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Type "0F" and check pins 9, 10, 15 and 16 of U6, they should all be at logic 1. Now type "00" and they should all be at logic 0. Typing "05" should give 0101 and "0A" should give 1010. Now repeat the above, replacing the first character with a "1" and checking the levels on U7, then "2" and U8, and finally "3" and U9.

Now type "00", "10", "30" then "70". After you typed the "70" the screen should show "00", the others should have given "**". The "Program" (red) LED should also be on. This set "00" on the data bus, selected write mode to enable U10, then read the data back down the RS232 link. The most likely cause of problems here is the RS232 link again.

Now type "31" then "70". The screen should show "FF" and the "Read" (yellow) LED should be on. U10 is now disabled so it's outputs are tristate and pulled up by RN1.

Typing "30" then "70" should return "00" again. Typing "0F", "1F" then "70" should return "FF", typing "05", "15" then "70" should give "55", and typing "0A", "1A" then "70" should give "AA". Also check that the appropriate data is actually reaching the EPROM socket pins as shown below:

Data Line	D7	D6	D5	D4	D3	D2	D1	D0
Socket Pin	19	18	17	16	15	13	12	11
Type	Expected Logic Level
"00", "10"	0	0	0	0	0	0	0	0
"05", "15"	0	1	0	1	0	1	0	1
"0A", "1A"	1	0	1	0	1	0	1	0
"0F", "1F"	1	1	1	1	1	1	1	1

 

Now we come to the address bus. Type in the program given in Listing 2 (save the other program first as it will be needed again). The program configures the programmer for 27512 EPROM's so all 16 address lines are bought to the EPROM socket and should be checked there. The program clears the address counter and then repeatedly increments the count, pausing at selected points to enable the checks to be made (see Table).

The logic levels should be checked on the pins of the EPROM socket when the program pauses, if a level is incorrect check on the appropriate pin on U11 or U12, then trace the fault as necessary. Note that the program may run quite slowly. A complied version (TEST2.EXE) which runs considerably faster is on the disk available from the author.

Now re-load the first test program. Connect a 'scope or logic probe to U15 pin 11. Type "30". Now when you type "60" you should observe a 40 millisecond positive going pulse. Move the probe to pin 8 of U15 and the pulse should be negative going. Now type "32" and repeat the above checks, the pulse should now be 1 millisecond. With a logic probe you will probably only be able to detect the presence of the pulse and will have to assume it is the correct length, with a test meter you probably won't be able to see anything!

Now switch off and insert U19. Connect a test meter set to about 500mA DC in line with the power input and switch back on. If the current is more than 100mA greater than it was before switch off and find out why! The most likely cause is a short circuit on VPP somewhere. If all is well remove the meter and connect the power directly. Set all four presets to the centre position.

Set a test meter to the 10V DC range and connect between pins 28 (+ve) and 14 (-ve) of the EPROM socket. Type "23" then "38", the meter should read 5V +/-0.25V. Now type "30" and the reading should rise, adjust RV1 for a reading of 6.1V +/-0.1V. Type "80" and the voltage should drop to zero. Set the meter to the 30V DC range and transfer the +ve meter probe to pin 1 of the EPROM socket. Type "34" and then adjust RV2 for a reading of 12.6V +/-0.1V. Type "30" and adjust RV3 for 21V +/-0.25V. Type "2F" and adjust RV4 for 25V +/-0.25V. Type "31" and the voltage should drop to zero.

The only thing left to check now is the various configurations for the different types of EPROM's. As described in "How it Works", the functions of six of the EPROM socket pins vary depending upon the type of EPROM. The address lines have already been checked at the EPROM socket, as has the programming voltage to pin 1. The checking of the remaining combinations is detailed below.