Well doneXorA wrote:Found it, got confused with the SMD caps and fitted C97 with a 10uF, replaced with the 1nF and I have the magic K
Another ZX80 lives
Discussion forums for users of the Sinclair range of computers - ZX80, ZX81, ZX Spectrum, their clones and Cambridge Z88
About the ZX80 / ZX81
Which version of the ZX80 Core is this? PokeMon's first version V1.0, or his V1.1?poglad wrote:I've done some more checking - with the ROM chip removed. In the various switch positions, with J100 connected in the right position, I've found that pin 27 /WE is high all the time, while pin 1 A14 toggles between low and floating in various positions. A13 and A12 toggle between low and high as I would expect.
If I connect J100 the other way (against the advice of the user guide), I can get /WE to go low sometimes. So I think those two pins are definitely the root of my troubles, and will look on the schematic and try to understand what's up.
The ROM (EEPROM) only drives the data bus (when selected by /OE and /CE both low). All other pins on an EEPROM are inputs only.poglad wrote:Oh - slowly understanding the schematic - it would be correct for those two to float without the ROM chip in. They would be either +5V or whatever the pin was connected to.
I am pretty sure it is like described. Put J100 to the left position will give GND (over resistor) to /WR and this can be override through ROM switch in position 4-7 or C-F. On the right side you have the /WR signal at the EEPROM which should allow to write to the EEPROM (for programming) but this can be override with ROM switch too to write protect the EEPROM in position 4-7 and C-F. So this was meant to connect choose a ROM image when using the 32k or 64k EPROM (27C256 or 27C512).poglad wrote: If I connect J100 the other way (against the advice of the user guide), I can get /WE to go low sometimes. So I think those two pins are definitely the root of my troubles, and will look on the schematic and try to understand what's up.
1 x UM1233„IC99“ (ASTEC modulator UM1233, alternative chinch socket, print version)
1 x L9933uH/0,9R (only together with switched regulator IC97)1 x X1SFE 6.5 (ZF filter, 6.5 MHz, 3 pin, e.g. MURATA)
1 x ZX80Keyboard (ZX80 membrane keyboard, listed at sellmyretro.com)(alternative: 40 SMD tactile switches Alps SKQGAFE010, 0.98N, Farnell or RS-Comp.)
(alternative: 40 SMD tactile switches Schurter LSG 1301.xx)
1 x mini heatsink TO220 (for variant b with 74LS types and linear regulator)
1 x M3x8screw with nut (variant c)
1 x power supply 9V DC, 500mA, with audio jack 3.5mm
1 x cable 3-5 meter with 3.5mm audio jack, mono (!), alternative stereo with mono adapter on both ends
I'm getting there. I'm holding off any further investigations until I've fitted the new filter/resonator and the ZX81 ROM.PokeMon wrote: Anyway it would be good to get into the schematics for better understanding.