{"id":391,"date":"2015-08-08T14:37:00","date_gmt":"2015-08-08T14:37:00","guid":{"rendered":"http:\/\/machineryequipmentonline.com\/video-equipment\/uncategorized\/timebase-servicing\/"},"modified":"2015-08-08T14:37:00","modified_gmt":"2015-08-08T14:37:00","slug":"timebase-servicing","status":"publish","type":"post","link":"http:\/\/machineryequipmentonline.com\/video-equipment\/timebase-servicing\/","title":{"rendered":"TIMEBASE SERVICING"},"content":{"rendered":"<div class=\"qthwo6a0dbc7b46bb0\" ><script type=\"text\/javascript\">\n\tatOptions = {\n\t\t'key' : '61e5902552e2353963d8d2f1bd1f4a8f',\n\t\t'format' : 'iframe',\n\t\t'height' : 250,\n\t\t'width' : 300,\n\t\t'params' : {}\n\t};\n<\/script>\n<script type=\"text\/javascript\" src=\"\/\/www.highperformanceformat.com\/61e5902552e2353963d8d2f1bd1f4a8f\/invoke.js\"><\/script><\/div><style type=\"text\/css\">\r\n@media screen and (min-width: 1201px) {\r\n.qthwo6a0dbc7b46bb0 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 993px) and (max-width: 1200px) {\r\n.qthwo6a0dbc7b46bb0 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 769px) and (max-width: 992px) {\r\n.qthwo6a0dbc7b46bb0 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 768px) and (max-width: 768px) {\r\n.qthwo6a0dbc7b46bb0 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (max-width: 767px) {\r\n.qthwo6a0dbc7b46bb0 {\r\ndisplay: block;\r\n}\r\n}\r\n<\/style>\r\n<h5 align=\"justify\"><em><u>TIMEBASE SERVICING<\/u><\/em><\/h5>\n<p align=\"justify\">In \ufb01eld timebases where the fault is complete lack of output (single horizontal line across the screen) the \ufb01rst essential is to reduce screen brightness to prevent damage to the phosphor layer. Once it is established that the operating voltages for all sections of the time- base are present, the next step is to ascertain which section \u2013 oscillator, driver or output stage \u2013 has failed, for which the oscilloscope is the best tool. Where the entire timebase or ampli\ufb01er is embodied in a single IC which is proved faulty, check for destructive conditions before \ufb01tting and powering a new one. Typical of these are a shorted \ufb02yback diode (D305 in Fig. 10.3, D109 in Fig. 10.4), excessive sup- ply voltage, shorted capacitors or heavy output loading due to a leak- age or short-path to ground. <\/p>\n<p align=\"justify\">More often, \ufb01eld faults will take the form of various kinds of raster- shape distortion. Low supply voltage, faulty electrolytic capacitors or incorrect feedback conditions are the most common causes of these. A top foldover effect with teletext line superimposed is due to slow \ufb02yback. A cramping at picture bottom is generally due to an inability of the supply line or the output stage to furnish sufficient current to drive the scan coils fully; this may well be due to a dried-up or ageing electrolytic decoupling capacitor on the supply line to the \ufb01eld output stage. <\/p>\n<p align=\"justify\">Where the line oscillator, driver and output stages are not involved in the generation and control of power supplies (see Chapter 11) the diagnosis of a \u2018no-go\u2019 fault follows the same pattern of signal (here, pulse) tracing from oscillator via driver to output stage. Line oscillators and drivers are much more reliable than the output stage, which works with relatively heavy currents and high pulse voltages. A quiescent line output section is easy to troubleshoot with test-meter and oscilloscope \u2013 such things as dry joints, faulty base drive resistor or open base junction in the output transistor are usually responsible. <\/p><div class=\"uydga6a0dbc7b46d79\" ><script async src=\"https:\/\/pagead2.googlesyndication.com\/pagead\/js\/adsbygoogle.js?client=ca-pub-0778475562755157\"\n     crossorigin=\"anonymous\"><\/script>\n<!-- 300x600 television-and-video -->\n<ins class=\"adsbygoogle\"\n     style=\"display:inline-block;width:300px;height:600px\"\n     data-ad-client=\"ca-pub-0778475562755157\"\n     data-ad-slot=\"6549443290\"><\/ins>\n<script>\n     (adsbygoogle = window.adsbygoogle || []).push({});\n<\/script><\/div><style type=\"text\/css\">\r\n@media screen and (min-width: 1201px) {\r\n.uydga6a0dbc7b46d79 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 993px) and (max-width: 1200px) {\r\n.uydga6a0dbc7b46d79 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 769px) and (max-width: 992px) {\r\n.uydga6a0dbc7b46d79 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 768px) and (max-width: 768px) {\r\n.uydga6a0dbc7b46d79 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (max-width: 767px) {\r\n.uydga6a0dbc7b46d79 {\r\ndisplay: block;\r\n}\r\n}\r\n<\/style>\r\n<div class=\"dzhef6a0dbc7b46caa\" ><script type=\"text\/javascript\">\n\tatOptions = {\n\t\t'key' : '0c1eb4c533eaedb7b996f49a5a4983a9',\n\t\t'format' : 'iframe',\n\t\t'height' : 300,\n\t\t'width' : 160,\n\t\t'params' : {}\n\t};\n<\/script>\n<script type=\"text\/javascript\" src=\"\/\/www.highperformanceformat.com\/0c1eb4c533eaedb7b996f49a5a4983a9\/invoke.js\"><\/script><\/div><style type=\"text\/css\">\r\n@media screen and (min-width: 1201px) {\r\n.dzhef6a0dbc7b46caa {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 993px) and (max-width: 1200px) {\r\n.dzhef6a0dbc7b46caa {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 769px) and (max-width: 992px) {\r\n.dzhef6a0dbc7b46caa {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 768px) and (max-width: 768px) {\r\n.dzhef6a0dbc7b46caa {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (max-width: 767px) {\r\n.dzhef6a0dbc7b46caa {\r\ndisplay: block;\r\n}\r\n}\r\n<\/style>\r\n\n<p align=\"justify\">More often line output stage faults are manifest as excessive load- ing, leading to a high current drain on the power supply, which will usually invoke the latter\u2019s overcurrent protection system; the end result, then, will often be a \u2018pumping\u2019 symptom, as will be described in the next chapter. First the e.h.t. recti\ufb01er or multiplier (if external to the l.o.p.t.) should be disconnected from the overwind. If the set now bursts into life replace the e.h.t. recti\ufb01er. Should the stage still not function, the output transistor and efficiency (where relevant, E\u2212W modulator) diodes should now be checked for leakage. The can also be loaded by leakage in any other recti\ufb01er diodes it may feed, or by heavy loading of their outputs, e.g. a leaky or shorted A1 reservoir capacitor. If after exhaustive testing, and unloading of suspect components, the stage remains heavily loaded, the l.o.p.t. itself is suspect for short-circuit turns or (in diode-split types) faulty internal multiplier components. Shorting turns in the line scanning coils can give rise to similar symptoms, but this is rare; it can be checked by disconnecting the yoke. <\/p>\n<p align=\"justify\">During fault-\ufb01nding it is often prudent to work with reduced volt- ages and currents in the line output stage to prevent damage, and this can be arranged by \ufb01tting a suitably heavy wire-wound resistor in the h.t. feed line to the stage, or by feeding the set from a <i>v<\/i><i>ariac <\/i>\u2013 details in the next chapter.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>TIMEBASE SERVICING In \ufb01eld timebases where the fault is complete lack of output (single horizontal line across the screen) the \ufb01rst essential is to reduce screen brightness to prevent damage to the phosphor layer. Once it is established that the operating voltages for all sections of the time- base are present, the next step is [&hellip;]<br \/><a href=\"http:\/\/machineryequipmentonline.com\/video-equipment\/timebase-servicing\/\" class=\"more-link\" >Continue reading&#8230;<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[1],"tags":[],"aioseo_notices":[],"views":695,"_links":{"self":[{"href":"http:\/\/machineryequipmentonline.com\/video-equipment\/wp-json\/wp\/v2\/posts\/391"}],"collection":[{"href":"http:\/\/machineryequipmentonline.com\/video-equipment\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/machineryequipmentonline.com\/video-equipment\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/machineryequipmentonline.com\/video-equipment\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/machineryequipmentonline.com\/video-equipment\/wp-json\/wp\/v2\/comments?post=391"}],"version-history":[{"count":0,"href":"http:\/\/machineryequipmentonline.com\/video-equipment\/wp-json\/wp\/v2\/posts\/391\/revisions"}],"wp:attachment":[{"href":"http:\/\/machineryequipmentonline.com\/video-equipment\/wp-json\/wp\/v2\/media?parent=391"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/machineryequipmentonline.com\/video-equipment\/wp-json\/wp\/v2\/categories?post=391"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/machineryequipmentonline.com\/video-equipment\/wp-json\/wp\/v2\/tags?post=391"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}