These 314 png sheets were scanned in at 600dpi from the original HP 3456A manual, and special care was taken to preserve the halftones. ---------------------------------------------------------------- THE INFORMATION BELOW PERTAINS TO THE FIRMWARE ROMS IN THE 3456A ---------------------------------------------------------------- The three MK36XXX ROMS in this meter are 24 pin 8Kx8 mask ROMs. They have been known to die or become corrupted due to old age. This used to be a common pinout. Equivalents are Signetics 2664, AMI S68364, Harris HM6388, NS DM87S228, NS DM77S228. These ROMS can be read on an EPROM programmer as the pin compatible Motorola MCM68766C35 aka MC68766 prototyping EPROM, as long as the reader is smart enough to strobes CS or OE when reading each address. Meters with serial numbers HIGHER-THAN 2015A03070 contain a NEWER ROM revision having the following part numbers and checksums: U5=1818-1629(C9CF5) U7=1818-1630(CD212) U8=1818-1631(D4CE2) Notice that the newer ROMS are certified to work in older meters. --------------- The ROMS can be directly replaced with pin-compatible EPROM MC68766 or MCM68766 but these are obsolete though easily available as surplus parts for about 10 dollars each. The SCM90448C might also be a direct replacement. Your EPROMS should have the following checksums: U5=(C9CF5) U7=(CD212) U8=(D4CE2) The procedure above is verified to work without any problems. Modern EPROMs type 27HC641 aka M27HC641 should also work and are pin compatible, as long as you cook the data a before burning, because A10 and A12 pins (if I remember correctly) are swapped. --------------- The data from each mask ROM can be split into two ordinary 2532 type EPROMs which are easily available. You just need to solder in the 3 missing ROM sockets and change the jumpers at the chip select logic on PCB A4 as follows. Remove jumpers: 2-3, 4-5, 7-8 and install the following new jumpers instead: 1-2, 5-6,8-9, 4-7. Split the original ROM from socket U5 across sockets U1 and U2. Split the original ROM from socket U7 across sockets U4 and U5. Split the original ROM from socket U8 across sockets U7 and U8. The checksums for the six split ROMS will turn out as follows: U1=(65C3C) U2=(640B9) U4=(6581A) U5=(679F8) U7=(6DBED) U8=(670F5) The procedure above is verified to work without any problems. --------------- To replace these ROMS with ordinary 2764 EPROMs you will need to make a socket adapter with the following pin connection changes. This is very easy if you use a wire-wrap socket having long pins. EPROM-Vpp-pin1 connects to +5V EPROM-PGM-pin27 connects to +5V EPROM-VCC-pin28 connects to +5V EPROM-/CE-pin20 connects to GND EPROM-/OE-pin22 connects to ROM-/CE-pin20 EPROM-A11-pin23 connects to ROM-A11-pin18 EPROM-A12-pin2 connects to ROM-A12-pin21 To replace these ROMS with ordinary 2564 EPROMs you will need to make a socket adapter with the following pin connection changes. This is very easy if you use a wire-wrap socket having long pins. EPROM-Vpp-pin1 connects to +5V EPROM-/CS1-pin2 connects to GND EPROM-/CS2-pin27 connects to GND EPROM-VCC-pin28 connects to +5V 2764 2564 +----o----+ MK36xxx +----o----+ 1 |Vpp Vcc| 28 2364 Vpp | 1 28| Vcc 2 |A12 /pgm| 27 +----o----+ /CS1 | 2 27| /CS2 3 |A7 nc| 26 A7 | 1 24| Vcc A7 | 3 26| Vcc 4 |A6 A8| 25 A6 | 2 23| A8 A6 | 4 25| A8 5 |A5 A9| 24 A5 | 3 22| A9 A5 | 5 24| A9 6 |A4 A11| 23 A4 | 4 21| A12 A4 | 6 23| A12 7 |A3 /OE| 22 A3 | 5 20| /CS A3 | 7 22| PD/PGM 8 |A2 A10| 21 A2 | 6 19| A10 A2 | 8 21| A10 9 |A1 /CE| 20 A1 | 7 18| A11 A1 | 9 20| A11 10 |A0 D7| 19 A0 | 8 17| D7 A0 |10 19| D8 11 |D0 D6| 18 D0 | 9 16| D6 D1 |11 18| D7 12 |D1 D5| 17 D1 |10 15| D5 D2 |12 17| D6 13 |D2 D4| 16 D2 |11 14| D4 D3 |13 16| D5 14 |Vss D3| 15 Vss |12 13| D3 Vss |14 15| D4 +---------+ +---------+ +---------+ Your EPROMS should have the following checksums: U5=(C9CF5) U7=(CD212) U8=(D4CE2). The procedure above is verified to work without any problems but is a bit messy and time consuming. --------------- The data from the three original ROMS can probably also be packed into a single 27256 EPROM but a socket adapter must be made, and a couple of address lines from the chip select logic must be tied to the EPROM. --------------- If replacing the ROMS does not work then try a new CPU: MC68A00P or HD468A00P which runs at 1.5MHz --------------- The 8048 MCU on PCB A30 in the meter is a mask ROM part which can be read on many EPROM programmers as an Intel 8748 MPU. You can then burn the image into an Intel C8748 EPROM MCU part. The checksum for a good 8048 binary ROM image is 1C936. The procedure above is verified to work without any problems. ...Stepan