Correction of +2 hardware errors

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  • edited May 2014
    Renegade wrote: »

    BTW, what type of speaker are you using?

    A 32 Ohm one from an old headset
    'Interface 1bis' for the Sinclair ZX Spectrum
  • edited November 2014
    velesoft wrote: »
    Next bugs are in firmware of HAL10H8( or PAL10H8 ). This is port decoder and memory controller.


    - data of paging port 7FFD are rewrited also if CPU read of port 7FFD (write floating bus data)

    I remember this one when I was a kid , on some games pressing the bottom row of keys would cause games to crash/reset. Nice to know I was not crazy
  • Sorry for replying to an ancient thread, but I figured this would be fitting here -

    How the heck have these machines ever worked? Why didn't people just bring them home, try to use them, and return them to the shop as broken? I understand fixing things that have rotten in the past 30 years, or have become incompatible with modern hardware (like displays), but... reversed transistors and stuff?
    http://iki.fi/sol | http://iki.fi/sol/speccy/ | https://github.com/jarikomppa/speccy
    http://goo.gl/q2j0NZ - make ZX Spectrum choose your own adventure games, no programming needed (release 3)
  • I took my +3 with it's faulty sound and exchanged it about 3 times, each time waiting for different batches, in the end I just gave up because they were all like that. But I still kept it.

    Now we have the internet, so if there was a design or manufacturing flaw, you'd know you weren't alone.
  • RobeeeJay wrote: »
    I took my +3 with it's faulty sound and exchanged it about 3 times, each time waiting for different batches, in the end I just gave up because they were all like that. But I still kept it.

    Now we have the internet, so if there was a design or manufacturing flaw, you'd know you weren't alone.

    The ones I've seen on sale, as well as the one I bought, are clearly used ones, not bought and shelved.. so they must have worked *somehow*. Maybe the RF stuff worked on old TVs easier? Or maybe the a screen plugged to the RGB connector didn't care that the sync signal was broken..? I just can't figure out how they might have worked =)
    http://iki.fi/sol | http://iki.fi/sol/speccy/ | https://github.com/jarikomppa/speccy
    http://goo.gl/q2j0NZ - make ZX Spectrum choose your own adventure games, no programming needed (release 3)
  • I think the modulator RF output is still 'fine' in those machines, which will have been 99% of the use cases.
  • edited March 2016
    kenwonders wrote: »
    I think the modulator RF output is still 'fine' in those machines, which will have been 99% of the use cases.
    Exactly :D
    Back then, Speccy and other similar home computers (C64 etc) were mostly used with small screen TVs. Most of these only had UHF arial inputs. As the RF/UHF output worked on all the machines, the user would have been none the wiser.

    Mark
    Post edited by 1024MAK on
  • Sol_HSA wrote: »
    RobeeeJay wrote: »
    I took my +3 with it's faulty sound and exchanged it about 3 times, each time waiting for different batches, in the end I just gave up because they were all like that. But I still kept it.

    Now we have the internet, so if there was a design or manufacturing flaw, you'd know you weren't alone.

    The ones I've seen on sale, as well as the one I bought, are clearly used ones, not bought and shelved.. so they must have worked *somehow*. Maybe the RF stuff worked on old TVs easier? Or maybe the a screen plugged to the RGB connector didn't care that the sync signal was broken..? I just can't figure out how they might have worked =)

    The +3 sound fault was very well known. I remember letters to the technical help section of Crash asking about the sound quality on the +3 to which the expert replied that all +3's have rubbish sound quality.

    There was even a feature in a later crash issue that showed lots of european videogames (power and magic, senda salvaje...) that basically said at one point - we think this game probably has brilliant music... but the sound quality on our Crash +3 is so bad we can't really tell!
  • 1024MAK wrote: »
    Remove C31 (applies audio sub-carrier to TEA2000 input) and instead connect this signal via a new capacitor between IC11, pin 4 and the emitter of TR1. This means that audio is still available from the RF TV connection, but the signal is not pointlessly present on the composite video output. Monitor should now produce a good colour picture from the composite signal.

    Change R38 to 5.6k. This increases the level of the AY generated audio so that it is now only slightly quieter than the ULA/cassette generated sounds.

    Please, does anyone have clear photographs at various angles of the above modifications showing how it should be done? I've watched the video but the end result picture at 28.08 is unclear as to where the solder points are next to the TEA2000 chip. Yes, I am a complete beginner at this and clear photos really will help not only myself but everyone who wants to get these fixes done.
  • On my +2 Grey issue 3 Z70500 - 8639 date.
    Going by the circuit diagrams, the R38 is for the RF sound output only with an 18k resistor (Brown, grey, orange, gold) as per Amstrad.
    I swapped it for a 10k resistor (brown, black, orange, gold) as it was the only spare that I could find at the time and it was nice and loud, almost matching the beeper volume.
    Today I've got hold of a 5.6k resistor (green, blue, orange, gold) thanks to a fresh arrival of an unwanted video recorder and removed the 10k resistor from the +2 and popped in the 5.6k. However, the sound is quieter than the 10k resistor, swapped them over to retest and yes, the 10k resistor is louder than the 5.6k via the RF output.
    I swapped them over again to listen and back again - I'm keeping the 10k inside the +2, the 5.6k is now in the bits box.
    I'm no expert on this - my electronics technical knowledge is zero - maybe 0.5 on a good clear day (I can wire a plug create a battery lightbulb circuit with a couple of bits of wire, unsolder bits and swap them around with the aid of good photos) reading that the 18k resistor gives a volume setting, 5.6k should be louder (less resistance - how I understand it) and the 10k should give something between them, but on my +2 the 10k is louder.
    I know that I shouldn't be using the RF due to crap picture output, but the sound output is a whole lot better than the socket.
  • MatGubbins wrote: »
    Today I've got hold of a 5.6k resistor (green, blue, orange, gold)
    Except that that colour code is for a 56k resistor!
    Mark
  • Ah, that must be why it's quieter and I got the calculations wrong. I've now found this site to play with

    http://www.digikey.co.uk/en/resources/conversion-calculators/conversion-calculator-resistor-color-code-4-band

    and yes, it is a 56k. Will have to wait for the next victim video recorder to shuffle along.
    See, I know bugger all about electricals... best that I stick to play-doh and blutack :-)
    Well, great laugh and goes towards experience... ta!

  • Another dead video player appeared yesterday and had a 5.6k (green blue red gold) resistor (along with a good handful of other values, a nice composit socket and some copper wire to unwind), unsoldered, the +2 taken apart, then the 10k resistor I inserted a few days ago (was originally an 18k brown grey red gold) removed from R38 and 5.6k inserted.
    Teseted with
    10 PLAY "c","e","g": BEEP 1,0 : GO TO 10
    
    and both are now at the same level for the RF / TV output. Yup very nice indeed.

    Fixing the AY on composite via the sound jack on the back on the +2 has been fun too!
    I have not yet managed to get the magical 330k, 3.3k and 39k resistors yet though.
    I have removed the 10k (brown black orange gold) resistor from R37 and inserted a 2.2k (red red red gold) resistor - this has boosted the AY output to a nice volume
    and then removed the 10k (brown black orange gold) resistor from R45 and inserted a 18k (brown grey red gold) resistor - this has reduced the beeper output to nearly match the AY output
    The result is clearer and with a great composit picture - there is a slight hum, from the tape deck I assume, but does not really notice.
    (the 18k resistor was now spare from R38 as above and the 2.2k resistor was from the video recorder)
    Just need to find/buy the correct capacitors and inductor to make the TEA2000 filter to complete the composit mod.

    Yeah, I know the image using the RGB SCART is better but my Matsui LCD screen doesn't like the SCART input - it works on other LCD screens though.

    Great fun!
  • 1024MAK wrote: »
    schombi wrote: »
    One thing is still not clear to me - maybe I just missed that bit of information. Do all +2 (grey) suffer from these problems and should be fixed or is there a difference between greys made in Taiwan and made in UK?
    Not sure about all problems, but the transistors being fitted incorrectly may only affect some greys made in Taiwan - see http://www.worldofspectrum.org/forums/showthread.php?t=44025

    Mark

    My +2 with Issue 1 board has all three transistors - TR4, TR5 and TR7 - fitted the correct way. :)
  • velesoft wrote: »
    Next bugs are in firmware of HAL10H8( or PAL10H8 ). This is port decoder and memory controller.

    List of bugs:
    - absent input signal RFSH from CPU for eliminate ula effect known as "screen raining / snow effect"
    - data of paging port 7FFD are rewrited also if CPU read of port 7FFD (write floating bus data)
    - access to I/O ports slow-down CPU (ula slow-down cpu with same way as memory access)

    Is possible replace this chip with new PAL10H8 or GAL16V8 with fixed firmware, but we need also connect RFSH from CPU Z80 to pin 11 of this chip. Eliminate raining effect is good feature, disable reading from port 7FFD is also good, but make fast I/O ports cause small incompatibility with original timing in some ZX demos...

    Here is my version of fixed chip with original I/O space contention:
    http://velesoft.speccy.cz/zx/umbrella/umbrella.htm


    Just how critical is the correction of this bug?
    Will some games not work or have issues? In that case which ones?

  • 1024MAK wrote: »
    Sound noise

    Thanks to Ingo for this bit.

    The noise is caused by the tape amplifier. It is permanently supplied connected to the ULA pin. Try not to change this supplying by connecting it behind the motor switch. The amplifier needs a big electrolytic capacitor to get a smooth power line. Switching this big capacitor to the 5V line would cause a drop in this line and so a computer crash.

    There is a simple way to remove the noise. Insert a (small REED-) relay that is connected with its coil parallel to the motor. Cut the white line of the cable between tape drive and computer and insert here the relays switch. This way the output of the amplifier is connected only if it is needed.

    Maybe there is special noise cause by a oscillating output stage of the tapes amplifier. If this is the case insert an additional resistor of 100 ohm in series to the white line as well as a capacitor of 100pF from this line to ground. In two cases I had to do this. An additional effect is then that the drive works more reliable.

    Greets Ingo.

    I'm thinking of doing this modification. Could anyone recommend which type of relay to buy?
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