If the fault is or has been intermittent, poor IC socket contacts, dry jointed solder joints, and PCB track faults are still possibilities.
Mark
Search found 5142 matches
- Sat May 11, 2024 3:08 pm
- Forum: Hardware
- Topic: Spectrum +2 grey RAM fault but RAM is good
- Replies: 25
- Views: 363
- Sat May 11, 2024 10:29 am
- Forum: Hardware
- Topic: ZX81 Comp. Mod, no Video
- Replies: 14
- Views: 554
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: Spectrum +2 grey RAM fault but RAM is good
- Replies: 25
- Views: 363
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: Spectrum +2 grey RAM fault but RAM is good
- Replies: 25
- Views: 363
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: Spectrum +2 grey RAM fault but RAM is good
- Replies: 25
- Views: 363
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: Spectrum +2 grey RAM fault but RAM is good
- Replies: 25
- Views: 363
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: Spectrum +2 grey RAM fault but RAM is good
- Replies: 25
- Views: 363
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...
- Fri May 10, 2024 11:42 am
- Forum: Hardware
- Topic: Spectrum +2 grey RAM fault but RAM is good
- Replies: 25
- Views: 363
Re: Spectrum +2 grey RAM fault but RAM is good
There are still two groups of eight DRAM chips. Each group provides 64K bytes. The group IC25 to IC32 is the "lower" RAM as far as the ULA is concerned. The other group of DRAM is the "upper" DRAM.
This is the reason why half of the RAM is contended and half is non-contended.
Mark
This is the reason why half of the RAM is contended and half is non-contended.
Mark
- Fri May 10, 2024 11:01 am
- Forum: Hardware
- Topic: Spectrum +2 grey RAM fault but RAM is good
- Replies: 25
- Views: 363
Re: Spectrum +2 grey RAM fault but RAM is good
Is there, at any point any screen corruption? RAM in positions IC25 to IC32 provides the RAM for the screen display. If IC31 / bit 1 was faulty, or there was an open circuit fault in the D1 data line, you will get screen corruption. Did you test to both pin 2 and 14? The other hints maybe that the D...
- Fri May 10, 2024 10:51 am
- Forum: Sinclair Misc
- Topic: Donate for this Forum, please..
- Replies: 30
- Views: 8283
Re: Donate for this Forum, please..
I must be cursed. I used the new donation link, put in the amount and got "Transaction could not be completed at this time" error. I'll try again this weekend. As it’s the same PayPal account as before (2022), I used the PayPay app and typed in the email address, it confirmed that it’s registered t...