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SERVICEMAN'S LOG ' ''Bar humbug'' - as Scrooge G) <at> <at> <at> Transmit Button Bar Code Reader Display contained, hand-held device, the business end of which contains a sensor unit consisting of a LED and a photo transistor. The body of the device carries a liquid crystal display and a couple of switches and there is also an infrared LED at the far end of the unit (see Fig.1). The scanner is held vertically above the bar code pattern, in contact with the page, and moved smoothly across it. If done correctly this will store the information in the scanner and present it on the liquid crystal display panel for checking. The scanner will also beep to confirm that the code has been read completely. The display shows the day, starting time, finishing time and channel (see Fig.2). Ideally the bar code would be published as part of TV program guides but as mentioned last month guide publishers have been slow t~ respond. Possibly because of this, the VCR makers include a set of stock bar codes in the instruction manual. While this may not be as convenient to use, it certainly overcomes the lack of published data. Having fed the information into the scanner and checked it, the user then points the rear end of the scanner towards the , VCR and presses the transmit button. This transfers the data to the VCR via an infrared beam. The VCR confirms that the message has been received and understood by saying "Roger". Well, sorry about that, it doesn't really. No - most VCRs give an audible beep and present the scanner reading on the VCR display. But I offer the "Roger" idea to the manufacturers for what it's worth - no charge! <at> Transmitting Section The problem -- OK, so Scrooge never serviced a VCR. But if he had I imagine he would have used that expression in more than its original sense, because there is a certain amount of "bar" humbug around at the moment. What's this leading up to? - well, we're going to dig a little deeper into one of the bar (bah) code systems mentioned briefly last month. I have two stories concerning the National Panasonic model NV-D48 VCR and one of them deals with bar coding problems. This is the first time I have encountered any of the bar coding systems at service level. I've read about them, seen them demonstrated and played with them - but I have never had to service one. The most generous explanation for this would be that they are inherently reliable devices and this may well be so. But I think there is another factor - the "up-market" factor - which also has a lot to do with it. Although these systems have 4 been available for some two years now, their price tags have limited sales quite severely. One of my retailer colleagues tells me that he would have sold only about four such types in the last 12 months, compared with over 100 of the more conventional variety. Anyway, whatever the reason, this was the first time I had to put theory into practice. And it occurred to me that many of my readers may also have lacked the opportunity to gain hands-on experience with these devices. A brief run-down on how they are used may therefore be in order. The bar code scanner is a self- Bar Code Reading Section Digital Scanner On/Off Switch Fig.1: simplified diagram of the Panasonic bar coder with the essential features identified. Data is transferred to the VCR via an infrared beam. 50 SILICON CHIP would say Now for the specific problem. The customer rang to say that he had a National bar-code type VCR which he had bought about nine 1 V"~~~flrl -~::t~t~~~ C ~~,'fir/~·. f -:3 SOROOGE: Ft:><E:.'S -n-tE:. Ft'R.'SI ~ CO'D~.,oo months previously (ie, it was still under warranty). Apparently the bar coder had worked well until recently but was now behaving erratically. Sometimes it would record the information correctly but at other times it would baulk, either recording only part of the code or failing to record anything. There wasn't much I could do over the phone but I did establish that, when the scanner did load correctly, there was no problem in transferring the data to the VCR. In short, the problem appeared to be confined to the scanner so I suggested he bring it in, along with the instruction manual and the stock bar codes. He turned up a couple of days later and from the instruction manual I established that it was the model NV-D48; a model for which I had a service manual. A quick demonstration by the customer confirmed the symptoms so I suggested he leave it with me until I had time to delve deeper. When I finally addressed the problem I went through the same ritual as the customer - and came up with the same result; at best some of the code would be recorded, at worst nothing. My next move was to study the instruction manual in detail. As far as I could determine I was doing all the right things but one point did emerge. The instructions were quite emphatic about the need to clean the opening at the tip of the scanner, in front of the sensor, to remove any fibres picked up froni the bar-code paper. They even provide a small cleaning brush. My immediate reaction was to query whether the customer had followed this routine and I took the trouble to phone him and raise the point. He was quite adamant - he had cleaned the unit regularly, particularly after it had started to misbehave. Nevertheless, I went through the cleaning routine myself but without result - the thing was as cranky as ever. I tried again - still no joy. So I had to admit defeat and ask for help. I rang the National service department and contacted one of the technicians whom I know particularly well. Having listened to my story his first question was: "Have you cleaned the sensor opening?'' When I assured him that I had · several times - he was somewhat taken aback. As far as he could recall, there had been no electronic problems with these units so he was not able to suggest any approach. More to the point, if it was an electronic fault it was likely to be a nasty one; something not lending itself to field service. He was anxious to see it and suggested that I send it in to him. That was fine by me and I had it in the post in short order. And in due course it was returned, in full working order, and repaired nocharge under warranty. But in the manner of many service departments, there was no indication as to the nature of the fault, or what had been done. This is a most frustrating situation and one which the organisations concerned could well investigate. How do they expect their agents in the field to provide the best possible service without adequate feedback? After all, experience is the name of the game. Cat with cream Fortunately, I was due to meet the technician at a semi-social level within a few days, so I bided my time. When I did catch up with him, he smirked like the cat that had swallowed the cream. "Oh, there was nothing really wrong with it" . "What do you mean - if there was nothing really wrong with it, what was wrong with it? Come clean". "Well, the sensor unit was all fouled up with paper fibres and it needed cleaning properly". That was a bit of a blow. "Now wait a minute", I replied. "Come clean again. The customer had cleaned it several times and I cleaned it several times. And you say you cleaned it and it came good. What gives?" And that's when he stopped smirking and gave me the full story. It appears that the brush cleaning technique wasn't really good enough (more on that in a moment) and it was necessary to dismantle the device, remove the board and withdraw the sensor unit from the tunnel in which it sits, then thoroughly clean the face of the sensor unit. (The face of the sensor unit is set back from the opening by some 2-3mm). That's all very interesting from a servicing point of view but it does E) SU M© TU WE TH FR SA ON I ' ,_,c,c, ,_, D '-':,c,.c,c, ,_, .u ,_, OFF -, ,-, .,-, ,:,c,.c,: 0 Date Display e Start Time Display E) End Time Display 0 0 Channel Display Check Indicator Fig.2: this is what the display on the Panasonic bar coder looks like. Other makes and models would be similar. OCT0BER1989 51 SERVICEMAN'S LOG -CTD raise a question about the basic design. Although nobody is saying very much, reading between the lines I get the impression that this is now an acknowledged problem. But what the answer is I'm not sure. However, there are some additional points to consider. On the one hand the customer is a prolific user of the scanner; he would use it at least once every day. On the other hand the paper on which his bar codes are printed is a fairly good quality semi-gloss art paper which should not shed many fibres. So what happens if a similarly prolific user has access to codes printed on common newsprint? I shudder to think. At the very least I feel that a better cleaning brush or cleaning technique is required. Hopefully, something may eventuate. In the meantime, be prepared to do a thorough cleaning job. The next job As noted earlier, my next story also concerns an NV-D48 VCR. But there the similarity ends because it had a completely different fault. However, it did provide an opportunity to study some of the "digital" features more closely and learn something about their appeal. This machine was brought in by a lady customer, who simply turned up at the shop with it and a tale of woe,. The machine was quite new similar to the previous one - and therefore still under warranty. And the lady's complaint was that there were three or four white bars across the screen whenever she tried to play a tape on it. As well, a tape recorded on it would exhibit similar symptoms when played on another machine. It wasn't convenient to try the machine while the lady was there and in any case, my impression was that her description was quite accurate. So I said, "Leave it with me." When I did get around to checking it, I found that the lady's description was in fact very accurate. It was also rather disturbing because I hadn't seen anything as bad as this before. There were three or four noise bars, about 12mm wide, across the picture, similar to the single noise bar sometimes caused by a minor tracking error but far worse. The first thing I tried, without much conviction, was the user's tracking control, just in case it might provide a hint. It had no effect whatever - which probably meant something but I wasn't sure what. Bur WHEN ·11-\\S -PA"tr6-'RN CAN\E:. UP \"\ W~-S L-\KE:. NOT'\-\\NG 1 ~t> ~'R 'SE.E-N ~ ~ 0 1 • 52 SILICON CHIP Upper Cylinder Remover Jig (VFK0341) Handle LJ \. Soldered Portions Fig.3: this diagram shows the upper and bottom cylinders of the Panasonic drum assembly (separated for clarity), as well as the puller used to remove the upper cylinder. I then pulled the machine apart to the point where I could view the drum and transport system, while leaving it in playable condition. My first move was to check for any signs of oxide fouling. In fact, it was virtually spotless as I would have expected in such a new machine. Nevertheless, I went through the motions of giving it a thorough clean just in case but I wasn't really surprised when that achieved nothing. So where to next? I decided to set up the CRO and examine the output from the video heads in the playback mode (this procedure was covered in some detail in my April notes). In this case, test point TP3001 on the main board provides the RF output from the heads, following the head amplifier, and test point TP2001 provides the switching pulses to lock the timebase. The resultant CRO pattern from · this setup, using a standard test tape, should be a series of rectangular blocks which run together almost indistinguishably. Any suggestion of a triangular shape indicates a tracking error. But when this pattern came up it was like nothing I had ever seen before, either in real life or in the text books. It was not simply a mat- ter of each block being triangular; each block had three or four triangles in it. And, at the same time, the waveform amplitude was substantially reduced. Initial checks But what would cause such a gross tracking error? Or was it something more subtle? In desperation I decided to attack the left and right guide posts which are normally used to adjust the tracking. I shifted each guide post adjusting screw by half a turn, being very careful to note the original setting so that I could return to it. This had absolutely no effect one way or the other, which in itself seemed surprising. I was rapidly running out of ideas by now. Since it didn't seem to be a tracking error, at least in the conventional sense, the only possibility I could think of was a head problem of some kind. It was a long shot but it could not be ignored. One way of testing heads for wear is to use a head tester. This is a device which measures the "Q" of the windings and presents the result on an arbitary scale running from five on tlie left, to zero, then into a red area on the right. Five indicates a perfect head, anything between one and zero is poor, and anything into the red has really had it (my model is a Telesonic TE225). The major advantage of this approach is that the heads can be tested in-situ, the only requirement being to disconnect the lead to one side of each winding - four in this case - which is simple enough. So this was done - and produced exactly what I would expect from a near-new machine; "fives" all round. So that was that. I was really scratching now and the only thing I could think of was to unsolder the remaining four head drum connections and remove it for a more detailed examination, though I had no idea what I expected to find. Removing a head drum can be almost impossibly difficult or quite easy, depending on how one goes about it. You can try pulling it off with your fingers, which can be tough on both the fingers and the drum or heads. depending on how - . . I • t . f-~- . / t·. ~· ~ --•3 ff3 ~ ' ;;;[~/ . ... ( 3 ~ \ I ONE. w~'-t Ol= -rE:'Si\NG ~t>S ~ \,JEAR \6 "'t"'O use:. ~ \-\eA'O 1"E:-S"$1< lucky you are. Or you can do it properly, using a puller which is made for the job. It's really just a scaled down and refined version of an automotive wheel puller [see Fig.3). So I pulled the drum and gave it the best possible visual examination I could, even though such a check is of limited value. And, in fact, I found nothing about it to make me suspicious. But I did find something else. A complete drum assembly consists of two drums: a rotating portion which carries the heads [the upper cylinder) and a fixed drum, or bottom cylinder, which sits beneath it. This latter serves to guide the tape off the upper cylinder while holding it accurately TETIA TV TIPS Sony KV1300AS Symptom: Erratic horizontal sync, even with horizontal hold adjustment turned hard on. Picture usually out of sync at switch on but pulls in after a minute or two. Resulting picture is out of centre with wavy edges. Cure: C523 (1 00µF 25V electro) unserviceable. The cap showed no leakage and normal capacitance but would not work in this circuit. The cap is a filter on the main 18V rail but its failure only showed up on the horizontal sync. AWA-Thorn VCR ATV4 Symptom: All functions normal except that when Forward Speed Search is released the capstan motor speeds up instead of slow- ing down. Sounds as though it's going into orbit! Full servo alignment will correct this fault but introduces another - very slow recovery from Forward Speed Search with the sound unmuted. Cure: Adjust "speed search circuit" with VR408 and VR409, as per item 2-8 on manual page 24. This adjustment is a vital part of servo alignment but in the manual it's separated by 1 0 pages from those fnstructions and is often overlooked. TETIA TV Tip is supplied by the Tasmanian branch of The Electronic Technicians' Institute of Australia. Contact Jim Lawler, 16 Adina St, Geilston Bay, Tasmania 7015. OCT0BER1989 53 its location was such that the tape would have been approximately half on the upper cylinder and half on the bottom one. And the gunk would have been lifting the tape clear of the upper cylinder and the heads at that point. It may also have allowed the tape to move up and down slightly. But what was this gunk, and where did it come from? I'm afraid I can only guess. Although I recovered it, it was so small that its composition was impossible to determine, short of a well equipped laboratory. For what it's worth, my impression is that it was some kind of bituminous material. When the lady came to collect the machine I quizzed her as to the brands of tapes she used. I wasn't really surprised to learn that she used only the top brands; no el cheapos for her. Nevertheless, I feel that a tape is the most likely source of the gunk. Maybe it was one chance in a million whereby a good tape became contaminated, but that seems the most likely explanation. There was only one mildly sour note about the whole thing; the fault, not being inherent in the machine, was not covered by warranty. But the lady didn't quibble; she was happy enough to see the machine working again. SERVICEMAN'S LOG -CTD in position. It is formed with channels or " lands" in which the tape sits. And now that I had removed the upper cylinder I had a better view of the front of the lower cylinder, which is otherwise difficult to see because of its proximity to the cassette carrier. Using a large "reading glass" type of magnifier I was able to to give this section a much better examination. And that's when I saw it; a tiny black speck on the land area, at the top of the cylinder, directly in front of the cassette carrier. Once having seen it I was able to juggle a jeweller's loupe into the available space and get a rather better look at it. It was truly black, not at all like oxide, and appeared to be about half the size of a pin's head. And it wasn't just discolouration; it was a solid raised lump. I tried to remove it using a cotton bud but it wouldn't budge. Then I tried an alcohol soaked tissue around the end of my finger and even this didn't move it the first time. But it came away at the second attempt, leaving a faint dark stain behind. This was cleaned away with a few more wipes of the tissue. What was it? So, was that it? It seemed to be stretching things to blame such a gross fault on such a tiny particle but there was only one way to find out. I replaced the drum, resoldered the connections, and ran the tape again. And up came an almost perfect picture. By that I mean it was visually perfect, although the CRO pattern indicated a marginal tracking error. This responded to a very small adjustment of the guides and was, I imagine, an aftermath of my previous adjustments. And yes, that was it; all that trauma was caused by a near invisible speck of gunk. I'm not certain as to the exact mechanism by which it caused the effect it did but The thirst for knowledge / 1m, 'J: "D\SC.'f<~E:"i""L-Y ~,zze:-p "11-\~ t..A'D'-f A'BOV'r' 1lHS A'SPE:°' O F 11-1 ~ (V'\ACH IN e:..,u~.... 54 SILICON CHIP On a broader note, seeking to add to my knowledge of bar coders and how useful they are, I discreetly quizzed the lady about this aspect of the machine. Alas for my attempted survey; it appeared that she had hardly used this facility. The reason she and her husband had selected this machine was because they also owned a video camera and had a need for good editing facilities. Apparently the picture-in-picture, the various search facilities and the indexing system were just what they needed to provide precise and convenient editing. Warming to the subject, she went into this is some detail but I have to admit she lost me half way; she was much better informed about this aspect of the machine than I. I shall have to try to catch up. ~