Troubleshooting Robik, russian clone

bola_dor
Posts: 398
Joined: Wed Oct 02, 2019 5:32 am

Troubleshooting Robik, russian clone

Post by bola_dor »

Hi, I have little experience with ZX Spectrum and Argentinian clones that are 99% as the original ZX but none with this russian (I think it's Ukrainian from the early 90's).
Its video output is RGB it doesn't have a video encoding circuit. As I don't have any 15khz RGB monitor or SCART TV Ive made a simple circuit to have a composite B/W sugnal (I copied it from the CPC 464 schematics that doesn't have a Video encoding IC either) my TV interprets something as color anyway..
Clearly something is not going well.
The ROM is somewhat different, it supports Cirilic characters and the boot screen it's supposed to be blue?.. sometimes it showed the start message shortly but I couldn't get it in video.
Keystrokes are still beeping when you press them. So I tink it may be not completely dead unless it has some dumb beep circuit..
IC names are completely different.
20220708_035740_0.04.166.jpg
20220708_035740_0.08.699.jpg
I've checked the ram.. are 8 ICs at 5v and I found they are pin compatible with 4164. All data, cas, in, out lines are pulsing. I can't figure out how are they multiplexed or addressed..
At Z80 CLK is OK, /RFSH is pulsing. All data and address lines are pulsing, then M1, WAIT, BUSRQ, WR, INT , NHI IORQ are fixed High,
HALT is down.
The others are pulsing...
I refuse to think the ROM is dead as some times it shows up briefly but probably is not being read.
I think the machine doesn't have an ULA but logig ICs..
Sadly rusian designation is different and difficult, for me at least.
I don't know exactly what the Z80 control lines should look like, I've only learned that/RFSH pulsing means is alive but the /HALT being down keeps it doin nothing, (or I may be wrong )
20220710_011756.jpg
I am on the process of trading this machine. IF I can't make it work easily I am afraid I will give it back... it's otherwise in great condition..
Ernesto
ZX80 USA, ZX81UK, ZX Spectrum, ZX Spectrum+, ZX Spectrum 128+ UK, ZX Spectrum +2/A, Sinclair QL, CZ1000, CZ1500, CZ2000, CZ1000Plus, CZ1500Plus, CZ Spectrum, CZ Spectrum Plus, TK83, TK85, TK90X, TK95. TS2068. And more to come :D
bola_dor
Posts: 398
Joined: Wed Oct 02, 2019 5:32 am

Re: Troubleshooting Robik, russian clone

Post by bola_dor »

OK,
Some more done,
I realized that HALT line goes to nowhere but the border connector.. so this is not the problem.
I found another RAM bank of 8 IC
20220710_202419.jpg
(I think these are 16x1bit)
Pin 2 seems to be not connected
And Pin 14 shows a bad behavior
The first of then pulses like this
20220710_204948.jpg
The others changes periodically from that to this:
20220710_205142.jpg
(Always at Pin 14 DO, Data OUT?)
Screenshot_20220710-014817_Adobe Acrobat.jpg
EDIT:
pin 2 are linked to one KP1533MP23 IC and pin14 to another (forth from the top at the right on the last picture) I guess those are multiplexer ICs but I couldn't find anything about them in the net. The one linked to memory's Pin 2 is pulsing only at Pin 4 and pin 14 the rest are either high or low. I see that thus can be a fault at this IC or it is responding to another fault.. neither of them is hot...
Ernesto
ZX80 USA, ZX81UK, ZX Spectrum, ZX Spectrum+, ZX Spectrum 128+ UK, ZX Spectrum +2/A, Sinclair QL, CZ1000, CZ1500, CZ2000, CZ1000Plus, CZ1500Plus, CZ Spectrum, CZ Spectrum Plus, TK83, TK85, TK90X, TK95. TS2068. And more to come :D
alecu
Posts: 3
Joined: Tue Jul 12, 2022 9:49 pm

Re: Troubleshooting Robik, russian clone

Post by alecu »

Hola Ernesto, last week I got a Robik too! Seems there are at least two now in Argentina :lol: :lol: :lol:

When turning it on, it never went past the initial welcome screen, and it started making a continuous series of beeps and flashing one specific char.
I opened it, and realize it was time for me to start learning about soviet IC nomenclature.

First I tried checking the electrolytic cap next to the CPU, so I unsoldered a leg to test it. The first problem showed up there, when a circuit trace got unstuck from the motherboard... ouch. It was well within range, so that was not the problem, and I decided not to check the other two caps, since they were not close to where I suspected the problem to be.

As you mention there are two banks of 8 chips of RAM: КР565РУ5 (KR565RU5) which is the upper 32kb of RAM and КР565РУ6 (KR565RU6) which is the lower 16kb of RAM. Since when booting I clearly saw the familiar initial Spectrum ram checking pattern of: first black screen with red traces and then the screen cleared up and the welcome message (but white on green!), I started suspecting that it might be a ROM or RAM failure.

And if it was RAM, I suspected the upper bank, since it failed after initing. So before desoldering anything I tried "piggybacking" a working ram chip in turns on one of each upper RAM. I read somewhere that this method sometimes helps... (was it Noel's retro lab? perhaps). But I tried on all chips, and got nothing useful.

So I found a ROM copy online, and was going to desolder both ROMs and try to compare them. But I didn't have spare sockets for the ROMs, and did have some for the RAM, so I took on the arduous task of desoldering all upper RAM!
IMG_20220711_000238.jpeg
I'm not the best at this, so even using a desoldering gun I ended up unsticking five PCB traces, that I then had to repair with small pieces of cable underneath after soldering the sockets. I suggest a lot of care with this, these PCBs are super crappy.

But luckily after replacing all upper RAM, it started working ok!
In the end I found that only one chip was faulty, but now it will be much easier to fix if any of the upper RAM goes bad again.
Playing a bit with BORDER, I noticed that the info I found for building the RGB cable was backwards, and that the boot screen ought to be white on blue! I fixed the cable and now it was working properly!
IMG_20220711_032714.jpeg
As you probably guessed from the basic listing above the "zero" key is not working ok. The keyboard cables are crappy, I had to resolder a few after the fixes. But that key is not working at all, I'll probably switch it with the "comma" or some other.

Mine came with the manual and schematics, but in case you need them I found them here when searching for the ROM. If you need to I can scan them if the versions there are too blurry, but mine are a bit blurry too.

Un abrazo che, y suerte con eso!
alecu
Posts: 3
Joined: Tue Jul 12, 2022 9:49 pm

Re: Troubleshooting Robik, russian clone

Post by alecu »

Regarding the soviet chips, I found these links handy to help me understand my way around:
https://ganswijk.home.xs4all.nl/chipdir ... /chips.htm
https://elcomps.com/en/a76
bola_dor
Posts: 398
Joined: Wed Oct 02, 2019 5:32 am

Re: Troubleshooting Robik, russian clone

Post by bola_dor »

alecu wrote: Thu Jul 14, 2022 4:18 am Regarding the soviet chips, I found these links handy to help me understand my way around:
https://ganswijk.home.xs4all.nl/chipdir ... /chips.htm
https://elcomps.com/en/a76
Nice!!!
It's always a joy when the machine finally starts up!!!!
Well I guess we can officially start the Argentinian Robik and Soviet clones Club then.
I have manualsnand the schematics too although I find it a bit useless.. is a bit better readablenthan the on line copy but it s not clear at all for me. Lines end on references I couldn't find anywhere.
Now I am reverse engineering from the lower bank where I found bad wr/rd signals..
The capacitor you mentioned is the reset one. If the machine starts booting up it shouldn't be the problem.
What I notice is a lot of base noise all over the board so I guess enhancing the the coupling is not a bad idea..
Ernesto
ZX80 USA, ZX81UK, ZX Spectrum, ZX Spectrum+, ZX Spectrum 128+ UK, ZX Spectrum +2/A, Sinclair QL, CZ1000, CZ1500, CZ2000, CZ1000Plus, CZ1500Plus, CZ Spectrum, CZ Spectrum Plus, TK83, TK85, TK90X, TK95. TS2068. And more to come :D
User avatar
1024MAK
Posts: 5103
Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: Troubleshooting Robik, russian clone

Post by 1024MAK »

The HALT pin on a Z80 is an output to indicate that it has executed a HALT operation code. The Z80 will now wait and do nothing more until it either receives an interrupt (either INT or NMI), or is RESET.

The ZX Spectrum ROM code does contain a number of HALT instructions. But as maskable interrupts are normally enabled, and the video system (ULA in a Sinclair model) always pulses the Z80 INT line at about 50Hz, the execution of the program should normally continue after waiting for the interrupt.

Of course, if the ROM is faulty, or there is a DRAM fault, or anything else that can cause the Z80 to read and execute garbage, anything can happen, including the maskable interrupts never getting enabled, or becoming disabled.

On the type of 1 bit wide DRAM used, normally pin 2 and pin 14 are connected together (most designs where a Z80 is used including the Sinclair ZX Spectrum), but not in all designs.

In my experience, DRAM chip failure is the most common across the ‘home’ computer models of the early to mid 1980s.

Good luck ;)

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
bola_dor
Posts: 398
Joined: Wed Oct 02, 2019 5:32 am

Re: Troubleshooting Robik, russian clone

Post by bola_dor »

Some progress (?)
I did some reverse ingeniering..
In this case 16kbit ram that uses 5v+ only had pin 2 and pin 14 in different buses.
Both are connected to separated IC equivalent to 74LS374. I had to study.
Captura de pantalla 2022-07-24 21.39.01.png
Those are 8bit latches that output the same bit on tue imput when a clock signal is its rise up edge and if the /enable output pin is down. There are several of this ICs in the board..
Thing is I don't have a good signal on any pin 2 (Data Write) coming from this IC but it's inputs pulses OK... the I thought that there was the problem and exchanged it with its occidental equivalent.. nothing changed. Then I reviewed it's /OE and CLK lines.. OE is connected to GND.. without even a resistor. That just keeps the output open so I didn't care much.
But CLK has a pull up. ( its a 390ohm resistor and a small ceramic like a RC filter).. then I thought that the rising edge wouldn't be present.. BUT there are two other 734 equivalent ICs linked to the same CLK line and their outputs pulses well... so I don't know how that works but thought the broblem may be the ram itself so. I preceeded to desolder all the lower RAM bank, test the ICs
20220801_001848.jpg
20220727_001624.jpg
( found two/ eight were dead). Cleaned the board, checked severla times for shorts ot cutted tracks, fixed some solder splashes. And fitted two 4164 RAMs in place along with the other soviets ones. All tested several times as being good. The extra Addres pin 9 in 4164 is linked to pin 10 in the board so it didn't need any modification...
It didn't work.

Screen pattern changed perhaps. Note how it responds to a key that was kept pressed...
Ernesto
ZX80 USA, ZX81UK, ZX Spectrum, ZX Spectrum+, ZX Spectrum 128+ UK, ZX Spectrum +2/A, Sinclair QL, CZ1000, CZ1500, CZ2000, CZ1000Plus, CZ1500Plus, CZ Spectrum, CZ Spectrum Plus, TK83, TK85, TK90X, TK95. TS2068. And more to come :D
User avatar
1024MAK
Posts: 5103
Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: Troubleshooting Robik, russian clone

Post by 1024MAK »

For schematic diagrams and similar, because the forum software uses lossy compression on pictures, can you please put these in a zip file, then attach the zip file.

If the computer is responding to keyboard input, then BASIC is clearly running. That means that the fault on the board is restricted to the digital video circuitry. As the processor, ROM, “lower” RAM, control circuitry, address, control and data busses must all be working for BASIC to run.

Either the digital video circuitry is reading a mixture of garbage and some correct data when trying to generate the video display (data line fault) or some of the video address lines are not working correctly. Or it’s a fault within the digital video circuitry itself.

For people wondering about this clone, the Wikipedia article gives a bit more general detail. Search also for “ Робик компьютер ”. And more information here https://speccy.info/Робик.

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
bola_dor
Posts: 398
Joined: Wed Oct 02, 2019 5:32 am

Re: Troubleshooting Robik, russian clone

Post by bola_dor »

My partial schematic here: https://www.dropbox.com/s/pp72uif115i9u ... 1.png?dl=0

It's a screen capture.. I'm not an expert with this CAD, or any one...

This computer has no ULA so the video circuitry is exposed there. It came with the schematics, It's the same I found online. Barely legible and I couldn't understand it. May be because of mi not knowing how to read it. Its full of references that I don't know how to follow.
I converted it to pdf here https://www.dropbox.com/s/3ysewffh5s9z3 ... 1.pdf?dl=0

Thanks a lot!
Ernesto
ZX80 USA, ZX81UK, ZX Spectrum, ZX Spectrum+, ZX Spectrum 128+ UK, ZX Spectrum +2/A, Sinclair QL, CZ1000, CZ1500, CZ2000, CZ1000Plus, CZ1500Plus, CZ Spectrum, CZ Spectrum Plus, TK83, TK85, TK90X, TK95. TS2068. And more to come :D
User avatar
1024MAK
Posts: 5103
Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: Troubleshooting Robik, russian clone

Post by 1024MAK »

With the original schematic, I think you will find each IC (chip) has a grid reference as an identification rather than a normal number.

So instead of say IC3 or U3, you may get E5, based on an appropriate grid on the circuit board.

A lot of Soviet era chips are based on western parts, so glue logic is often based on 74 series logic. However the part numbers are written in the Cyrillic alphabet. I must admit, I find this tricky to understand, especially when handwritten.

There are actually various different logic diagram symbols used around the world. This page shows some.

The USSR integrated circuit designations are listed here. This web page has a similar list.

Western equivalents (but check the pin-outs) to USSR chips are listed here.

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
Post Reply