Sinclair ZX80 / ZX81 / Z88 Forums

I tried it with an Harlequin 128. With 128k-Basic and also 48K Basic it seems to work, but with "PRINT test" I receive "299793". Is this "round-function" the problem?
With "PRINT test - 1.099" I receive "299791.9" so it seems the variable "test" is correctly stored.

looks very mysterious - is it possible to try it with an other monitor or tv? The red lines are looking so perfect - much clearer than the "NEW" prompt

- random pattern - looks like (Upper-)RAM damage

In my Speccy's I have mostly switching power regulators instead of the 7805, so this will do no change. The interference fault in my case was definitely the (faulty) external power supply.

In my case it was a faulty capacitator in the (switch) power supply. I repaired it today and now everything is ok. It seems that 105° caps are not a guaranty for a long lifetime...

Today I had nearly the same problem with "crawling dots scrolling over the screen". Tested an ZX Spectrum Issue 6a PCB. But an other Speccy, wich worked fine before also shows these dots. I used an adjustable bench top power supply and after I took an other power supply every thing works fine. Seems...

Is it possible that it's a variation of the "snow effect"? http://www.zxdesign.info/dynamicRam.shtml :roll: This effect occurs if the CPU produces uncontrolled /RAS-Signals. To prevent this you can pull /MREQ (Pin19) of the CPU high. I think a resistor <1Kohm or a wire from pin 28 (RFSHL) to +5V (pi...

Hallo Chris, mit meinen Englischkenntnissen stoße ich nun leider an meine Grenzen - da Du ja in Deutschland lebst, verstehst Du es ja evtl., wenn ich in deutsch schreibe: bei dem Fehlerbild tippe ich auf eine Schwingungsstörung die sich da am Videoausgang zeigt, also eine überlagerte Wechselspannung...

I repaired some Speccy's and often found that there where faults with sockets. Often PCB wires where shortened under the sockets or broken. Best is to test all connections of the sockets ...

Also possible is interference in the 12V power line - check C41 (100µF) an C23 (22µF). But 'cause I never owned an +2 I'm not sure...