Which ports are which on this Soviet ZX Spectrum clone?

Question

Today I got my (first) Soviet ZX Spectrum clone. The person who sold it to me had inherited it and had no idea how it worked.

It seems to be a home-made clone, rather than a factory-built one. See picture in case I'm wrong about this:

I have looked at the most similar ones I could find online, but the ports seem to be in an unpredictable order on different clones. I show them upside down here to match the subsequent picture from the inside of the machine. I take it the port with the (in fact upside down) T is the electricity adapter socket, but would value confirmation of this before I fry the computer by plugging the electricity adapter (which I have) into the wrong place.

Here is a picture of the ports as they are connected to the motherboard. As in the previous picture, the reset button is on the far right.

And here are the ports up close from the inside. Again, I'm guessing the two thicker wires connected to the port next to the reset button confirm that it is the electricity adapter.

So my question is - can anyone with more knowledge of Spectrum (clone) architecture and/or electronics confirm that the port next to the reset button is the electricity adapter, and divine what the other ones are? For practical purposes, the monitor / TV out and EAR would be the most useful ones, though I take it these Soviet clones often had things like joystick ports, and I got a five-pin joystick together with this purchase.

I should say that all the cables I have are five pin (DIN?), and though the middle port is seven pin, I've already experienced successfully using a five pin cable with a seven pin port (on my Elekronika BK-0010-01).

Answer 1

No need for any special Spectrum knowledge. It's about power, and there is no rectifying, no appropriate sized capacitor and voltage control elements on this board, so it most definitely does not take AC but rather some well regulated DC input. I'd assume 5V. So operating it at some arbitrary AC and higher voltage my fry it right away.

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Usually the start would be some laboratory PS (always a good investment if you plan to play with old stuff. And don't buy cheap here). But in times of need some USB charger might as well work for 5V (*1). Clip the connector, detect the orientation.

In either case, look at the board if there are markings for ground or +5V. If lost, take a look at the chips. For example all RAMs typically have their ground on pin 16 - the top rightmost pin (mark on top). See where these traces are going and connect to the power lines, and you've got ground. Now you already can't damage polarity. Next is finding the +5V (*1).

Since all is wired with single white wires (*2) and connected to various parts of the board, it's your turn to follow all of them, as the pictures don't really reveal a lot. Adding some highres from direct above and below the board might allow others to help.

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SU computers often had external PS to reduce potential dangers within the device. In fact, school installations more often than not had central 5V or 12V routed to each desk, so the pupils only had contact to low voltage.

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What you got there is a LENINGRAD-1 board produced by Tachion (тахион) in Leningrad - today's St.Petersburg. The board was designed by Sergeij Zonow around 1988, who then founded Tachion to mass produce it and sell it to companies building their own versions of the Spectrum or hobbyists fitting them in home made cases. The resulting machines had many names and designs. Like Delta-N, Rita or Jaguna and endless variations of ZX/Specy/Spectrum in English, Russian or mixtures thereof and many regional names like Dubna, Leningrad, Ural, Krasnojarsk, Moskow, and so on.

The Spectrum was in Russia like the VC20 or C64 over here ... in fact even more so, as it was, until the late 90s the eastern European machine. The scene was exploding from like 1988 to the mid 1990. There were literally hundreds of meetings each month. And the Leningrad board was at the core of this movement. It also was that movement that inspired the Selenograd chip works to create a ULA equivalent to allow further integration. Selenograd was also the place doing the Z80 clones for the SU using East German technology.

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*1 - Not sure, but I think I remember the Spectrum also needed +12V. The connector seams to have 3 pins, but looking at the picture I can only see two wires. Also from other details I'd say this board seams to be designed for a single voltage.

*2 - Reminds me of the floppy drive for the Estonian Juku 5101 computer. A simple enclosure for two 5¼ inch drives, but instead of flat ribbon, the connectors were wired individually all white wires. A hell of a work for a mass-produced machine, and even more so to debug.

Answer 2

Looking at the linked schematic and the photo of the internals, I'd say the ports are the following (listed from the reset switch over)

1. Reset
2. Power
3. Composite video (or possibly monochrome luma only)
4. Joystick
5. Tape
6. RGB video

The port with the two thicker wires is almost certainly the power, as you identified, backed up by the "upside-down T" symbol on the back of the case indicating the ground pin. You'd have to show the underside of the board to be sure though.

Both the composite port and RGB port connect to the same area of the board (which is near to the RAM; chips with green capacitors on top) and you can see "R", "G", and "B" silk-screened on the board there. The RGB port has six wires (R, G, B, Sync, ground, and shield), and the composite port has three (video, ground, shield).

The tape port and joystick go to the same part of the board as the wires from the keyboard, indicating all the I/O is over in that area. The tape port would be three wires (in, out, ground), and the joystick port with 6 wires (4 directions, button, +5 volts).

Answer 3

Only you can decide which port is which as you are the only one with access to your HW. I would use multi-meter and or short circuit tester:

1. Power supply

   I see no stabilisator nor DC/DC nor AC/DC converters so the power supply is external. Here is first Z80 pinout image I found in Google you can check against any Z80 datasheet.

   

   It is look from top side of the chip (just like when you look at the real Z80 on your board). Notice the up marker (the engraved half circle or rectangle or sometimes just dot on top middle) so yo now how your chip is oriented. Now just trace where:

   pin11 +5V
   pin29 GND
   

   are connected to your ports. be careful and check both directions of current that means if you find that some pin of your port is connected to GND for example make sure the conection is there if you swap cables +/- if the conection gets lost you got some diode in the path and you are not in direct connection. Also capacitors tent to false positively show you connection which is not there but that last usually only few seconds. Test only with small DC voltage multimeters use low current and small voltage for this so you should be fine.

   This should have you located the power supply port easily. The cables to it should be the thickest (but that is not rule for home made stuff) My bet it is the right most connector with 2 cables only (on the image below).

   So you need +5V 1A DC (direct current) power supply you can salvage any USB charger (they are usually 0.8 - 1 A) but using a lab power supply with current limiter is better idea at least until you bring the computer from the dead as you can set low current limit and check if there is no problems without actually burning the chips ...

2. ULA

   You should locate ULA chip(s). I can not recognize it on your image as I am used to DIL40 version. There are however versions of ULA distributed to more smaller chips 4 I think.

   As you already have keyboard try to trace to which IC(s) it is connected that should be the ULA.

   Another way is to identify all the IC parts on your board. There should be memories 6116 or 4116 or something like that (beware Russian chips use very different numbers) there should be some TTL multiplexors and may be also some TTL gates like AND/OR/XOR/NOT The TTL chips start usually with 74 I see quite a few of them on the image but there are a lot of the russian chips and I do not recognize those at all as I did not use them so much (just few times when there was no other choice). What ever will be left is most likely the ULA. Here is my wild guess (the big chip DIL40 is the Z80 CPU)

   

   Now try to find out yours ULA pinout and trace the pins of interest. That will let you find keyboard, sound out , tape in and video out.

3. Video

   I would start with video as without it is hard to diagnose/use your ZX. The video output usually uses TV modulator circuit which is usually a small circuit enclosed in Faraday's cage casing (small metalic box) with TV antenna connector going directly out of it. I see no such stuff on your board. So either it uses different type of video signal or the small metalic part I marked is the modulator. Anyway the modulator chip usually uses some TDAxxx chip so if you see that you have it (again Russian counterparts can have different designation).

   So locate the video modulator chip and look for its pinout. There you should see if it needs additional voltages like -12V. If it does trace where it is connected to. Either it will lead directly to some port or to some circuitry that will create the voltage from +5V in which case you do not need additional voltage for power supply.

   Beware in case of more than one voltage power supply all the voltages should have specific order of turning on and off. If not provided you can seriously damage the chips using them (IIRC that was the self destruct reason of original ZX spectrum due to dried out capacitor in DC/DC converter circuit). But if chips use only single voltage you should be fine (as the newer clones does).

Anyway all the ports pinouts you need trace to the IC chips they are interconnected with/to.

The electrolytic capacitor I marked with red is most likely the power supply filtration (most likely connected to +5V and GND) for the whole computer and the design looks pretty old RVHP style so it is most likely dried out already and should be changed (otherwise you risk random reset or crashes of your computer). I see only one other electrolyte (on the opposite side of CPU) small black cylinder that might need to change too but it looks much newer and also it most likely is not that important (my guess it is just CPU power up reset circuit reseting the CPU when you plug in/turn on the power supply) but that is just my guess.

[Edit1]

Well as mnem and jules pointed out there might not be an ULA present there is another way to identify the video. Simply plug in the power and hook up an oscilloscope to the port. Look for video signal there. To make this easier try to blindly program Border color different than white in BASIC. Now you are looking for signals with specific frequencies and shape. See PAL video timing specification. So measure each pin of the undetermined ports and deduce from shape, voltage levels and frequency what the pin is. Flat lines are usually just shield or GND or inputs.

Sound output can be deduced similarly ... just try looping some BEEP in basic and look for sound square wave output with hear-able frequency.

I know coding in Basic blindly is not easy but it is doable I did it before with my ZX clone :) ... You can train on different machine or in emulator ...

Answer 4

Computer "Composit" (Leningrad+). http://sblive.narod.ru/ZX-Spectrum/Composite/Composite.htm

http://sblive.narod.ru/ZX-Spectrum/Composite/CompositeSCH-MONT.gif

Left to right:

KEMPSTON

1. Right
2. Left
3. Down
4. Up
5. Attack/Fire
6. Common

TAPE

1. Input
2. Ground
3. Out

TV

1. Red
2. Green
3. Audio Out
4. Blue
5. Video Out
6. Ground

+5V 0.6 Ampers

1. +5 Volts, 1 Amper

2. Ground

3. Ground
4. Ground
5. Ground

The circuit board is similar to Leningrad-1. http://sblive.narod.ru/ZX-Spectrum/Leningrad48k/Leningrad48k.htm

Answer 5

Use the schematics http://speccy.info/%D0%9B%D0%B5%D0%BD%D0%B8%D0%BD%D0%B3%D1%80%D0%B0%D0%B4_(%D0%BA%D0%BE%D0%BC%D0%BF%D1%8C%D1%8E%D1%82%D0%B5%D1%80) to trace everything up to the connectors. Any other way would be just guessing.

You can power the board from any widespread USB charger, 2A would be enough. Trace common power pins (ground: pin 7 at any DIP14 IC or pin 8 at any DIP16 IC, 5v: pin 14 or pin 16) to the one of the connectors (SUPPOSEDLY that is DIN-3 one) and then build the cable from any USB cable, using DIN-5 or DIN-3 male plug.