Spectrum 48K Issue 2 - "RAM 0 FAIL"
Spectrum 48K Issue 2 - "RAM 0 FAIL"
Hello,
I am testing a Spectrum 48K Issue 2 using the "ZX External ROM" sold by MyRetroStore. The ROM is loaded with four diagnostic tools, two of them being "Retroleum DiagROM v1.56" and "Brendan Alford Diagnostics 0.36D".
Before removing IC25 and IC26, Retroleum DiagROM was reporting IC25 and IC26 as suspected faulty. I have removed these two ICs then run the diagnostic tool again - now the Retroleum reports the lower 16K RAM OK, and no upper detected (or "Upper RAM error encountered), which is expected.
The other diagnostic tool, "Brendan Alford Diagnostics", shows RAM 0 FAIL (see the picture below)
I have already removed the IC6 RAM chip and tested it with using the Retro Chip Tester Pro. Like the two 74LS157 ICs (IC25 and IC26), this 4116 was reported as GOOD.
Is it worth it to remove and test the remaining seven RAM chips, or shall I look somewhere else to identify the root cause of the problem?
I am testing a Spectrum 48K Issue 2 using the "ZX External ROM" sold by MyRetroStore. The ROM is loaded with four diagnostic tools, two of them being "Retroleum DiagROM v1.56" and "Brendan Alford Diagnostics 0.36D".
Before removing IC25 and IC26, Retroleum DiagROM was reporting IC25 and IC26 as suspected faulty. I have removed these two ICs then run the diagnostic tool again - now the Retroleum reports the lower 16K RAM OK, and no upper detected (or "Upper RAM error encountered), which is expected.
The other diagnostic tool, "Brendan Alford Diagnostics", shows RAM 0 FAIL (see the picture below)
I have already removed the IC6 RAM chip and tested it with using the Retro Chip Tester Pro. Like the two 74LS157 ICs (IC25 and IC26), this 4116 was reported as GOOD.
Is it worth it to remove and test the remaining seven RAM chips, or shall I look somewhere else to identify the root cause of the problem?
Valentin
- 1024MAK
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Re: Spectrum 48K Issue 2 - "RAM 0 FAIL"
Err, the screen shot you have posted shows a fault with the DRAM providing bits 1, 2, 3, 4, 5, 6, and 7.
With IC25 and IC26 not fitted, but with the ‘upper’ RAM chips still present, they will still respond when the Z80A address any address above 32768, but as they are not being supplied with the address from the Z80A (due to IC25 and IC26 missing), the address they use will be incorrect, as their address inputs are floating.
If you want to correctly disable the ‘upper’ RAM, have a read of what I said elsewhere:
To test the ‘upper’ RAM operate the switch to the open position.
All diagnostic ROMs use a machine code program to test the various addresses of each DRAM chip, and depending on what data is read back, they try to work out what the problem may be. But there is more than one possible cause, so they may sometimes produce misleading results. DRAM chips can fail in various ways. LS TTL logic chips, such as the 74LS157 (74LS257, 74HCT257) multiplexer chips (used for IC25 and IC26) are less complex and are generally speaking, more reliable. Yes, occasionally one will fail.
Mark
With IC25 and IC26 not fitted, but with the ‘upper’ RAM chips still present, they will still respond when the Z80A address any address above 32768, but as they are not being supplied with the address from the Z80A (due to IC25 and IC26 missing), the address they use will be incorrect, as their address inputs are floating.
If you want to correctly disable the ‘upper’ RAM, have a read of what I said elsewhere:
I wrote that assuming the user did not have a diagnostic ROM available. The same principles apply when using a diagnostic ROM, if the switch is made (or you don’t use a switch), the diagnostic ROM should report that the ‘upper’ RAM is not fitted or all of the ‘upper’ RAM is faulty (bits 0 through 7). Or it may report that the machine is a 16K version.1024MAK wrote: To disable the "upper" 32k of RAM, take a piece of wire and connect pin 5 on IC23 (a 74LS32) to +5V. (link).
I suggest you make a temporary solder connection with an SPST on/off switch in series. Start with the switch set to on. Then if you get to the copyright screen and BASIC works, after that, you can turn the switch off so that some simple BASIC commands can access and therefore test the upper RAM.
This is done because the ROM code tries to see how much RAM there is at start-up. After this, the BASIC ROM will ignore any RAM that is not present (or in this case, is disabled)(well, unless you reset the limits using CLEAR n). But the BASIC POKE and PEEK commands have no limits and work across the whole Z80 address range.
Double and triple check that you have the correct pin on the correct chip, or you WILL damage something. This temporary modification will disable the "upper" RAM (when the switch is ON), as the CAS signal won't reach the RAM chips.
Note that if a faulty DRAM IC is jamming one of the data lines, this won't really help.
To test the ‘upper’ RAM operate the switch to the open position.
All diagnostic ROMs use a machine code program to test the various addresses of each DRAM chip, and depending on what data is read back, they try to work out what the problem may be. But there is more than one possible cause, so they may sometimes produce misleading results. DRAM chips can fail in various ways. LS TTL logic chips, such as the 74LS157 (74LS257, 74HCT257) multiplexer chips (used for IC25 and IC26) are less complex and are generally speaking, more reliable. Yes, occasionally one will fail.
Mark
ZX81 Variations
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ZX81 Chip Pin-outs
ZX81 Video Transistor Amp
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 being good this year.
Re: Spectrum 48K Issue 2 - "RAM 0 FAIL"
Thanks, Mark.
In my previous message, I have incorrectly assumed that RAM 0 FAIL refers to the first RAM chip of the lower RAM., whereas there is no "zero" in the error message.
I followed your instructions and disabled the upper RAM. Now, when using the Retroleum DiagROM, I consistently get the expected output:
"Lower 16KB RAM: OK
No upper RAM detected!"
I have also used another testing tool on the ZX External ROM - "Sinclair ZX Spectrum System Test ROM" by Dr. Ian Logan, and, for the "RAM TEST", the message is:
"This Spectrum has 16K of memory in working order"
As for the "Brendan Alford Diagnostics" tool, this still shows the same "RAM FAIL" in my earlier screen-shot. Is it safe to assume that one of the 8x 4116 chips may be "faulty but not completely faulty"?...
In my previous message, I have incorrectly assumed that RAM 0 FAIL refers to the first RAM chip of the lower RAM., whereas there is no "zero" in the error message.
I followed your instructions and disabled the upper RAM. Now, when using the Retroleum DiagROM, I consistently get the expected output:
"Lower 16KB RAM: OK
No upper RAM detected!"
I have also used another testing tool on the ZX External ROM - "Sinclair ZX Spectrum System Test ROM" by Dr. Ian Logan, and, for the "RAM TEST", the message is:
"This Spectrum has 16K of memory in working order"
As for the "Brendan Alford Diagnostics" tool, this still shows the same "RAM FAIL" in my earlier screen-shot. Is it safe to assume that one of the 8x 4116 chips may be "faulty but not completely faulty"?...
Valentin
- 1024MAK
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- Joined: Mon Sep 26, 2011 10:56 am
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Re: Spectrum 48K Issue 2 - "RAM 0 FAIL"
Are you using the latest version?
See his announcement on Spectrum Computing forums here.
See his GitHub pages here
He is also a member here as well as on Spectrum Computing forums.
It’s always difficult to tell if the RAM is marginal, or there is a problem with the diagnostic/RAM test software. But I think it unlikely that seven of the DRAM chips all have the same fault.
Does it start up in BASIC? Can you write and run a short BASIC program? Is there and screen corruption?
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Amp
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 being good this year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Amp
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 being good this year.
Re: Spectrum 48K Issue 2 - "RAM 0 FAIL"
The version I'm using is not the latest (0.37), but one below (0.36D). I run the Soak Test as explained on the GitHub page:
If the 'S' key is held down when the machine is powered on, the firmware enters soak test mode (signified by a third high pitched tone immediately after the initialisation tones).
And I get the behaviour shown below:
If a lower RAM failure is detected, soak test mode is indicated by a narrow yellow border stripe at the bottom of the screen.
A failure detected during soak testing will halt testing (except where no upper memory is found working; this will be the case if testing a 16K Spectrum). Repeated tones will also sound to alert an absent operator of the failure.
There is a "narrow yellow border stripe at the bottom of the screen" in the image below.
However, the computer starts up in BASIC, and I can write and run short programs (didn't try to load anything though)..
returns 32767, so this is good.
If the 'S' key is held down when the machine is powered on, the firmware enters soak test mode (signified by a third high pitched tone immediately after the initialisation tones).
And I get the behaviour shown below:
If a lower RAM failure is detected, soak test mode is indicated by a narrow yellow border stripe at the bottom of the screen.
A failure detected during soak testing will halt testing (except where no upper memory is found working; this will be the case if testing a 16K Spectrum). Repeated tones will also sound to alert an absent operator of the failure.
There is a "narrow yellow border stripe at the bottom of the screen" in the image below.
However, the computer starts up in BASIC, and I can write and run short programs (didn't try to load anything though)..
Code: Select all
PRINT PEEK 23732 + PEEK 23733 * 256
Valentin
- 1024MAK
- Posts: 5165
- Joined: Mon Sep 26, 2011 10:56 am
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Re: Spectrum 48K Issue 2 - "RAM 0 FAIL"
I would say that the “lower” DRAM is working okay if it starts up and runs BASIC programs without any problems.
You may want to contact Brendan and ask him about these results.
By the way, which ULA version do you have in this board?
Sinclair discovered that the original design was marginal on the DRAM timings, hence in later boards, the timing for the “lower” DRAM was changed slightly.
Mark
You may want to contact Brendan and ask him about these results.
By the way, which ULA version do you have in this board?
Sinclair discovered that the original design was marginal on the DRAM timings, hence in later boards, the timing for the “lower” DRAM was changed slightly.
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Amp
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 being good this year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Amp
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 being good this year.
Re: Spectrum 48K Issue 2 - "RAM 0 FAIL"
Thanks, Mark.
The ULA version is 5C112E-3 I think (see the picture below).
Valentin
Re: Spectrum 48K Issue 2 - "RAM 0 FAIL"
Your C31 (100nf IIRC) looks gone.
Re: Spectrum 48K Issue 2 - "RAM 0 FAIL"
That's true, I noticed the black, burn ring, but I am not worried about it as it is on MIC line. I want to make sure all 48K of RAM are in working order before going to fix other smaller issues.
Valentin
Re: Spectrum 48K Issue 2 - "RAM 0 FAIL"
You might want to try another ULA, also.
I've found that suspect IC reports from Diagrom can be caused by a ULA that doesn't quite work properly.
I've found that suspect IC reports from Diagrom can be caused by a ULA that doesn't quite work properly.