Mark
Search found 5145 matches
- Sun May 12, 2024 3:45 pm
- Forum: Hardware
- Topic: FIXED Spectrum +2 grey RAM fault but RAM is good
- Replies: 31
- Views: 575
- Sun May 12, 2024 2:22 pm
- Forum: Hardware
- Topic: FIXED Spectrum +2 grey RAM fault but RAM is good
- Replies: 31
- Views: 575
Re: Spectrum +2 grey RAM fault but RAM is good
The joystick chip is believed to be the same as the chip in the Sinclair Interface 2. Hence it's not believed to be essential. The other thing of note, is that the data bus outputs can only drive each data line low (like open collector/open drain).
Well done on making progress
Mark
Well done on making progress
Mark
- Sat May 11, 2024 10:05 pm
- Forum: Spectrum BASIC
- Topic: New Pascalated BASIC Contest
- Replies: 4
- Views: 165
Re: New Pascalated BASIC Contest
Moved to the ZX Spectrum BASIC section, as this is a more appropriate section. I’ve left a shadow in the development section.
Mark
Mark
- Sat May 11, 2024 3:08 pm
- Forum: Hardware
- Topic: FIXED Spectrum +2 grey RAM fault but RAM is good
- Replies: 31
- Views: 575
Re: Spectrum +2 grey RAM fault but RAM is good
If the fault is or has been intermittent, poor IC socket contacts, dry jointed solder joints, and PCB track faults are still possibilities.
Mark
Mark
- Sat May 11, 2024 10:29 am
- Forum: Hardware
- Topic: ZX81 Comp. Mod, no Video
- Replies: 14
- Views: 755
Re: ZX81 Comp. Mod, no Video
The length (time) of the back porch and the trigger level have to be in the right range, otherwise it affects both line (horizontal) and field (vertical) synchronisation of the picture. If you are using a NE555, I’ve found that cheap versions from trading sites are too slow. It’s impossible to set u...
- Sat May 11, 2024 10:20 am
- Forum: Hardware
- Topic: FIXED Spectrum +2 grey RAM fault but RAM is good
- Replies: 31
- Views: 575
Re: Spectrum +2 grey RAM fault but RAM is good
Unlikely given that resistors are used to divide the data bus and the two groups of DRAM are controlled differently.
I’m wondering if the ULA is receiving all the control signals from the Z80.
Mark
I’m wondering if the ULA is receiving all the control signals from the Z80.
Mark
- Fri May 10, 2024 8:38 pm
- Forum: Hardware
- Topic: FIXED Spectrum +2 grey RAM fault but RAM is good
- Replies: 31
- Views: 575
Re: Spectrum +2 grey RAM fault but RAM is good
Yes, this is a tricky fault. You said earlier that you had changed the Z80. Did you try the removed chip in another Spectrum?
Mark
Mark
- Fri May 10, 2024 5:01 pm
- Forum: Hardware
- Topic: FIXED Spectrum +2 grey RAM fault but RAM is good
- Replies: 31
- Views: 575
Re: Spectrum +2 grey RAM fault but RAM is good
Yeah, there are replacement modules, but these are not exactly cheap. Especially if it's more of a guess as to what's wrong...
Mark
Mark
- Fri May 10, 2024 3:03 pm
- Forum: Hardware
- Topic: FIXED Spectrum +2 grey RAM fault but RAM is good
- Replies: 31
- Views: 575
Re: Spectrum +2 grey RAM fault but RAM is good
So the Z80 is likely able to write to this RAM and the ULA can read from it okay. It could be that something is causing the signal to be marginal at the Z80, or it could be that there is a strange control fault. Strange RAM faults in models that use the custom multiplexer chip (IC10, PCF1306P / ZX84...
- Fri May 10, 2024 1:52 pm
- Forum: Hardware
- Topic: FIXED Spectrum +2 grey RAM fault but RAM is good
- Replies: 31
- Views: 575
Re: Spectrum +2 grey RAM fault but RAM is good
Without context (which device is driving the data bus at any point in time) it's rather hard to make a determination just on a 'scope waveform. The most important thing is: when being driven, are the levels within the valid TTL logic level ranges? See here for logic level range details. When the bus...