[time-nuts] Fixing an HP 5370A with a missing ROM board

Fri Jul 24 20:22:07 UTC 2009

Mark,

While I don't have a need for your mod, I wanted 
to congratulate you on some "First Class" thinking.

Had
K7MLR

At 09:50 AM 7/24/2009, you wrote:

>I recently got in an HP5370A that had been 
>robbed of the ROM card and the oven oscillator 
>power supply card...  ah, crap...  Swapping the 
>missing cards from a known good unit showed the 
>counter was in otherwise excellent operating condition.
>
>The HP5370A firmware is stored on eight 2708 
>1Kx8 EPROM chips on the ROM card.  The firmware 
>is compiled to execute at addresses 
>7800-7FFF.  The system normally does not use 
>address line A15 and the upper and lower halves 
>of the address space are mirrored.  (BTW,  the 
>system address bus is inverted 
>polarity...  important to remember if you are looking at the code).
>
>It turns out that the 5370A CPU card has an 
>empty socket for a firmware ROM.  This socket 
>supports a 4Kx8 ROM that will appear in the 
>address space at C000-FFFF if switch 3 on the 
>CPU card is turned on.  Hmmm,  with a little 
>modification it should be possible to install an 
>8Kx8 EPROM there with a copy of the firmware.
>
>Motorola did make the MCM68764 and MCM68766 8kx8 
>EPROMS in a 24 pin package.  They are hard to 
>find (but are on Ebay for 4 bucks each) and most 
>programmers do not support them.  The EPROM A12 
>address line is on a pin tied to +5V on the CPU 
>board socket (pin 21).  You could easily patch 
>the board and use the Motorola chip.
>
>I have a pile of 27C512 (64Kx8) EPROMS in a 28 
>pin DIP package.   Most of the pins match the 
>CPU board ROM socket connections so I chose to 
>use them.  To use the 27C512 chip,  first I read 
>in each of the eight 2708 chips from a good 
>5370A ROM board using a Data I/O Unisite 
>programmer (note that the DIO 2900 and 3900 
>series programmers don't support 
>2708's!!!).  Next I used the DOS COPY command to 
>concatenate the 8 1Kx8 ROM images into a single 
>8Kx8 ROM image file (remember to use the /B binary file parameter!):
>    COPY ROM1/B+ROM2/B+ROM3/B+ROM4/B+ROM5/B+ROM6/B+ROM7/B+ROM8/B  IMAGE.ROM/B
>
>Finally,  I concatenated 8 copies of the 8Kx8 
>image into a 64Kx8 ROM image which I then 
>programmed into the 27C512.  You could just put 
>one copy of the 8K ROM image into the upper 8K 
>of the EPROM,  but this was easier to do.
>
>Lift pins 23 (A11) and 20 (/OE) on the 27C512 so 
>that they won't go into the EPROM 
>socket.  Solder a jumper wire between EPROM pins 
>20 (/OE) and 22 (/CS).  Be careful not to short 
>to pin 21.  This connects the /CS and /OE pins 
>of the EPROM.  Solder a jumper wire between 
>EPROM pins  1,28,27,26.  This puts +5V on these 
>pins (A13,A14,A15,VCC).  Install the EPROM in 
>the CPU board socket.  Pins 1,2,27, and 28 of 
>the EPROM chip should be hanging in the air.
>
>Solder a jumper wire between pin 23 of the EPROM 
>chip (A11) and U14-7 on the CPU board (on the 
>photo,  I ran this wire to the back of the board 
>and picked up the signal on pin 18 of the 24 pin 
>the EPROM socket)  Solder another jumper wire 
>between pin 2 of the EPROM chip (A12) and U16-9 
>on the CPU board.  This connects the CPU address 
>bus A11 and A12 signals to the EPROM.  (you 
>should first verify that the CPU board pin 
>numbers mentioned match the revision/layout of your CPU board)
>
>Next,  you have to modify the CPU board to 
>properly address the new EPROM chip.  Cut pin 3 
>of U6 on the CPU board flush with the 
>board,  lift the nub of the pin up so it no 
>longer touches the board (this pin normally 
>connects to A15).  Solder a jumper to the lifted 
>pin and pin U16-11 (A13) on the CPU board.  This 
>modifies the CPU board so that the CPU external 
>data bus buffer will be disabled and the EPROM 
>chip will be enabled when the external ROM board 
>address space is addressed (i.e. A13 and A14 
>high instead of A15 and A14 high).
>
>Turn on DIP switch 3 on the CPU board to enable 
>the EPROM socket.  If all goes well,  you should 
>have a 5370A working without the ROM board (just like the 5370B does).
>
>_________________________________________________________________
>Windows Live™ Hotmail®: Celebrate the moment 
>with your favorite sports pics. Check it out.
>http://www.windowslive.com/Online/Hotmail/Campaign/QuickAdd?ocid=TXT_TAGLM_WL_QA_HM_sports_photos_072009&cat=sports
>
>_______________________________________________
>time-nuts mailing list -- time-nuts at febo.com
>To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>and follow the instructions there.