ZX Spectrum Bits & Bobs Bytes
Examples of issues, screen displays etc. What the fault was and how corrected
|Date||Image||Description of fault||Fix||Spectrum version, issue etc|
|11 Nov 2018||On boot large vertical black and white stripes with random flashing green and yellow blocks||Suspected Z80 fault due to display and replacement of the Z80 fixed the issue||48K Rubber Key Issue 4B (039-318467 R)|
|14 Nov 2018||Grey scale display only. No colour||Previous work been done on Caps and LM1889N - looks very poor.
On investigating, previous work had caused damage to, or removal of several PCB tracks.
LM1889N socketed and replaced. Still no colour.
Continuity tests showed several tracks missing and 3 x patches installed to repair (Pin 2 -> point below KB1 / Pin 12 -> R42 / Pin13 -> C65 +ve [pictured]). Colour achevied with the C65 +ve to Pin 13 patch.
|48K Rubber Key Issue 3B|
|20 Nov 2018||Failure of initial tests with no -5 volt on L-RAM||Voltage Regulator, TR4 and TR5 replaced - this did not correct the missing -5v issue.
C65 part of the -5v circuit and all capacitors replaced as matter of course anyway. The -5v now working and therefore C65 was obviously at fault.
Boots and diagnostic ROM tests passed.
|48K Rubber Key Issue 3 (D01-052360 G)||11 Dec 2018||Inteference in picture with a large horizontal 'wavy' bar that moves slowly down the screen before going back to the top.||Voltage Regulator, TR4 and TR5, and capacitors already replaced. Testing with no unit top on and the issue did not show. Separately had noticed the smaller membrane tab had split into the 2 pieces. This was fixed and stuck back together. Following this and testing again with the 2 parts of the unit together, the issue did not show. I can only surmise that the exposed membrane tracks were shorting on something (modulator?)||48K Rubber Key Issue 3 (D01-052360 G)|