.op Thió  filå  describeó  ALÌ thå modificationó foò  thå  Biç  Boarä developed by Trevor Marshall, SYSOP, Thousand Oaks Technical RBBS, 31364 Via Colinas, Westlake Village, CA 91362 phone (805) 492 5472 (24 hours) (many thanks to Steve Hope, who helped develop the video mods) ---> released 8/27/82 formatted for WORDSTAR Thå  doublå densitù modificationó requirå aî additionaì  hardwarå PC  whicè  plugó intï thå 177± socket®  Iô  containó  á  WD1791¬ WD1691¬  WD214³ anó 74S124® É havå passeä thå detailó oî tï MICRÏ CORNUCOPIA, the journal of the Big Board Users Group. --------------------------------------- ACHIEVING RELIABLE 5MHz OPERATION YOU WILL NEED A HIGH SPEED EPROM FOR YOUR PFM MONITOR. Thå  2716-1ó  distributeä bù DÒ worë fine¬  É useä thå  onå  theù supplieä  foò  thå characteò generator¬  whicè workó OË witè  anù 'Gardeî variety§ EPROM®  Ensurå yoõ prograí youò fasô PFÍ monitoò before attempting these mods. 1. Thå RAÍ arraù ió refresheä bù 12¸ RAÓ onlù cycles®  Thå delaù     needed to clock in the column data is provided by U76.     Tï  operatå aô 5MHÚ wå musô cuô thå trackó tï pinó ´ anä µ oæ     U76 and move the CAS line to pin 4 and the MUXC to pin 3.     The Z80 clock can then be changed from U96 pin 4 to pin 5.     Thå  clocë linå foò thå Z8° chipó haó tï bå dampeä aó  iô  ió     resonant and the consequent ringing causes problems.     Twï  3³  ohí  resistoró arå needed¬  onå iî serieó  witè  thå     collectoò  leaä oæ Q2¬  whicè musô bå changeä tï aî  MPS3640¬     anä onå iî serieó witè piî ¸ oæ U77¬ whicè musô bå changeä tï     á 74S04® Á 3K³ resistoò musô bå soldereä betweeî pinó ³ anä ·     of U77 to yield a more symmettrical 20MHz waveform.     Thå  tracë  tï piî ¸ oæ U7· ió cuô oî thå toð  oæ  thå  boarä     between U77 and U79.     Thå  3³  ohí resistoò ió soldereä betweeî U7· piî ¸  anä  thå     plated thru hole adjacent to pin 16 of U80. More formally, Cuô  tracå betweeî piî ´ oæ U9¶ anä piî ¹ oæ U7¸ oî bottoí oæ     board.     Link pin 5 of U96 to pin 9 of U78     Cuô  tracå  betweeî  piî µ oæ U7¶  anä  plateä  througè  holå     adjacent to pin 3 of U65     Link this plated thru hole to pin 4 of U76     Cuô  tracå  betweeî  piî  ´ oæ U7¶ anä  plateä  througè  holå     adjacent to pin 8 of U52     Link this hole to pin 3 of U76. LOWER CASE MODIFICATIONS YOÕ  WILÌ NEEÄ Á NE× DISPLAÙ EPROM¬  seå filå DISPPROM.B foò  á Šhex image for your prom programmer.    Remove link from pins 14 to 3 of U11     Cut trace to pin 4 of U11 below board     Linë piî ³ oæ U1± tï plateä througè holå adjacenô tï piî ¹ oæ     U21 (below board)     Link pin 4 of U11 to pin 11 of U9     Cut trace to pin 11 of U9 below board     Link pin 5 of U25 to pin 9 of U60     Link pin 8 of U22 to pin 19 of U73     Cuô  tracå oî bottoí oæ boarä froí piî 1¹ oæ  U73®  iô  comeó     through a plated through hole adjacent to pin 4 of U73     Cut trace to pin 11 of U9 between U9 and U10 on top of board     Cut trace to pin 12 of U10 between U10 and U11     Cuô tracå tï piî µ oæ U25® Iô emergeó betweeî pinó ¶ anä · oæ     U2³  anä  disappearó  betweeî piî ¸ anä ¹ oæ U2²  oî  toð  oæ     board.     Linë  piî · oæ U1± (earth© tï thå plateä througè holå oæ  thå     tracå whicè useä tï gï tï piî ´ oæ U11® iô ió adjacenô tï piî     13 of U22. IMPROVING THE VIDEO DISPLAY CIRCUITRY 1.  Improveä  compositå  videï waveformó resulô froí linkinç  TB±     piî ¶ tï piî 2® Á 56° ohí resistoò shoulä bå betweeî TB± pinó     ³ anä 4®  R2± shoulä bå reduceä tï 56° ohms®  C14² shoulä  bå     omitted. TB1 pins 10 and 11 should be jumpered.     R2 should change to 1200 from 820 ohms. CONVERTING THE FLOPPY DISK CIRCUITRY TO DOUBLE DENSITY 1. Cuô  tracå froí piî 1² oæ U11± oî toð oæ thå boarä beforå  iô     goeó  tï  thå plateä thrõ hole®  Thå softwarå  haó  beeî  re-     written so that the PBRDY handshake is not required. 2.  Cut trace from U102 pin 37 to U102 pin 22.     Linë  U10² piî 3· tï U11± piî 12®  Thió ió thå Doublå Densitù     control line. 3.  Linë U11± piî ¹ tï U11² piî 13® Linë U11² piî 1² tï piî 1´ oæ     J±  (thå floppù disë drivå header)®  Thió connectó  thå  Sidå     Select circuitry of the YEDATA drives. 4.  Cuô  thå  tracë  froí  U10² piî 2· oî thå toð  oæ  thå  boarä     betweeî U10² anä U10´ piî 6®  Linë U10² piî 2· tï U10± piî 3®     Thió  ió thå RA× DATÁ line¬  whicè musô bypasó  thå  on-boarä     circuitrù  wheî  usinç thå doublå  densitù  controller®  Wheî     changinç bacë tï thå 177± thió ió thå onlù linå whicè musô bå     repaired. Pin 37 may be left as modified. 5. Cuô  trë  froí U11² piî ± oî toð oæ boarä beforå  thå  plateä     thrõ hole® Connecô U11² piî ± tï U11± piî 13® Thå drivå poweò     signaì  ió no÷ deriveä directlù froí thå drivå selecô  enablå     line. (leaving pin 8 free for the CACHE memory bank select). ŠADDING THE EXTRA BANKS OF 64K RAM 1. Wå neeä tï disconnecô thå selecô lineó tï U53®  Firsô Isolatå     U5³  piî  1°  anä U5³ piî ´ bù cuttinç thå trackó  froí  theí     betweeî U5³ anä U54. Theî cuô thå trackó froí U5³ piî 1³ anä U5³ piî ± betweeî U5³     anä U54. 2. Thå multiplexeò tï drivå A· oæ thå 64Ë RAMó musô bå freed® Iô     ió currentlù useä aó á buffer®  Cuô tracë betweeî pinó 1° anä     1± oæ U5¹ underneatè thå boarä anä froí piî 1° oæ U5¹ betweeî     U5¹ anä U5¸ oî toð oæ board®  Cuô trë froí piî ¹ oæ U5¹  nexô     tï R13.     No÷  linë  thå 3³ ohí resistoò thaô waó connecteä tï piî  U5¹     piî ¹ tï thå plateä thrõ holå jusô belo÷ piî U5¶ piî 8® (Thió     holå useä tï leaä tï U5¹ piî 10® (Á buffeò ió noô required)® 3. Thå  64Ë  RAÍ chipó onlù requirå á +µ volô  supply®  Alì  thå     supplieó musô bå re-routed¬  anä thå olä +µ volô supplù lineó     no÷ becomå A7® Removå C1-C8® Cuô thå trackó froí eacè oæ C78-     C8µ  tï piî ¸ oæ eacè columî oæ thå RAÍ array®  Linë piî ¸ oæ     each column to the next (8 links or a daisy chain).     Connecô  U5¹  piî  ¹  tï U4¶ piî ¸ witè  á  3³  ohí  resistoò     (underneatè   thå  board)®   Connecô  A1µ  anä  A1´  tï   thå     multiplexeò bù linkinç U5¹ piî 1° tï U5µ piî ± anä U5¹ piî 1±     to U55 pin 2. 4. The +12 and -5 supplies to the RAM array must be cut.     Thå  ¸  trackó tï thå rowó oæ thå RAÍ arraù thaô  carrù  theí     musô bå cut.     Tï  bå  surå  thaô yoõ havå noô forgotteî anù iô ió  wiså  tï     shorô pinó ± anä ¸ oæ U1,U1³ anä U2¶ anä tï placå á 5Volô MOÓ     protectioî diodå typå MPT5Å (oò 5.6Ö 5Watô zeneò iæ MPT5Å noô     available© betweeî pinó 1¶ anä ¸ oæ anù onå oæ thå RAMs. 5. Thå  ne÷  +µ  volô supplù caî convenientlù  bå  connecteä  bù     solderinç  aî RÆ chokå (¶ holå type© betweeî piî ¸ oæ U3¹ anä     the +5 rail adjacent to U53. 6.  Extrá  BANË  SELECÔ  gatinç musô no÷ bå  provided®  Aî  extrá     74LS1° ió addeä tï thå boarä betweeî U¸ anä U¹ tï providå thå     additionaì functions¬  howeveò iæ twï extrá bankó oæ 48Ë  arå     desireä  theî  U1° pinó 2,1,1³ musô bå freeä foò uså  bù  thå     banë selecô circuitry.     Piî  ²  passeó undeò Ià towardó U11®  Cuô iô betweeî thå  twï     ICs®  Thå  piî  1² tracë shoulä alreadù havå  beeî  cut®  Cuô     tracks to pins 1 and 13 on the underside of the board.     The 74LS10 alone can handle the cache memory. .pa ŠThe selection process is this:     BANË 0¬ thå maiî memorù banë ió enableä wheneveò anù oæ thå ´     outputó  oæ  U5µ arå activå (low© anä alì oæ BANKÓ 1,² anä  ³     are not active.     BANË 1¬  thå disë CACHÅ memory¬ ió enableä wheî piî ¸ oæ U11±     ió  activå (LOW)®  Aô power-oî PA¶ floató (HI© anä BANË ±  ió     thus disabled.     BANË 2¬  thå sparå memory¬ ió enableä bù sacrificinç thå BELÌ     (oî  PA4)®  Iô  ió  enableä iæ thå  appropriatå  jumperó  arå     installeä  anä PA´ ió LOW®  THESÅ JUMPERÓ MUSÔ NOÔ BÅ ENABLEÄ     IÆ THÅ BELÌ IÓ TÏ BÅ USED® Á SPECIAÌ VERSIOÎ OÆ THÅ OPERATINÇ     SYSTEÍ IÓ REQUIRED. ---¾  Thå  filå BBSYSTEM.ZQ° ió thå BIOÓ É uså foò CP/Í  anä  thå monitor ROM ---¾  Thå filå BBDRIVER.ZQ° ió thå CACHÅ buffeò BIOó É developeä for INFOSOFT IOS v2.34 ICs WHICH SHOULD BE PURCHASED WITH CARE     U75 should be 74151     U77 must be 74S04 SHOTTKY TTL     U76 should be 74164     U59 and U58 must be 74157     U112 should be 7414 to drive the floppy disk signals     U109 should be 7445 for the same reason     Alì  Z8°  chipó  shoulä bå Z80  types¬  althougè  onlù  Z80Á     CTC,SIÏ  anä PIÏ arå currentlù available®  Theù seeí tï  worë     well, as does standard 250 nsec memory. ...............Trevor Marshall, last revision 27 Aug 82.  .