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TR4 or TR5?

protekprotek
edited May 2014 in Hardware
My issue two gives horizontal bars on bootup. Flicking reset takes it to copyright screen though. I measured voltages and got 4,9V, 11,99V and -4,3V. The -5V rail is bit out of threshold but was it TR4 or TR5 that needs changing?

Funny thing that if I power the Spectrum by plugging the wall wart, it'll give the bars but if I plug the power connector, it'll boot normally. My issue 3 doesn't make any difference whichever I plug.
Post edited by protek on

Comments

  • 1024MAK1024MAK
    edited May 2014
    Have the electrolytic capacitors been renewed?

    Mark
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  • balfordbalford
    edited May 2014
    I'll second Mark's suggestion - I've seen boards producing out of tolerance -5V, capacitor replacement will sort this out.

    In my experience TR4/TR5 are either 100% alive or 100% dead :)

    B
    The Spectrum Resuscitation Thread - bringing dead Spectrums back to life
    zx-diagnostics - Fixing ZX Spectrums in the 21st Century (wiki)
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  • protekprotek
    edited May 2014
    Caps I assume to be originals. Visually they look ok. Any place to source axial capacitors? My local store has only radial type.
  • balfordbalford
    edited May 2014
    I use Vishay BC axial components from Farnell. They're a little pricey but if you're going to keep the machine, they're a close enough match to the originals:

    9429258226_ddef1c9e2d_z_d.jpg

    B
    The Spectrum Resuscitation Thread - bringing dead Spectrums back to life
    zx-diagnostics - Fixing ZX Spectrums in the 21st Century (wiki)
    Sinclair FAQ Wiki
  • protekprotek
    edited May 2014
    Thanks!

    I think it might be also worth mentioning that there is a buzzing sound, when the Spectrum is powered. Is it the coil?
  • balfordbalford
    edited May 2014
    Again perfectly normal - issue 1 and 2 boards seem to have much louder coils than later machines.

    B
    The Spectrum Resuscitation Thread - bringing dead Spectrums back to life
    zx-diagnostics - Fixing ZX Spectrums in the 21st Century (wiki)
    Sinclair FAQ Wiki
  • ZornZorn
    edited May 2014
    The voltages you measured suggest TR4 & TR5 are in working order.

    The initialisation problem could be caused by a failing C27, so I agree with the advice to replace all of the electrolytic capacitors and this could well bring the -5 V supply rail back to where it should be.

    Axial electrolytic capacitors are available, but not very common now. Radial capacitors could be mounted as I demonstrate here: https://www.youtube.com/watch?v=TeCVt2T-YSo

    If the noise from the inductor is particularly annoying, giving it a thick coating of varnish or similar might help.
  • ramsrcramsrc
    edited May 2014
    Maplin also still have a reasonable range of Axial Capacitors (Surprisingly!)

    www.maplin.co.uk/search?text=axial capacitors
  • protekprotek
    edited May 2014
    Shame that Maplins doesn't ship outside UK and Ireland.
  • ramsrcramsrc
    edited May 2014
    Ooops - Sorry! I didn't notice that you were outside the UK.

    Reichelt will ship to Finland: http://www.reichelt.de

    I use them a lot, and they carry a very extensive range of components.

    To be honest, I am surprised Maplin don't ship outside of the UK. Particularly in this day and age!
  • protekprotek
    edited May 2014
    I managed to find the needed axials from a local shop. They have to order them from their supplier but there's no extra cost and I can get them next week.
  • protekprotek
    edited May 2014
    I got the axial capacitors the other day and I swapped them over. The Spectrum now seems to boot straight into copyright text without having to hit the reset button. The -5 V rail now gives -4,48 V instead of -4,3 V, so there is a slight improvement.

    Good thing I got some extras because otherwise I would've run short, if I had just ordered the ones mentioned in the 48k Service Manual.
  • pkerseypkersey
    edited May 2014
    Congratulations!
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