ZX 48k Spectrum Display Problem

[keitha]

Hi

Does anyone know what the problem with this ZX is?


image upload

 

[ptp170]

This might prove useful http://hardware.speccy.org/reparar-i.html

 

[protek]

You might want to measure voltages for the +5, -5 and +12 Volts pins on all the lower RAM chips. That'll give you pointers where to start looking for the probable cause.

 

[Bryce]

As the Spectrum 48K tend to only have 3 extrememly common problems:

1 - Power circuitry - Check voltages as Protek suggests. If they are wrong then you need to swap 2 transistors.
2 - Lower RAM - Most likely your issue in this case - Replace lower RAM.
3 - ULA dead - Pretty unlikely.

Bryce.

 

[keitha]

Found awesome videos; explaining everything Think I'll need to watch it a few times before it sinks in.

https://www.youtube.com/watch?v=TeCVt2T-YSo

Ps; Are the cheapo 9v ebay type PS adaptors ok to use with the Sinclair?

 

[protek]

If it's a switching PSU pushing at least 1,5 Amps, you should be ok.

 

[keitha]

If it's a switching PSU pushing at least 1,5 Amps, you should be ok.

Thanks

http://www.ebay.co.uk/itm/390797206312?_trksid=p2060353.m1438.l2649&ssPageName=STRK:MEBIDX:IT

 

[protek]

If it's a switching PSU pushing at least 1,5 Amps, you should be ok.

Thanks

http://www.ebay.co.uk/itm/390797206312?_trksid=p2060353.m1438.l2649&ssPageName=STRK:MEBIDX:IT

You don't want that one. That one has positive center. You want one with negative center or switchable polarity.

 

[keitha]

Right! Didn't realise that. Is this the right type:

http://www.ebay.co.uk/itm/UK-AC-DC-...721?pt=LH_DefaultDomain_3&hash=item2ec4a5b8e1

 

[ptp170]

 

[keitha]

If it's a switching PSU pushing at least 1,5 Amps, you should be ok.

Thanks

http://www.ebay.co.uk/itm/390797206312?_trksid=p2060353.m1438.l2649&ssPageName=STRK:MEBIDX:IT

You don't want that one. That one has positive center. You want one with negative center or switchable polarity.

Thank you for keeping me right

- - - Updated - - -

Appreciated

- - - Updated - - -

As the Spectrum 48K tend to only have 3 extrememly common problems:

1 - Power circuitry - Check voltages as Protek suggests. If they are wrong then you need to swap 2 transistors.
2 - Lower RAM - Most likely your issue in this case - Replace lower RAM.
3 - ULA dead - Pretty unlikely.

Bryce.

Thanks

 

[roy_bates]

im curious.

why do you need a power supply if you managed to power it up to take that picture.

did you borrow the supply from another system?


im here if you never manage to find the problem.
could be cpu,rom,or memory,or combination of a couple of things.including a power problem.

 

[keitha]

im curious.

why do you need a power supply if you managed to power it up to take that picture.

did you borrow the supply from another system?


im here if you never manage to find the problem.
could be cpu,rom,or memory,or combination of a couple of things.including a power problem.

My Sinclair PS is failing apart, and thought I'd ask about compatible replacements (glad I did)

Appreciate the offer