Subject: 7800 EPROM conversion From: btomlin@crl.com (Bruce Tomlin) Date: 18 May 1996 14:07:11 -0700 Parts needed: 74LS04 chip (No other 74x04 variants! I tried a 74F04 and it didn't work.) 28 pin IC socket EPROM chip, either 2732, 2764, or 27128 About 5 inches of wire wrapping wire, and a razor blade to help strip it Soldering iron, solder, desoldering iron, etc. 1) Desolder the old ROM chip. This is the one marked "CO24922". If you haven't desoldered chips before, get some practice or buy a pizza and split it with a friend who has. (See end of this file for tips on how to desolder an IC chip.) Also suck the solder out of the four extra holes. 2) Strip one end of the wire wrap wire and put it into the pin 22 hole. This is the one to the "right" of the letters "DBM". 3) Insert the 28 pin socket into the holes and solder it down, along with the wire wrap wire. Test your work by putting the ROM chip back in and plugging in a 7800 game. If the "ATARI" screen comes up and then the game starts, everything is okay. 4) If you are going to be using a 28 pin EPROM chip, suck the solder out of the holes marked "W1" and desolder the resistor-like thing from the adjacent holes (which are marked "W2"). It may look like a resistor, but if it is, it's zero ohms. Solder the resistor-thing into the W1 holes. 5) Take the 74LS04 chip and bend up all but the four "corner" pins (1, 7, 8, and 14). Piggyback it over the 74AHCT08 or 74LS08 chip which is just above the biggest chip on the board. Solder down pins 1, 7, and 14. Now bend up pin 8. 6) Strip off the other end of the wire wrap wire and wrap the end around pin 2 of the 74LS04. Before putting it on the 74LS04, thread it under some resistors and capacitors to keep things tidy. Solder the wire to the pin. 7) Find the trace on the bottom of the circuit board that goes between pin 1 of the 7408 and the ROM pin that you stuck the wire wrap wire into. There is a place next to the 7408 where you will have enough room to cut the trace safely. Cut it. 8) Program a 2732, 2764, or 27128 EPROM (or a 28xxx EEPROM if you prefer) with a copy of the 7800 ROM in the last 4K. 9) Put the ROM into the socket and test everything by plugging in a 7800 game. Now you're done! Hints for desoldering: * I use a Radio Shack desoldering iron. This has a red rubber bulb on it and a hollow tip. It's cheap and works well. * Use a fresh tip for important projects! It's not worth trying to save two bucks only to ruin a circuit board or a chip. Tinning your tip is a good idea, too. * Wait for the joint to completely melt before sucking out the solder. If you suck too soon, you may not be able to melt the joint properly any more. Wait about four seconds, or five for the four "corner" pins. * When you have sucked out the solder from all of the holes, push all the pins to "crack" them off of the remaining solder. * If you have done everything right, the chip should practically fall out of the board. 7800 ROM dump: BEGIN 644 BIOS7800.BIN M2&ST /______________________________________________________ M____________________________________________________________ M____________________________________________________________ M____________________________________________________________ M____________________________________________________________ M____________________________________________________________ M____________________________________________________________ M____________________________________________________________ M____________________________________________________________ M____________________________________________________________ M____________________________________________________________ M____________________________________________________________ M____________________________________________________________ M____________________________________________________________ M____________________________________________________________ M____________________________________________________________ M____________________________________________________________ M____________________________________________________________ M____________________________________________________________ M____________________________________________________________ M____________________________________________________________ M____________________________________________________________ M_____________________________________________TS")DS")JD6A0&@ M_Z)_O0#^V8#]T.J(RA#TK?S_+?W_R?_PW*W\_PW]__#4K?C_"?[)_]#.K?C_ M2? I\-#%K?G_*0O) ]"\K?G_*?"%[HT&),E D*[I - !JI *($G0 :G0 @ MHG>] "#= !K0!LH0]4RY)DS")J( ?0 8?0#_J+G5+9T &.C0\&"B #X &.C0 M^F (QO 0#*D"A0&E\##\J1:% 2A@QV6KRN[W@PGAT))G8K9R58Z1W,6!OG@@ M6;?F/09%K\@(,3C1^W.$J1?\-(>CE/J0N.W..UL*0]GS4X*S#6U:8)U1I[D1 M$+SD?X!!Y^/V5B8U[-;?#'_TGJQ21N_/OZ(_I!,5ETH8O8GYM7&?@J+78.Z"Y+^0<#WI,6?M3ELO!]>MK2H&Y+W5_IT!&,@X27&\J7@C7(EHG>] !B= "#*$/=@(#DFI.7( MA.&8&&7B2*JI (UQ)IT &,K0^HT &,B,;B:,=":,?":,@2:B ,YN)LYT)LY\ M)LZ!)L;A,!NDX;D (#W9)? )O6(FC7(F(&HFZ. (,.A,I"5HA>&I 87@8 $" M! @0($" (#DFI>,XY>2%X(7AH@". !B.CR:.K";*CJDFCHPFCI(FCIHFCI\F MH@?NJ2;NC";NDB;NFB;NGR;&X3 7O6(FC9 FC:TF(*8FD ,@B";*$.Q,"":E MXX7A8*;DZ(;BH ", !FY8B:-52;(N6(FC5DFIN(8O0 9*IT &'R&DXABY !AY !F9 !B($/20#+D %VD F0 7B$QY)F"DXCBY !CY M !F9 !B($/2P#+D %^D F0 7B$R7)F"@ +D &-D &? !8,3B\/O(3*@FHA:& M 9KX;/S_J0*% :)_O=3WG8 $RA#W3( $J0"JA0&5 ^C@*M#YA0*I!.HP(Z($ MRA#]FHT0 2#+!"#+!(41A1N%'(4/ZH4"J0#J, 0D S )J0*%"8T2\= >) (P M#*D"A0:-&/&-8/30#H4LJ0B%&R#+!.HD C#9J?V%"&S\_^K_____________ M____________________________________________________________ M_____________________ZD=A0%XV*D"A0&I^X7UJ1*%]*E_A3RI (4@H@6] M'?F@ )D (-D (- GF0 AV0 AT!^(T.W*$.6I0XV (,6 T N-@"'-@ '0 TPX M^: $3(#XC0 8S0 8T J@ 4R ^* "3(#XH -,@/BI (7PA?*@!X3TN2/YA?&Y M*_F%\Z(%O1WYH "1\-'PT-"1\M'RT,^(T/'*$.G&]*3T$-=,%_L _U6J:0\B M(R0E)BJ0Z##F MT.3I5;#@$-[PW,FKT-@8Z:J0TS#1T,^I_ZKHT#;*\#,0,>#_T"VHR- IB/ F MR- CA?#F\- =Q/#0&<;P\!7%\- 1J:H8*BHJR5+0!VIJ:LFJ\ -,,_D*D/H* ML/<*R5#0\DD%2I#M2K#J2LD*T.6I50D;R5_0W2E5*1O)$=#5"55)&\E.T,T@ MD?I,6/JZX%+0PFC)C="]:,GZT+BI^$BIYDA@3%CZBDBI0X4\H@^E[X4B)/-0 M!A "A22%)(4D..D0R1"P ND/A2+*$.RB0(8\*? )#H4GI>\I\ D&A24I\!AI M0) ":0\) X4FQO$0&:7S:6"0$:7O&&D0D )I#X7OI?*%\:D A?.I H7P:*IH M0$P4^Z+_FJD JI4!Z. 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