The ad stated: Advanced version of the T/S1000. Will run all prerecorded tapes for Sinclair/Timex 1000-ZX81. I ordered Feb 22 sent a money order for $35.95 to American Design Components, 62 Joseph Street, Moonachie, N. J. 07074. And received the PC8300 on Mar 06. Today I sent in a money order for $46.95 for another PC8300 plus a 16K Rampak.
Perhaps I’d best start with the physical dimensions of the PC8300. The box and the computer both are missing any markings to identify either the computer or the manufacturer. There is molded into the plastic case made “in Hong Kong”. I suspect that it was to be sold and the seller would put on his trade mark and or model number. The computer case (cabinent) is dark ivory or beige and is made of plastic but it does not have any shielding whatsoever. The case dissembles by removing 3 screws and then prying the case apart. There are snap catches molded into the plastic that hold it together. When you lift the top and the keyboard you will find the cable (16 wire ribbon cable) that connects the computer and the keyboard and if you are carefull you can tilt the keyboard back and take out four screws to remove the computer board itself. The case is 11 5/8 inches long by 6 inches wide and 2 1/4 inches high.
The computer board is 10 1/2 inches long and 3 9/16 inches deep with a 7805 regulator heatsink (black) that sticks up 1 inch and is 3 7/8 inches long. The external bus connector is centered on the length of the computer board. The board has 4 spaces for sockets to be installed if you want to clean out the solder from the holes for 4 2114 RAMS. All of the chips except the RAM are mounted parallel to the length of the computer board. There was no attempt to crowd the circuitry to compact the board.
The keyboard has 42 keys including 2 SHIFT keys and a RESET and has a LED power on indicator. The keys have action similar to the T/S1500 but the keys are slightly larger. The RESET key is to the right of the 0 key and there is a shift key on either end of the bottom row with the SPACE key between the period key and the SHIFT key. You have to spell out almost all commands since there are only a few like SIN, LINE NO., and DELETE are given. The keyboard is mounted to the computer top cover with molded in snaplock fasteners so you can get the computer out for repair.
With the computer in working position all the ports are on the back side from left to right they are TV, JOYSTICK (9 pin socket) EXTERNAL BUS, MONITOR, MIC, EAR, and DC POWER. The DC Power plug is the kind that has a hole in the center and the power plug for T/S 2068 will fit A B S O L U T E L Y D O N O T T R Y I T! The reverse polarity will fry the 7805 regulator at the very least and damage other things too. More about that later. Like on the T/S1500 the closeness of the other ports will hinder the use of certain peripherals.
The computer has the following chips: Z80 CPU, c4005 (their version of a ULA), AMI 8444 AB ROM, TMM 2016 RAM, SN74LS05N, and of course the 7805 regulator. Only the 7805 and the 74LS05 are soldered in the others are all socketed. And while it isn’t a chip the board has a speaker mounted on the near right hand end.
The external bus is given in the manual and in English and all the bus call outs are the same as for the ZX81, T/S1000 which I checked against one of my books.
I would have liked to give you a detailed tour of the keyboard but I pulled a bonehead. The power pack that came with my compouter was to be used on 220 VAC so I was thinking and noticed that the power plug on my T/S2068 would fit. So I checked the polarity but I missread or crossed the VOM probes any way when I powered up nothing on the TV and I heard a faint buzzing and I turned off and shortly I smelled the scorched electronic parts. From that point on I have been slowly trying to get it up and running. The Z80 is ok it works on one of my T/S1000 and ditto for the RAM. I had no way for sure to check the ROM or the ULA so at that time I didn’t.
I got the computer and keyboard out of the case and got the regulator out, cut leads and got the holes cleared of solder and got another regulator soldered in place and I rigged up a transformer with two 110 VAC primary windings and wired them up serries adding and soldered that to the prongs of the 220 VAC power supply. I fired up the computer board with the chips out of their sockets and no smoke and LED lit up. Fine so I unplugged and plugged in the chips and with the computer board and keyboard loose on a wood surface I fired up again. Still no TV action but a transistor on the computer board cracked open and smoked. Now I need to find a MH9013 transistor or its equivalent. Either the reversed polarity caused the transistor to fail and to go when I powered up or else the the circuity on the bottom of the keyboard touched something on the computer board and shorted out.
Now I am trying to find a replacement transistor and what I may have to do is to remove as carefully as I can the other MH9013 transistor and use a transistor checker to find out what it is NPN or PNP and maybe the gain and whatever else I need to know to find a replacement. A friend has told me that a 2N2222 or its compliment will very likely work. But before I try to remove the transistor I will see if it can be checked in circuit.
The PC8300 looks like an attempt to duplicate the T/S1000 with a similar but different enough to avoid lawsuits. The more I looked at the computer board the more I thought that the board was enough like the T/S1000 for the ROM and the ULA chips to work. I tried that and I may have blew the chips but I feel the pinouts are very likesly the same. So I have ordered another PC8300 but I will be very carefull next time.
I had received a letter from a T/S friend the day after I received my computer and he stated that he had ordered one. And when I blew mine I called him up to warn him but he already had his up and running. He had ordered his with the 16K rampak and it all worked. The rampak looks like the Timex 1016 except it is white. His computer came with a 110 VAC power supply.
He tried to load in some programs and he found that all basic programs loaded all right but machine code puts the computer in a cycle printing out the last few lines of the program clearing the screen and repeating. and RESET would not stop or clear the program out of the computer, he had to pull the plug to get control again.
Part II next issue.