I bought a very cheap eBay 48K, rather battered with no guarantee and no power supply. I was originally going to convert it into a keyboard, but then a cheap power supply turned up. I booted it and other than the keyboard membrane everything worked. At this point I didn't have the heart to gut it and ordered a keyboard membrane, cleaned everything up, and booted it, all was good I could type and run basic programs. However I didn't have a mono lead to try to load games, so ordered a lead which turned up a couple of days later. Plugged everything in and switched on. However now I only got a black screen with a white border. Reading around it seemed the ram was failing the boot test. I ordered a diagnostic card which confirms my lower ram is faulty.
Where should I start investigating for failures?
Issue 4S 48K Lower RAM faulty
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1024MAK
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Re: Issue 4S 48K Lower RAM faulty
The diagnostic card/ROM should indicate which part of the memory is failing.
What did it report or show?
The lower DRAM is IC6 to IC13. Each DRAM chip supplies ONE bit in the eight bit BYTE.
Mark
What did it report or show?
The lower DRAM is IC6 to IC13. Each DRAM chip supplies ONE bit in the eight bit BYTE.
Mark
Standby alert “There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
Re: Issue 4S 48K Lower RAM faulty
This is the board I bought https://www.ebay.co.uk/itm/254449796763 ... media=COPY I need to read up more on how to use it properly. I don't currently know what the leds represent , the text on screen says lower ram is faulty and upper ram is good.
Re: Issue 4S 48K Lower RAM faulty
I had hoped the diagnostic board would arrived with some instructions. The ebay instructions say
Coloured squares
However I can't type anything to change roms as there is no display. The board appears to go through various tests during which the border changes colour. The screen shows black bars, a random selection of squares and before showing this message which says lower ram FailThis listing is for 1 x ZX Spectrum Diagnostic board, and comes loaded with 3 diagnostic ROM's (Dylan Smith's original 48k & 128k ROM v0.1, and Brendan Alford's ROM v0.38)
The Diagnostic board is built using the original design by Dylan Smith and can be updated/flashed using Dylan/Brendon flashing tool which is included on the ROM.
The diagnostic board allows functional testing of ZX Spectrum hardware and related clones. (48k, 128k +2 Grey)
(Does not work on the +2A/2B/3 models)
LED output on the diagnostic board will assist in locating faulty RAM chips on the Spectrum.
The Diagnostic board has been configured as follows:
Page 0 - Dylan's diagnostic 48k ROM v0.1
Page 4 - Flash utility
Page 5 - Brendon's diagnostic ROM v0.38
Page 6 - Dylan's diagnostic 48k ROM v0.1
Page 7 - Dylan's diagnostic 128k ROM v0.1
When page jumper 1-2 is selected the board will boot from page 0
Coloured squares
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1024MAK
- Bugaboo
- Posts: 3125
- Joined: Wed Nov 15, 2017 2:52 pm
- Location: Sunny Somerset in the U.K. in Europe
Re: Issue 4S 48K Lower RAM faulty
The web site that describes Dylan's diagnostic software (as well as the hardware) is here.
The LEDs flash in a sequence and at one point will indicate which bit in each byte is malfunctioning.
With Dylan's hardware design, a user when running it as a diagnostic device, does not get to choose which ROM image is used. The first “page” (page 0 in the ebay description) of the EEPROM/flash ROM memory chip is always used. That is set in the design of the hardware.
One jumper shunt/link selects between the ZX Spectrum ROM or the ROM on the diagnostic board. The second jumper shunt/link selects if the board should ignore or use the M1 signal from the Z80 microprocessor (it allows a user to test to see if this signal works).
The extra ROM images in the EEPROM/flash ROM memory chip can however be used by machine code. Or a suitable BASIC program that includes the necessary machine code.
The first photo does not appear to show a simple RAM error. So it could be one of the multiplexer chips, IC3 or IC4, or other problem with the address bus to the DRAM on the DRAM part of the address bus.
Mark
Edited because I remembered that this board supports the overline tags.
The LEDs flash in a sequence and at one point will indicate which bit in each byte is malfunctioning.
With Dylan's hardware design, a user when running it as a diagnostic device, does not get to choose which ROM image is used. The first “page” (page 0 in the ebay description) of the EEPROM/flash ROM memory chip is always used. That is set in the design of the hardware.
One jumper shunt/link selects between the ZX Spectrum ROM or the ROM on the diagnostic board. The second jumper shunt/link selects if the board should ignore or use the M1 signal from the Z80 microprocessor (it allows a user to test to see if this signal works).
The extra ROM images in the EEPROM/flash ROM memory chip can however be used by machine code. Or a suitable BASIC program that includes the necessary machine code.
The first photo does not appear to show a simple RAM error. So it could be one of the multiplexer chips, IC3 or IC4, or other problem with the address bus to the DRAM on the DRAM part of the address bus.
Mark
Edited because I remembered that this board supports the overline tags.
Last edited by 1024MAK on Fri May 19, 2023 7:59 pm, edited 1 time in total.
Standby alert “There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
Re: Issue 4S 48K Lower RAM faulty
Thank you Mark that link is perfect. My Google fu let me down trying to find something like this. I'll spend the evening having a good read.