Hi all, I have a boot up issue with this CPC. The white vertical lines flash on and off then the screen locks up at the photo taken. No input from keyboard.
I have some previous experience repairing spectrums and would be keen to have a go at this, any pointers appreciated
Interesting, starts to boot, so almost running. Looks like lower ROM starts but does not get to the Ready prompt, so having problems with the upper ROM. And then there are those lines.
There is a diagnostics ROM available Diag ROM (https://github.com/llopis/amstrad-diagnostics).
Thanks I have used diag ROM on a zx dandanator before. Is there an amstrad version which has this ROM preinstalled?
Quote from: deano467 on 22:13, 18 July 23Thanks I have used diag ROM on a zx dandanator before. Is there an amstrad version which has this ROM preinstalled?
Yes there is. Check ebay for a Dandanator mini. Or you can burn your own ROM and replace the onboard ROM.
But I am not convinced it will tell you much in this instance other than confirm the RAM is OK.
I had a similar issue with a 664 see 664 issue (https://www.cpcwiki.eu/forum/hardware-related/black-screen-664/25/) but the PCB was in a bad state in this instance and no vertical white lines.
I had a broken track between IC205 and IC212 on the Disk Controller side of the PCB.
IC205 PIN 2 AND gate input was floating high, should have been held low by IC212 PIN 5.
IC205 PIN 1 AND gate input is connected to A15
IC203 PIN 3 AND gate output is connected to ROMDIS
Every time A15 went high, the ROM was disabled.
So lower ROM worked, upper ROM was disabled. Took me a while...
Note these are 664 IC numbers
This CPC itself is in excellent condition, looks like it has been stored in a dry location. Think I'll recap then do a finger test for hot chips at the weekend.
Quote from: deano467 on 23:07, 18 July 23This CPC itself is in excellent condition, looks like it has been stored in a dry location. Think I'll recap then do a finger test for hot chips at the weekend.
Not had any cap issues with a CPC so far.
I would expect that a RAM IC of the first RAM bank is malfunctioning. Not to a degree that it halts the whole computer but based on the vertical lines and their colour I would say that D5out is always high.
The CPC will be able to boot to a point where a value read from RAM will lead to a crash.
The easiest way to check if it's really RAM, you can also force the CPC to boot from the secondary RAM bank by removing the PAL chip and replacing it with a socket, where a few pins are connected: https://hackaday.io/project/170949-amstrad-cpc-6128-halmem-tester
Quote from: Rabs on 23:34, 18 July 23Quote from: deano467 on 23:07, 18 July 23This CPC itself is in excellent condition, looks like it has been stored in a dry location. Think I'll recap then do a finger test for hot chips at the weekend.
Not had any cap issues with a CPC so far.
Is there a reset capacitor on the 6128? I know from speccys replacing a failing reset capacitor can get them to boot up correctly.
Quote from: eto on 11:36, 19 July 23I would expect that a RAM IC of the first RAM bank is malfunctioning. Not to a degree that it halts the whole computer but based on the vertical lines and their colour I would say that D5out is always high.
The CPC will be able to boot to a point where a value read from RAM will lead to a crash.
The easiest way to check if it's really RAM, you can also force the CPC to boot from the secondary RAM bank by removing the PAL chip and replacing it with a socket, where a few pins are connected: https://hackaday.io/project/170949-amstrad-cpc-6128-halmem-tester
The thing that confuses me is the text. No vertical lines.
Quote from: Rabs on 12:12, 19 July 23The thing that confuses me is the text. No vertical lines.
AH! true... that pretty much invalids my assumption. :doh:
But on the "v" of the (v3) there are indeed stripes. As it's basically impossible that it's during output due to the other characters having no stripes, it must be during write?!
Quote from: deano467 on 20:55, 18 July 23The white vertical lines flash on and off then the screen locks up at the photo taken.
Is your screenshot the final version? Looks like it's taken while there is still active screen output. If the boot sequence halts it usually stops after the full line is visible. Is it always identical or do you see slightly different output (with more or less vertical lines inside of the text e.g.) after a reset
Quote from: eto on 12:32, 19 July 23Quote from: Rabs on 12:12, 19 July 23The thing that confuses me is the text. No vertical lines.
AH! true... that pretty much invalids my assumption. :doh:
But on the "v" of the (v3) there are indeed stripes. As it's basically impossible that it's during output due to the other characters having no stripes, it must be during write?!
Quote from: deano467 on 20:55, 18 July 23The white vertical lines flash on and off then the screen locks up at the photo taken.
Is your screenshot the final version? Looks like it's taken while there is still active screen output. If the boot sequence halts it usually stops after the full line is visible. Is it always identical or do you see slightly different output (with more or less vertical lines inside of the text e.g.) after a reset
The screenshot was final version, the lines flashed on and off every second or so then settled with them showing in the photo. I will do more testing and checks at weekend and report back
Quote from: eto on 12:32, 19 July 23But on the "v" of the (v3) there are indeed stripes. As it's basically impossible that it's during output due to the other characters having no stripes, it must be during write?!
Could it be a lower ROM corruption? The Diag ROM would prove this.
I've had a chance to have another look at this. The blue vertical lines come on immediately and flash on and off every half a second or so, eventually stop flashing.
This is what I have done today. Cleaned the switch with contact cleaner thoroughly. It's working 100%.
Removed dust from board. Resoldered DC socket joints
Checked voltages at memory chips and getting 5.07V.
The right hand side bank of memory chips feel warmer than the left side.
The z80 and ROM chips are cool. The HAL chip feels warm and the chip under heatsink is hot but I guess that's why it has a heatsink.
Any other voltage checks I can do to narrow cause. Unfortunately I don't have an oscilloscope.
Finally a little bit of life... got a message about overflow in 12497, and it responds to keyboard entry with garbled character
That's weird. So the lower ROM is running, sort of, the CRTC is being setup, and maybe even the PIO and AY. Don't understand the vertical stripes and why the text is ok.
If this was me, I would run the Diag ROM next and see what the status of RAM and ROM is.
Quote from: Rabs on 08:36, 23 July 23That's weird. So the lower ROM is running, sort of, the CRTC is being setup, and maybe even the PIO and AY. Don't understand the vertical stripes and why the text is ok.
If this was me, I would run the Diag ROM next and see what the status of RAM and ROM is.
Thanks. Was thinking instead of spending £45 on a dandanator, I could replace the 40015 ROM with one of these in photo. I could have it programmed to switch between the Parados ROM and the diag ROM. When switched to the diag ROM at least it can test the ram. Does this sound reasonable?
Quote from: Rabs on 08:36, 23 July 23If this was me, I would run the Diag ROM next and see what the status of RAM and ROM is.
When running the Diagnostics from LowerROm can it still verify the original firmware?
Quote from: deano467 on 09:57, 23 July 23I could replace the 40015 ROM with one of these in photo.
Instead of that thing in the photo, you can also just replace it with a self burned EPROM and select between e.g. Amstrad daignostics and the Fimrware/Basic: https://www.cpcwiki.eu/index.php/DualOS
Quote from: eto on 12:18, 23 July 23Quote from: Rabs on 08:36, 23 July 23If this was me, I would run the Diag ROM next and see what the status of RAM and ROM is.
When running the Diagnostics from LowerROm can it still verify the original firmware?
I guess you can only check the Lower ROM if you run the Diag ROM from an external ROM board (i.e. using the Dandanator).
DiagROM.png
That would be fine if I had an eprom programmer but I don't. The guy selling that is a respected retro spare parts seller, and his switchable device only costs £7.99... much cheaper than any other source I can find.
Quote from: deano467 on 09:57, 23 July 23Quote from: Rabs on 08:36, 23 July 23That's weird. So the lower ROM is running, sort of, the CRTC is being setup, and maybe even the PIO and AY. Don't understand the vertical stripes and why the text is ok.
If this was me, I would run the Diag ROM next and see what the status of RAM and ROM is.
Thanks. Was thinking instead of spending £45 on a dandanator, I could replace the 40015 ROM with one of these in photo. I could have it programmed to switch between the Parados ROM and the diag ROM. When switched to the diag ROM at least it can test the ram. Does this sound reasonable?
I have never used the ROM module you listed. I normally just burn my own EPROM. But I also use the Dandanator. There are pros and cons with both. With your own EPROM you would have to de-solder and remove the on board ROM, which is not without risk and then of course you cannot test the Lower ROM as you have just removed it. With the Dandanator, you don't have to do this but it costs a bit more and you have to have a good working edge connector. But you can use the Dandanator for games once you have the CPC working :)
Quote from: deano467 on 09:57, 23 July 23Quote from: Rabs on 08:36, 23 July 23That's weird. So the lower ROM is running, sort of, the CRTC is being setup, and maybe even the PIO and AY. Don't understand the vertical stripes and why the text is ok.
If this was me, I would run the Diag ROM next and see what the status of RAM and ROM is.
Thanks. Was thinking instead of spending £45 on a dandanator, I could replace the 40015 ROM with one of these in photo. I could have it programmed to switch between the Parados ROM and the diag ROM. When switched to the diag ROM at least it can test the ram. Does this sound reasonable?
I think the BIOS and BASIC ROM is 40025. The AMSDOS ROM is 40015. See Amstrad Part Numbers (https://www.cpcwiki.eu/index.php/Amstrad_part_numbers). Not sure how the Diag ROM would work if you replaced 40015.
My guess is that one of the 74LS153's has a stuck bit on one of the CRTC outputs.
Bryce.
Quote from: Bryce on 15:15, 23 July 23My guess is that one of the 74LS153's has a stuck bit on one of the CRTC outputs.
Bryce.
wouldn't that also have the effect that the in the area of text there should be vertical stripes too?
Quote from: Bryce on 15:15, 23 July 23My guess is that one of the 74LS153's has a stuck bit on one of the CRTC outputs.
Bryce.
Hi Bryce, those 4 chips are cheap to swap out. Do you think the piggyback technique would work here to find any which are faulty? Thanks
Quote from: deano467 on 16:51, 23 July 23Quote from: Bryce on 15:15, 23 July 23My guess is that one of the 74LS153's has a stuck bit on one of the CRTC outputs.
Bryce.
Hi Bryce, those 4 chips are cheap to swap out. Do you think the piggyback technique would work here to find any which are faulty? Thanks
I'm not a fan of the piggyback technique in general, but as well as that, the technique will never work with a stuck bit. It will just cause a short and damage the chip you stuck on top.
But yes, you're right, it would most likely cause stripes through the text too. Have you tried changing the background and text colours in basic to see what the effect/error looks like then?
Bryce.
Bryce, only once was I able to get it to go to ready screen, but when I pressed keys only garbage was displayed. also managed to hear some beeps through the speaker when I pressed some keys.
There is no chance to change colours unfortunately
I purchased the dandanator and it has determined a faulty ram chip. It also loads up other games somewhat, so I am hoping that is all that is wrong here.
Quote from: deano467 on 13:25, 31 July 23I purchased the dandanator and it has determined a faulty ram chip. It also loads up other games somewhat, so I am hoping that is all that is wrong here.
Sounds promising but odd. Don't understand how anything works if one RAM IC (i.e. 1 bit on all bytes) is failing, unless it is some odd sort of failure mode.
Does the upper RAM bank test pass?
Quote from: Rabs on 17:25, 31 July 23Does the upper RAM bank test pass?
The games boot up with graphical glitches. That's as far as dandanator tests. I need to replace the faulty lower ram chip first to get it to boot further to test the upper ram
You can swap the banks. Forcing 2nd RAM bank (https://www.cpcwiki.eu/forum/amstrad-cpc-hardware/video-forcing-2nd-ram-bank-on-the-amstrad-cpc-6128/). I have never done it though.
Hi again. Just to feedback I replaced IC130 ram and I am now greeted with the correct boot screen :D .
All lower and upper ram tests now pass.
However using the dandanator it fails on the ROM test. Anybody have any ideas as the computer seems to be working well otherwise, loads games etc.
Also doing a prolonged soak test and no issues detected.
Quote from: deano467 on 11:12, 09 August 23Hi again. Just to feedback I replaced IC130 ram and I am now greeted with the correct boot screen :D .
All lower and upper ram tests now pass.
However using the dandanator it fails on the ROM test. Anybody have any ideas as the computer seems to be working well otherwise, loads games etc.
Also doing a prolonged soak test and no issues detected.
That's good. No idea why the Diagnostic upper ROM is showing as failed.
I also get an Upper Rom failed on my 6128s. Maybe there are variations of AMSDOS that have a different checksum.
Quote from: eto on 20:11, 09 August 23I also get an Upper Rom failed on my 6128s. Maybe there are variations of AMSDOS that have a different checksum.
Same checksum as mine and mine passes. There is an issue posted on github about this I think.