Correction of +2 hardware errors

edited November 2014 in Hardware
This is a collection of various pieces of information picked up from various places, including a lot from this forum. I have edited it and reworded it.

As it was originally intended only for my own use, I did not add most credits. But a bit thank you to all the people who posted on this forum with helpful hints and tips, you know who you are ;).

Correction of +2 hardware errors:-

TR4, TR5 and TR7 (all type 2N3904) are fitted the wrong way round. Desolder them, check their gain, if low renew else refit them the opposite way round to the marking on the PCB so that they work correctly.

TR4 provides the composite video output on pin 1 of the RGB socket (from pin 6 of the TEA2000).
TR5 provides the vertical Sync. (V.Sync.) output on pin 5 of the RGB socket (from pin 23 of the "ULA").
TR7 is the transistor that pulls the ULA's /IOREQ line high when A0 is active.

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.

The circuit diagram shows video output options called Standard and Peritel. The links in most +2 machines in the UK are connected as shown for Standard, but resistors R12-R13 and their associated diodes are also installed. This creates a tri-level RGB output (The brightness mixed with the RGB).


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.
__________


Mark

PS Does anyone know why TR7 being fitted incorrectly appears to have no known affect?
Post edited by 1024MAK on
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Comments

  • edited January 2013
  • edited January 2013
    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
  • edited January 2013
    If all three TR4, TR5 and TR7 transistors were wrongly installed in reverse by amstrad (except just tr4), why didn't anyone else mention it?
    Even at Velesoft's web page, there's only info about fixing the tr4....
  • edited January 2013
    gtsamour wrote: »
    If all three TR4, TR5 and TR7 transistors were wrongly installed in reverse by amstrad (except just tr4), why didn't anyone else mention it?
    Even at Velesoft's web page, there's only info about fixing the tr4....

    I think I mentioned it in one of my posts about the video output from a +2. I too don't know why the incorrect installation of TR7 doesn't cause a problem, but I haven't spent any significant time trying to work it out.
  • edited January 2013
    Something concerning TR4...

    I'm using csync instead of composite on pin20 (and composite on pin16) of my rgb scart cable and I'm having a problem with one of my +2 grays not holding a stable picture (the other two +2 although identical board issue to the first, produce a stable picture). The tv seems to switch in and out of RGB mode, at least thats what the green sign on the tv indicates..

    Where could the problem be... on the csync or the composite signal? I've already installed TR4 the right (reversed) way... but as I said, I'm only using composite as a blanking signal (scart pin16). Could it be that the TR4 2N3904 is bad and needs replacement? Being installed the wrong way all these years, could it have died?
  • edited January 2013
    Hi Georg,

    the switching into RGB mode is made only by the signal at pin 16 of the SCART plug. It is a fast input made in the past for text signal inserting into a present TV picture for example from an external teletext converter. This pin either needs a continous voltage of more that 0.7V or a composite sync signal with an amplitude of more than 0.7V. I found one TV set (a mini color TV from Roadstar) that did not switch if a DC voltage is present but switched if a composite or a horizontal sync signal is present. All other TV sets I tested worked also using a DC voltage at pin 16. Note that the input impedance at this pin is about 75 Ohm. That means you need a current of more or equal 0.7V/75Ohm=9.3 mA at this pin.

    Greets Ingo.
  • edited January 2013
    Hi Ingo,

    yes ofcourse, pin16 is for switching between RGB and composite depending on voltage, but I was thinking that maybe if the CSync signal that I now have on pin20 (and composite on pin16) wasn't strong enough, then I could be getting the same behaviour.
    Actually the TV switches from a clear RGB picture to horizontaly warped (but with right colour and brightness) picture and back like once a second.

    Since I don't have composite on pin20 (but Csync) i imagined that if the tv was actually switching to composite, instead of the warped picture I shouldn't be getting any picture at all ...

    But it could just be the composite signal that I'm using for Blanking as you suggest.

    The weird thing is that another two identical to the first +2s (issue 3) give a stable picture to the same tv with the exact same cable...
    Maybe the (reversed) tr4 transistor is dead and needs changing?
  • edited January 2013
    gtsamour wrote: »
    Maybe the (reversed) tr4 transistor is dead and needs changing?
    Yes, maybe - you will have to test...
  • edited January 2013
    ingo wrote: »
    Yes, maybe - you will have to test...

    That will be the first think I'll try thank you....
    If this doesn't work then it must be something with CSync not being strong enough... but I find this difficult to be since there are no components between the rgb socket's corresponding pin for csync and the ULA and TEA2000 according to schematics...
  • edited January 2013
    Guys I'm buffled with something in page 6 of Ben's "Video fixes
    for all ZX Spectrum 128K models" guide which is found here.

    Either the schematic for the 2N3904 transistor is wrong (1:C 2:B 3:E) or I'm missing something... I think the transistor should be (1:E 2:B 3:C)

    It says on page 6.... "The right pin on this picture is the 12V, but in the original way the 2N3904 is mounted, the
    12V is connected to the emitter of the 2N3904: that is definately wrong" but at the same time from the picture shown above as I understand it and if the 2N3904 actually is as it is shown (C B E), the emitter is conected on 12V if the transistor is installed the "right" way which is reversed....

    Is there something mistaken in the guide?
  • edited January 2013
    I need to know how to do the audio fix for +2A.
    Which are the components (pieces) needed to do the "mod" ?
    I'd like to have a working stereo output. Thanks to all!
  • edited January 2013
    DaRkHoRaCe wrote: »
    I need to know how to do the audio fix for +2A.
    Which are the components (pieces) needed to do the "mod" ?
    I'd like to have a working stereo output. Thanks to all!

    Doing a stereo mod is fairly complicated, it means cutting tracks on the PCB and soldering on a network or resistors etc. Someone on here has done a little board that you can solder in in place of the AY chip and has the resistor network built neatly onto PCB.
    My rubbish website including the redrawn Amstrad schematics and the new home of the Sinclair FAQ wiki.
  • edited June 2013
    Just thought I would say that I have done the switching of TR4, and removed C31, and the impact on the screen stability is astounding! I thought it was an old CRT set that was making the image a little less steady, but the improvement was considerable.

    Anyone who has a +2 and is comfortable doing a bit of careful desoldering and soldering, this modification is well worth the effort.

    Thanks to all of you who have contributed these posts: they are very useful indeed!
  • edited June 2013
    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?
  • edited June 2013
    schombi wrote: »
    Do all +2 (grey) suffer from these problems and should be fixed
    Yes I think so. The orientation of the transistors is printed the false way at the PCB. The insertation of the sound carrier into the color mixer is a basic principle in the schematic of the grey +2 unfortunately.
    I own a grey +2 from Taiwan and had the same issues.

    Greets Ingo.
  • edited June 2013
    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
  • edited September 2013
    I'm not sure if this would count as a fix as such, but since it seems that many use csync or whatever on SCART pin 16 (blanking) I wanted to mention the method I'm using.

    I have moved the LK1 jumper to LK3 to get 12V on RGB pin 5. However, it turned out that the 1k resistor at R15 (and the one at R9) were missing from my machine. Fair enough, I calculated that any resistor between 225 and 825 ohms at R15 should give me between 1V and 3V on SCART pin 16. And, as it happens, these values are also fine for providing >9.5V on SCART pin 8 (for 4:3 aspect) from the same 12V source (RGB pin5). I put in a 330 ohm resistor at R15 and it's working beautifully and is within the SCART spec for both pin 8 and 16.

    Maybe you all already know this. I've had my +2 for a week and am still researching the various mods and fixes :)
  • edited September 2013
    gtsamour wrote: »
    If all three TR4, TR5 and TR7 transistors were wrongly installed in reverse by amstrad (except just tr4), why didn't anyone else mention it?
    Even at Velesoft's web page, there's only info about fixing the tr4....

    I've mentoined it before, but got the same reaction back then.
    People don't believe it ;)

    Anyway, don't forget that this is only with one of the +2 board issues; I posted some pics of another board issue (don't know the model numbers out of my head) which had the correct ori?ntation of those parts.
  • edited September 2013
    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.
    __________

    An elegant implementation example for this fix.

    Relay_Top.jpg

    Relay_Bot.jpg
    'Interface 1bis' for the Sinclair ZX Spectrum
  • edited September 2013
    9t19.jpg
  • edited October 2013
    1024MAK wrote: »
    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.

    I think I have to do this. My drive sometimes outputs weird warbling noise which obviously screws up loading. Sometimes the noise begins just by closing the drive lid, sometimes I can stop it again by tapping the drive or moving the machine around, sometimes not. It's pretty odd. I guess this mod is worth trying, unless there are better ideas?

    So basically cut the white line, insert a 100 ohm resistor? The capacitor - can I just solder it to the "white" pin on the main board and ground?
  • edited January 2014
    It's a little bit off-topic, not really spectacular and probably of no interest to those using a TV set as a display device for their Spectrum 128k +2, but I did this mod out of sheer need.
    http://www.youtube.com/watch?v=TFE_8us_k-o
    'Interface 1bis' for the Sinclair ZX Spectrum
  • edited January 2014
    Ive just finished sorting out my grey +2 by changing R38 out for the 5.5k, the sounds are nearly equal now but im getting buzzing in the background that increases as the volume is turned up, ive tried with a pair of headphones too to rule out the cable and tv, same there also. So far ive de-coupled the audio out the video signal, switched TR4 around and changed R38
  • edited January 2014
    Also I think its sort of video related, for instance, im testing this with 128k Sanxion, you can clearly hear the buzzing on the title screen but as soon as you press to start its a lot louder on the "Prepare to die", then quietens down again once the game starts.
  • edited January 2014
    This is something to do with the tape deck, it only buzzes when its connected, any ideas peeps?
  • edited January 2014
    Also, it happens with another grey +2 tape recorder ive tried in it, maybe ruling out the tape as the problem after all
  • edited January 2014
    I can't really add anything technically helpful here but I have a +2 grey with a very audible buzz. Most notable on the start up menu (tape loader, 128, 48 basic etc). Also when using the up / down keys to scroll through the menu the buzz changes pitch during the keypress. There's a thread on this issue over on amibay as well as one of the guys is looking into it.
  • edited January 2014
    Macc has started a new thread about the buzzing on the audio here...

    Mark
  • edited May 2014
    Macc wrote: »
    ...Ive just finished sorting out my grey +2 by changing R38 out for the 5.5k, the sounds are nearly equal now...

    Same here on my side. When I changed R38 I noticed no difference.:confused:

    Then I decided to do as user endangermice posted:

    "If you swap out R80 for a 330k, R45 for a 39k and R37 for 3.3k things will sound a lot better."

    And now indeed the PLAY command sounds as loud as the BEEP command.

    However, I noticed that prior to change any of the mentioned resistors, if I simply disconnected the cassette plug of the mainboard the sound would be free from some interference (from the tape player?) which was definitely audiable.

    Now, after changing the 4 resistors it pratically makes no diference having the tape player connected or disconnected. Even the occasional picture role caused by pushing the fast-forward, rewind or play buttons is gone.
    :confused:

    I was getting ready to install a on/off switch for the tape player but now it seems not to be necessary... Of course I am happy with the result but I can't help wondering what caused this side effect.
  • edited May 2014
    Dan Antohi wrote: »
    It's a little bit off-topic, not really spectacular and probably of no interest to those using a TV set as a display device for their Spectrum 128k +2, but I did this mod out of sheer need.
    http://www.youtube.com/watch?v=TFE_8us_k-o

    Actually, I find your mod rather spectacular! 8-)

    We all grew up with spectrums having internal speakers and I suppose some of us got used to hear sound coming from the inside of the machine...

    That was something I definitely missed since the days of the 128k and onwards.

    I think it suits every spectrum ever made, even if it's just for nostalgia's sake.

    BTW, what type of speaker are you using?
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