to accept the cassette for this reason. Another query concerns just how the monster got into the machine. Like most such devices, it is well enclosed but there are ventilation slots in several places, some of them a little wider than typical. And knowing just how small a space these creatures can negotiate, it wouldn't surprise me if this was the explanation. Alternatively, it is just possible that it gained entry via a cassette, there being two large pockets on the underside which could easily accommodate it. Technically, that was the end of the story. However, I had to inform the lady that the warranty did not cover the entry of tarantula spiders into the machine, so I would have to charge her. Fortunately, she accepted this philosophically. So what will we find next? -~ APRIL 1989 75