Trouble issue 6A
Posted: Sat Dec 23, 2023 8:53 am
Hi guys, I need your help!
I bought faulty Zx+, issue 6A with many problems, the voltages on the board were not correct, I did a recap, I changed TR5-defective, zenner diode-defective, changed 7805 with Traco, I also found 7 out of 8 TMS4352 defective I replaced with: KM4164 (which were double tested and in Spectrum issue 2 and with the DRAM Tester) and at some point it worked, I had the startup logo
I wanted "bual-boot" and that's where the nightmare started (according to the saying: the best is the enemy of the good!).
I suspected low-ram, I unsoldered it and double checked in another Spectrum issue 2 and it works, as well as with DRAM Tester, I changed ULA6-7 in issue A- which had ULA5-3 and it works. I tested the integrated 74LS04 with Xgecu T-48 - it's ok
I also changed the Z-80 and it works, the only one I didn't change is the PCF1306P!
If I remove it from low-ram, the image on the monitor changes, if I remove it from upper-rom, nothing changes
I have:
ic13 (and all of the other 4116 chips too)
vbb (top left): -5,17V
vdd (bottom left): +12.14V
vcc (bottom right): +4.98V
voltage regulator
input: +11.55V
output: +4.99V
I am attaching some pictures
Thank you and best regards!
I bought faulty Zx+, issue 6A with many problems, the voltages on the board were not correct, I did a recap, I changed TR5-defective, zenner diode-defective, changed 7805 with Traco, I also found 7 out of 8 TMS4352 defective I replaced with: KM4164 (which were double tested and in Spectrum issue 2 and with the DRAM Tester) and at some point it worked, I had the startup logo
I wanted "bual-boot" and that's where the nightmare started (according to the saying: the best is the enemy of the good!).
I suspected low-ram, I unsoldered it and double checked in another Spectrum issue 2 and it works, as well as with DRAM Tester, I changed ULA6-7 in issue A- which had ULA5-3 and it works. I tested the integrated 74LS04 with Xgecu T-48 - it's ok
I also changed the Z-80 and it works, the only one I didn't change is the PCF1306P!
If I remove it from low-ram, the image on the monitor changes, if I remove it from upper-rom, nothing changes
I have:
ic13 (and all of the other 4116 chips too)
vbb (top left): -5,17V
vdd (bottom left): +12.14V
vcc (bottom right): +4.98V
voltage regulator
input: +11.55V
output: +4.99V
I am attaching some pictures
Thank you and best regards!