Issue 2 issue (...)

edited November 2013 in Hardware
Just acquired an issue 2 Spectrum 48 K, selled as working board, not working keyboard. Before testing it with a psu I opened the case and discovered that the transistor mounted on the fly (TR6 ?) on z80 has a broken leg (that on z80 side facing the ula) just at the transistor plastic case, so it seems quit impossible to fix it with a soldering : (
Presuming that the TR6 (ZTX313) in not easy replaceable, may I trust page 4.3 of Service Manual that, related to ula 5c112 timing problems, speaks about of a diode (IN 4148 ) and of a resistor (4K7) alternatively used to TR6 ?
What happens if I don't fix the connection ?


Thanks !!!!!
Post edited by Cignale on
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Comments

  • edited July 2010
    Cignale wrote: »
    What happens if I don't fix the connection ?
    The purpose of the patch is to pull the ULA pin IORQGE high (=invalid) as long as the A0 line is high. Apparently the transistor is used to complete the address decoder for the ULA (=keyboard+border) which normally should act when IORQ and A0 being both low (IN 254, OUT 254). I think it is safe to see what happens by just trying, maybe the read-key routine (which occurs every interrupt, 1/50th sec) gets out of control.
    My notes say that the transistor is a regular in issue3 models and only called TR6 there. I have no recollection of such job, don't know why I made that note. I think, without checking(!), that most npn transistors would do the job.
  • edited July 2010
    What happens if you replace the old type ULA found on an issue 2 boards (5c112) with the later one? Is then TR6 necessary in this case too?
  • edited July 2010
    I have backwardly noticed this board mount a 6c001 ula....
    So maybe the collector terminal has been purposely interrupted ?

    But why, if so, emitter and base are still connected ? :-?
  • edited July 2010
    My (early) edition of Dickens' Hardware Manual says "....first batch of ULAs (had) an error in the design......some later batches of the ULA appear to have a totally different bug. A small transistor is soldered across the Z80.....". I always have understood this in such way that ULA5 needed the added 'dead cockroach' chip (in both Issues 1 and 2), and that ULA6 needs the transistor. Which transistor was added as a patch in Issue2 and made permanent in Issue3. But I never checked this believe against reality. Cignale's post now confirms my opinion.
    I would assume that the transistor leg got broken when the Z80 was temporarely removed, and wonder what that might indicate, i.c. prepare for a thorough check after replacement....
  • edited July 2010
    .... I have noticed in the other issue 2 board acquired in the same batch, is mounted an 5c112 ula and.... the z80 presents no TR6 ! There are only remnants of soldering of transistor pin....:???:
    And on this board a terminal of resistor mounted on the board on the fly at pin 11 of z80 has been disconnected; and there is no trace of 4.7 uF electrolytic with positive end to TR5 emitter (positive end of C34) and negative
    end to TR5 base (to R58 ) - one of the mods on issue 1 and 2 boards made to improve life of TR4.
    I'm quite puzzled.
    I begin to wonder if there has been a wrong swapping in the past of the 2 ulas on these issue 2 boards....:???:

    @ Roko - the Service Manual says:

    "5C102. This ULA has a timing fault which was cured by connecting
    a 74LSOO 1C mounted on a miniature board and spider. This ULA
    was fitted to approximately 40,000 units.

    5C112. This improved ULA has no spider modification, but has
    either a diode or resistor or transistor connected to it. The
    details are:
    Diode/resistor mod : 4k7 resistor from +12V to pin 30 on IC2 and
    diode (IN 4148 ) from pin 30 of IC2 to pin 33 of IC1.
    Transistor mod : TR6 (ZTX313) connected as follows:
    Base to IC2, pin 30.
    Emitter to IC1, pin 33.
    Collector to IC2, pin 11.

    6C001 This ULA alters the timing of the colour burst signal, and
    improves the performance of the Spectrum with certain television
    sets (e.g. Hitachi, Grundig) . It also causes the screen picture
    to be shifted by one character width to the left."

    So it seems that 6C001 don't need TR6 patch, am I wrong ?
  • edited July 2010
    .... I have noticed in the other issue 2 board acquired in the same batch, is mounted an 5c112 ula and.... the z80 presents no TR6 ! There are only remnants of soldering of transistor pin....:???:
    And on this board a terminal of resistor mounted on the board on the fly at pin 11 of z80 has been disconnected; and there is no trace of 4.7 uF electrolytic with positive end to TR5 emitter (positive end of C34) and negative
    end to TR5 base (to R58 ) - one of the mods on issue 1 and 2 boards made to improve life of TR4.
    I'm quite puzzled.
    I begin to wonder if there has been a wrong swapping in the past of the 2 ( socketed) ulas on these issue 2 boards....:???:

    @ roko - the Service maual says:

    "5C102. This ULA has a timing fault which was cured by connecting
    a 74LSOO 1C mounted on a miniature board and spider. This ULA
    was fitted to approximately 40,000 units.

    5C112. This improved ULA has no spider modification, but has
    either a diode or resistor or transistor connected to it. The
    details are:
    Diode/resistor mod : 4k7 resistor from +12V to pin 30 on IC2 and
    diode (IN 4148 ) from pin 30 of IC2 to pin 33 of IC1.
    Transistor mod : TR6 (ZTX313) connected as follows:
    Base to IC2, pin 30.
    Emitter to IC1, pin 33.
    Collector to IC2, pin 11.

    6C001 This ULA alters the timing of the colour burst signal, and
    improves the performance of the Spectrum with certain television
    sets (e.g. Hitachi, Grundig) . It also causes the screen picture
    to be shifted by one character width to the left."

    So imho it seems that 6C001 ula don't need TR6 patch. Am I wrong ?

    PS: @ gtsamour and roko : thanks !!!!
  • edited July 2010
    I quickly checked Issue4 diagram, where without doubt ULA 6C001 or later(!!) is used, and TR6 is present there. This transistor is connected exactly like the patch described for Issue2. Which then IMHO means that the TR6 'solution' should not be seen as a patch for the ULA but as a patch for certain boards i.c. the Issue2.
    I also checked the photos in 'my Dickens' which show a 5C112E ULA with transistor patch. My conclusion is that when 5C112 in an Issue2 can be replaced by a 6C001, the transistor patch (which is mounted on the Z80) should still be used.
    Now everytime I read "connect IC(x) pin(y) to +12V" (instead of+5V) I do a second check. IC2 is the Z80, and pin 30 is the A0 line. I see no reason for using +12V there, the 'intermediary' resistor offers no safety at all. Check!!
    The logic gate that is created by the 'simple patch' does function exactly as the transistor, I would prefer the latter though.
  • edited July 2010
    ...and what about the other issue 2 board with the 5c112 ula, but without TR6, and resistor to z80 pin 11 disconnected ? I understand that I have to mount surely tr6 to z80, but why that resistor terminal has been disconnected ?:-o
    Have I to resolder its terminal to the large pcb track between ic2 pin 11 and ic 23 ?!

    ftp://ftp.worldofspectrum.org/pub/sinclair/technical-docs/ZXSpectrumIssue2-PCB_Top.jpg

    Thanks, thanks again and sorry for bogging...
  • edited July 2010
    I think that someone was doing some experiments that should result in a repair, but was caught in the act. The best you can IMHO do is return to the original situation and then search for the original problem: a clinical approach. Your purchase seems to show a lot of despair of the previous owner, don't let that contaminate your thinking....
    and resistor to z80 pin 11 disconnected
    I think this resistor will be the 4k7 one (yellow/purple/red) you described under '5C112', as it is positioned between +5V (large track) and A0 (Z80 p11) where should not be unless a diode is provided (going to ULA pin33, IORQGE) that transports this logic Hi in order to make undecoding of I/O <>254 complete. (IOQGE should only go low when A0 is low). BTW: indeed not 12V but 5V!!

    Edit: Yes I did it: thinking twice!
  • edited July 2010
    @ roko -

    I posted on Flickr 2 photos of the board with 6C001 ula:

    the first depicts the z80 with broken collector terminal (TR6) and the (brown black red gold, and not as that You suggested ) resistor connected, while the second depicts the electr. capac patch.

    http://farm5.static.flickr.com/4087/4837584979_93d12e0a3a.jpg

    http://farm5.static.flickr.com/4150/4837584997_5e212851d0.jpg


    Thanks for the third time : )
  • edited July 2010
    Just a quick tip: if you have a transistor soldered across the Z80, and at any point you replace that Z80 and/or place a socket for it, solder that transistor back between that socket.

    That way you can swap out Z80 without further touching that transistor mod (if you decide to leave it in, that is).

    I suppose the same goes for a transistor or resistor/diode combo across the ULA, but usually it's in a socket that's a bit more difficult to solder extra things to.
  • edited July 2010
    Thanks for the advice, Retrotechie :)
  • edited July 2010
    I was intrigued by the modification where a resistor is placed between the Z80's A0 line and +12V. Indeed the repair guide (page 4.5) says 12V, where I think +5V should be the max on a Z80 pin.... Someone else shine a light here?
    Then my eye fell on an Issue2 board with ULA 6C001E-6 which board had no patch! A board of which I was not aware that it lived in my house.... I only got it working after a good cleaning(!) of anonym soldering work on chip sockets and then tested my idea about the I/O 254 issue by:
    10 PRINT AT 0,0;IN 254
    12 PRINT AT 2,0;IN 253
    20 GOTO 10
    Only IN 254 changes with key presses, IN 253 stays 255 all the time.
    Then added the resistor/diode patch using 5V instead(!) of 12V, R=3K9, just for noticing that nothing changes by that! I removed the patch and declared the board 100% working....
    The PCB says 8311 SRC095, the 32K RAMS are KM4164, the 'Link' is connected with 0V, and no other mods could be found.
    @Cignale: The resistor is 1K, which is rather heavy for such patch. So it must be the remains of an experiment. The purpose of the (black) capacitor seems to add some 'decoupling', should not change the workings.
  • edited July 2010
    Thanks, roko.
    The beforementioned resistor (1 k), apart the fact that has a terminal disconnected on a board (that with 5c112 ula) is the same on all the 2 issue board acquired, so it seems not an experiment but a regular component.
    l'm tempted to try to power up the 2 board without any fix, any great risk for this ?
    Thanks.
  • edited July 2010
    Don't know if this helps, its a pic of my original Issue2 with no mods or repairs other than being upgraded to 48k.

    http://i432.photobucket.com/albums/qq45/FrankT4/issue2b.jpg
    WIP Tritone Demo
    No more html on dropbox. :(
  • edited July 2010
    Thanks FrankT !
    Same 1 k resistor, same transistor on z80, same cap on r59, as one of my issue 2 boards, but what is that small pcb on left side of z80 ?! Is it maybe the patch for the older than Your's ula version ? Or is related to 48 k upgrade ?
  • edited July 2010
    Cignale wrote: »
    Thanks FrankT !
    Same 1 k resistor, same transistor on z80, same cap on r59, as one of my issue 2 boards, but what is that small pcb on left side of z80 ?! Is it maybe the patch for the older than Your's ula version ? Or is related to 48 k upgrade ?
    Its part of the FOXX 48k upgrade kit.
    FOXX.jpg
    WIP Tritone Demo
    No more html on dropbox. :(
  • edited July 2010
    !
    FOXX Upgrade kit, I did't know it, my fault :)

    Thanks !
  • edited July 2010
    FrankT wrote: »
    Don't know if this helps, its a pic of my original Issue2 with no mods or repairs other than being upgraded to 48k.

    http://i432.photobucket.com/albums/qq45/FrankT4/issue2b.jpg

    Weird, the black electrolytic capacitor on the upper right corner of the board does not seem to be in any other issue 2 board photo i've seen...
    Does anyone know the purpose, value and polarity of this capacitor since its not visible in the photo?

    Also the C54 cap isn't installed (right lower corner just above the speaker). I've seen issue 2 boards that have it and other ones that don't.... why?
  • edited July 2010
    From service manual:

    1.3 Modifications - Issue 1 Board
    A number of modifications were introduced, and these should be checked
    for and, if necessary, introduced retrospectively:

    ( omissis)

    (g) This modification is required for efficient operation of certain
    machine code software and should be implemented on all units. It
    has been implemented in manufacture for all ULAs 5C112-2 and
    later.
    D14 replaced by C67 (100 pF)
    R24 changed from 3k3 to Ik
    R27 changed from 680 n to 470 n
    R73 ( I k ) added between Id/32 and +5V >>

    > WHAT IS ID32 ?!
    ( h ) A significant cause of problems has been found to be failure of
    the internal power supply transistor TR4. The circuit may be
    improved by changing the value of R60 from 100 n to 270 fl and
    connecting a 4.7 uF electrolytic (perferably radial type) with <
    <<<
    positive end to TR5 emitter (positive end of C34) and negative
    end to TR5 base (to R58 ).
    4.4

    1.4 Modifications - Issue 2 Board

    A number of modifications have also been introduced for the Issue 2
    board. These should be checked and, if necessary, introduced
    retrospectively.
    (a) These components should be changed if colour quality needs
    upgrading:
    R48 changed from 4k7 to 2k2
    R49 changed from 18 k to 8k2
    R50 changed from 8k2 to 4k7
    R72 changed from 47 k (or 18 k) to 10 k
    C65 changed from 100 yF to 22 yF
    (b) Early Issue 2 boards were manufactured using a considerable
    number of 47 yF and 100 uF disc capacitors. C41 (47 nF) and C43
    (100 nF) should be replaced with axial components to prevent
    undue risk of short circuits.
    (c) To prevent l i f t i ng of the keyboard template, a thin strip (6 mm
    wide) of double-sided tape was introduced to the top edge of the
    template. (Previously, only the other 3 edges had tape). This
    modification should be introduced whenever template l i f t i n g is
    found to be a problem.
    (d) See Items 1.3(g) and (h) above <
    <<<<

    Just a note :are there ocr errors or am I wrong.....?
  • edited July 2010
    Nice picture FrankT, thanks, really should be archived! Your patch allows expansion of Issue2 with OKI chips instead of the usual TI brand. Hope your nails survived when taking it out....

    @Cignale: I checked my board for traces of the 1K resistor, there might have been one once, but I can't tell. I checked however that the resistor comes between +5V and pin 32 of ULA, which is CLocK, which means that it helps adjusting TR3.
    In the Service Manual it is mentioned under 1.3.g as R73 (page 4.4, Issue1) and the validity for Issue2 can be found under 1.4.d (page 4.5). I think that a good board will come to life with and without patches, the most (and only) urgent requirement is that the 3 voltages (-5,5,12) are present as any absence here might damage the 4116 RAMs while staring at them....

    Slightly off topic but usefull for evaluating the consistency of the Service Manual dated 1985: When I glanced through these pages my eye fell on item 1.3.c (page 4.4) where Thorn EMI states that on Issue1 boards the RAS line (output of ULA!) should be connected by means of an 1K resistor to 23V. Okay, we all get desperate some times and want to get rid off old gear, but where should we find that voltage on an Issue1 PCB? Anyone around who did upgrade in that way during the past 26 years?
  • edited July 2010
    "....Thorn EMI states that on Issue1 boards the RAS line (output of ULA!) should be connected by means of an 1K resistor to 23V. Okay, we all get desperate some times and want to get rid off old gear, but where should we find that voltage on an Issue1 PCB? Anyone around who did upgrade in that way during the past 26 years?"


    LOL :lol:

    PS: Thanks !!!
    PPS: and so "Id32" in ..."OCRese" stands for IC1 32, I suppose......
  • edited July 2010
    My answer crossed your question....
    A quick reply: YES, there appear to be OCR errors on your side. (is your copy from WOS?)
    R24 should not be IK, but 1K
    R27 should not be 470 n but 470 Ohm (the omega sign)
    And maybe more, I need to check.

    What was readable anyway: described are mods in retrospection, which means that they so to speak are improvements, and not necessarily repairs.
  • edited July 2010
    Well, in near future I'll try the 2 boards, along with a DK troniks keyboard just arrived from UK....... and after, hoping they are operational, I'll try to (re-)apply the patches described in this thread.
  • edited July 2010
    The (minor) OCR errors are in the Service Manual version found on WOS.
    The 23V advice is however present in my clear paper copy, like the advice to use a perferably radial type of electrolytic capacitor. The perforation should preferably performed in front of preoccupied perceivers. I think.
  • edited July 2010
    Lol !!!
  • edited November 2013
    Hijacking this old thread. I got hold of a (working) Issue two, which has the "real" spider-mod with the small PCB and wires from ULA to CPU fitted. Until I saw this one, I was always under the impression that the transistor on top of an Issue two CPU is the spider-mod, but then I read the service manual again and apparently I have one of the 40.000 ever produced. Just because of curiosity, how rare is a spider-mod compared to a grey-keyed Issue one Spectrum?

    I took a picture: 1c7c1be773-Spider-mod.jpg
  • edited November 2013
    Not that common, although I managed to pick one up this summer:

    9429258226_ddef1c9e2d_z.jpg

    Serial 001-017330.

    B
    The Spectrum Resuscitation Thread - bringing dead Spectrums back to life
    zx-diagnostics - Fixing ZX Spectrums in the 21st Century (wiki)
    Sinclair FAQ Wiki
  • edited November 2013
    Nice - yours seems to be older; lower serial and disc capacitors.

    Mine is 001-028846.
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