Bulletin: SA0150 Subject: Upgrade PK-87 To PK-88 The first step is to discover which version of the PK-87 you have, the difference lies in the crystal used in the clock oscillator. The old version has a 2.4576MHz crystal while the newer version has a 4.9152 MHz crystal. Items required :- 32k static RAM low power (e.g.HN62256LP-15) PK-88 EPROM PLUS for older version of PK-87 :- 4.9152 MHz HC18/U parallel resonant crystal 220pF high stabilty capacitor NOTE: There are two versions of the PK-88 to date. In the context of EPROM upgrades they differ in the device used for U22 (in PK-88), the old version having a 74HCT4040 and the new a 74HCT4020. The 4020 allows a slower clock interrupt rate this being selectable by jumper 7, because of this there exist EPROMs for both rates. ICS say the faster rate is the standard rate, which means you do not need to change the device in the PK-87, U12. (The non-standard EPROM is issue 30-DEC-88 checksum $15 and needs the slower rate.) (The 4020 is a 14 stage counter as opposed to the 12 stage 4040 and can therefore divide the clock further but both are pin compatible in the pins that are used in the PK-87 and PK-88. If a change is made it will make no difference, except that if a slower rate is needed the 4020 will give the needed clock on pin 2. Once U 12 is relaced with a 74HCT4020, to get the slower clock rate cut the track going to pin 1 of U12, at the pin and put in a link from the track to pin 2 of the device.) Before starting it might be an idea to note the parameter settings so that any important ones can be re-entered at the end. Disconnect the cables and dismatle the TNC. Remove the link block from JP1 (beside lithium battery) and replace it on one pin only (disconnects battery from RAM). Remove the EPROM and put aside, it is needed once more for testing. Using a sharp knife cut the track on the underside going to pins 1 and 2 of U 8 (74LS139) and put in links on the underside between pin 1 of U 8 and adjacent ground track and between pin 2 of U 8 and the adjacent ground track. This alters the address decoding to the RAM in U 3 to A 15 only. Cut out out and desolder the pins of U 3 and U 4, the 8K RAMs. It is better to destroy the ICs than the printed circiut board !!!. Cut the thick track on the underside of the board going to pin 26 of U 3. Solder the 32K RAM in place of U 3 or solder in a good quality 28 pin IC socket (e.g. Turned pin). Link pin 26 of U 3 (RAM) to pin 26 of U 2 (EPROM socket) and link pin 1 of U 3 (RAM) to pin 27 of U 2 (EPROM socket). This adds the two extra address lines needed by the bigger RAM. Now insert the 32K RAM if a socket was used. Replace the PK-87 EPROM in its socket and check the board carefully for any shorts, bent pins or solder spldo link them up as below:- EXT MODEM 5 pin DIN 25 D connector 1 16 TX 4 o____ / _____ \ / / ___ ==\ O | | | / \\ || | | | | O= \======== | | \ \ +--------------- FIG 1 o 1 U 5 8530A On the underside of the board link the through hole on the track that has just be cut to pin 11 of U 20, see Fig 2. ____________ Bottom side of board _________ \ at top end of U 5 (8530A) \ o Connect -> =====\ o /= this hole ==O \==============/ to pin 11 ___________ of U 20 ______/ _________ \___ _______/ _______ \____ ________/ ___ \_____ FIG 2 _________/ o \ Pin 1 U 5, 8530A A small change on the PK-88 compared to the PK-87 is that pin 1 of U14 (7910) is taken to Vcc, this is done by linking pin 1 and pin 2 of U14. If the PK-87 has a 4.9152 MHz crystal put in the new EPROM and replace the board in the cabinet. Apply power and the unit should enter the auto baud routine and the unit can be started as from cold. If all is satisfactory turn the link block on JP 1 so it links the pins, remove power and reassemble the cabinet. (If the clock runs very fast and the timings are odd you have the wrong! version of the EPROM where the clock interrupt rate needs halving. You can either get a different EPROM or put in a 74HCT4020 and do the modification as per the NOTE at begining. For older models of the PK-87 the clock speed has now to be upgraded. Remove C 5 (680pF) and discard the it, then desolder C 3 (330pF) and put it in the position marked C 5. Put the 220pF capacitor in the position marked C 3 and change the crystal to the 4.9152MHz crystal. On the top side of the board between U 5 and U 14 (8530A and 7910) a thin track passes under R 12, cut this track, see Fig 3. \/ Cut this track | O o| 4 Top side of board 28 |o : ____| | : / _o| 5 U 5 27 |o : / / | U14 (8530A) |_________:/ | o| 6 (7910) p 26 |o +-+ | | | ! ! | o| 7 25 |o ! ! \_| FIG 3 R 12 On the underside of the board link pin 24 of U14 (7910) to pin 9 of U12 (4040). This puts 4.9152 MHz divided by 2 to the modem chip so it remains at 2.4575 MHz while the rest runs at twice the speed. If you have not made the modifications needed on the old PK-87 to the audio output make then now. They are to turn C 24 round so the positive is to the RADIO connector and if a TL082C is used as the opamp, to put in series with the audio output from it to the RADIO connector, a 100 ohm resistor to stop spurious signals appearing on the microphone line. The PK-88 EPROM should now be inserted in the socket and the board should be checked for any defects such as shorts, solder splashes or bent pins. The board can now be connected up and tested. If all is alright it will enter the auto baud routine and can be started as from cold. If there are no problems turn the link block on JP 1 so it links the pins, remove power and reassemble the unit. If you have problems with resets due to spikes on the 12 volt line, such as when you turn on a radio on the same power supply, either put a high value resistor in series with D 1 or just cut a leg of D 1. You should now have a PK-88 in false colours. If you have problems with overheating or unreliable operation I suggest you replace the Z8400A with a 6 MHz CMOS Z80 processor as the clock is beyond the rated speed of the Z8400A, the same can be done for the 8530A. With a CMOS EPROM and both CMOS Z80 and CMOS SCC the current consumption can be reduced to below 250 milliamps.