Search found 275 matches

by bola_dor
Mon Jun 07, 2021 6:50 pm
Forum: Hardware
Topic: 16K RAM Pack photos - please add yours
Replies: 15
Views: 4705

Re: JRS 16K RAM Pack

Lardo Boffin wrote: Sat Jun 05, 2021 11:43 am

Can you add some photos if you any please?
Later I ll take some. But I am talking about twhe main board RAM not the packs.. those are 16KB TS1500 clones
by bola_dor
Sat Jun 05, 2021 5:42 am
Forum: Hardware
Topic: 16K RAM Pack photos - please add yours
Replies: 15
Views: 4705

Re: JRS 16K RAM Pack

This is about the sixth design of ZX81 RAM pack that I have seen. Each one uses a different method or different variation of design for obtaining a -5V supply. Some use a transistor oscillator driving an inductor like the Sinclair 16k RAM pack. Some use a CMOS logic chip and capacitors to do it. So...
by bola_dor
Thu Jun 03, 2021 4:59 am
Forum: Hardware
Topic: ZX81 Troubleshooting
Replies: 8
Views: 922

Re: ZX81 Troubleshooting

How did this go?
by bola_dor
Wed Jun 02, 2021 12:00 am
Forum: Welcome Area
Topic: Hello from OR
Replies: 3
Views: 415

Re: Hello from OR

Hi, if you use any modern player probably you'll need an amplifier between the player and the ZX81. Any speaker with headphones output will do the trick.. remember to use mono cables.. If on Android you can try https://play.google.com/store/apps/details?id=com.baltazarstudios.playzxtapes It's primar...
by bola_dor
Sat May 29, 2021 8:53 pm
Forum: Sinclair Misc
Topic: ZX81 Patent Posters
Replies: 4
Views: 637

Re: ZX81 Patent Posters

Were are you located at?
by bola_dor
Fri May 28, 2021 7:46 am
Forum: Hardware
Topic: Issue 1 ZX81, some keys not working - keyboard looks ok, also RAM packs don't work
Replies: 2
Views: 901

Re: Issue 1 ZX81, some keys not working - keyboard looks ok, also RAM packs don't work

HJKL NL is D7. wiring-terminals.png Test it using a thin insulated wire connecting the keyboard contacts in the board socket from the large one to any one in the smaller one. You should see the characters appear in the screen. D7 and RAM CS lines are one near each other in the back connector. It sur...
by bola_dor
Fri May 28, 2021 7:28 am
Forum: Hardware
Topic: Bad 12v line ISSUE 6A with only 5v RAM
Replies: 27
Views: 3222

Re: Bad 12v line ISSUE 6A with only 5v RAM

At last.. it worked!! 20210528_020223.jpg What a relief to see that copyright again 😁. I desoldered the CPU 2021-5-28 1-8-35.jpg I broke only two lines but it came of easily.. 2021-5-28 0-31-30.jpg I think I overdid it with the desoldering braid. Luckily I could fix it easily. A11 line restored... 2...
by bola_dor
Fri May 28, 2021 4:35 am
Forum: Hardware
Topic: Bad 12v line ISSUE 6A with only 5v RAM
Replies: 27
Views: 3222

Re: Bad 12v line ISSUE 6A with only 5v RAM

If the PCB track for A11 goes to a logic high (1) voltage (above 2V), then the Z80A is definitely defective. If however the PCB track for A11 stays low (less than 2V), then something else is dragging the voltage down. Mark Thas exactly what happened.. a nice 5v flat line.. Reviewing the board. A11 ...
by bola_dor
Thu May 27, 2021 12:49 am
Forum: Hardware
Topic: Bad 12v line ISSUE 6A with only 5v RAM
Replies: 27
Views: 3222

Re: Bad 12v line ISSUE 6A with only 5v RAM

If you desolder and lift pin 1 on the Z80A (for A11), or cut pin 1 in such a way that you can solder it back together again, then try to use a resistor to pull up the PCB track for A11, what does that do the the PCB track for A11? Mark How do I use a resistor to pull up the line? Like before? From ...
by bola_dor
Thu May 27, 2021 12:29 am
Forum: Hardware
Topic: Bad 12v line ISSUE 6A with only 5v RAM
Replies: 27
Views: 3222

Re: Bad 12v line ISSUE 6A with only 5v RAM

560 Ohm resistor didn't change anything.. ( I used a preset) lowering that value started to rise the base line at about 220 Ohm but not the pulses peaks (nor the oveshooting)
I'll start to desolder, carefully...