Amstrad 6128 Plus 6128

[Blank_Reg]

Help me ressurect this machine - if possible!

Inherited this machine, but only brings up a white screen when turned on!

Turning it on and off a few times will sometimes bring up shades of green or even blue, but mainly a full white screen without border.

Tried a different BR + BASIC ROM cart known working and a different Z80 CPU known working.

No visible signs of cap or trace failure.

Any suggestions or is this typical of an ASIC failure?

Many thanks.

[d_kef]

I don't know if it is ASIC failure but as a first step you can try the Diagnostics ROM. If you are lucky it's just the RAM and the diags ROM will give you a clear indication unless a data or address line has been shorted by the failing IC.
You can download the Diagnostics ROM here 
Install the AmstradDiagLower.rom as a lowet ROM in your M4, plug it in and power up your Plus (optionally cross your fingers).

d_kef 

[Blank_Reg]

Nice one - brilliant! Will try that. I have a Centronics to edge converter as well. Lowest ROM, so like position 1? 

[Blank_Reg]

So dig out a CPC 6128, connect M4, set up WIFi, upload diagnostic ROM in position 1, shutdown, move to 6128 plus, boot with M4, see what it says yeah?

[Blank_Reg]

I have a dandinator too with Noel's diagnostic ROM - does this work on a plus system? Version 1.2L I believe.

[d_kef]

You can use any ROM position. Typically 31. Then enable lower ROM at position 31 in the M4 ROM menu.
You can also use the dandanator, but I can't give you any extra information as I have never used one. 

d_kef

[Blank_Reg]

Understood. Will try that then when I have a moment and report back. Many thanks.

[Blank_Reg]

Tried the Dandinator - even the reset didn't work! Mind you, it doesn't work on my other Amstrad plus either (though things like MF2 seem to work)

The behaviour seems to mimic strongly what happens if you don't insert a cart and switch on (single colour blank screen). Had the cart riser out, cleaned and replaced it - no change.

Left on of a bit, the Z80 gets warm - about 45-50C. Same for the FDC and the ASIC. The RAM and other misc controller clips are cooler at 30C I'd say.

Noticeable though is the AY38912/P sound chip. It's getting quite warm, maybe 60-70C which seems odd given it's not processing any sound...

[Blank_Reg]

The fact I get a colour and not a black screen / no power suggests it's recoverable doesn't it, if it's just down to a failed transistor, capacitor? If the ASIC dies it's usually a black screen / no power?

[Blank_Reg]

I understand there's no project in train either to reproduce the old 40489 ASIC either yet?

[Bryce]

The fact I get a colour and not a black screen / no power suggests it's recoverable doesn't it, if it's just down to a failed transistor, capacitor? If the ASIC dies it's usually a black screen / no power?

No, the ASIC sends a 12 bit signal (4 bits for each base colour) to a 3x 4bit DAC (AMS 48464 - Digital to analogue converter). Even with a dead ASIC, the DAC will convert whatever random voltages are appearing on the ASIC pins into analogue values that the screen will then display. It would only show black if all 12 ASIC pins were at 0V, and even on a dead ASIC, this is unlikely (unless the ASIC has exploded and it's contents are spread around the inside of the case).

Bryce.

[eto]

Just to be sure: When you attach the Dandanator you still have a known working cartridge in the slot?

(The Plus will not work without cartridge, even if the ROM is attached externally)

[Blank_Reg]

The fact I get a colour and not a black screen / no power suggests it's recoverable doesn't it, if it's just down to a failed transistor, capacitor? If the ASIC dies it's usually a black screen / no power?

No, the ASIC sends a 12 bit signal (4 bits for each base colour) to a 3x 4bit DAC (AMS 48464 - Digital to analogue converter). Even with a dead ASIC, the DAC will convert whatever random voltages are appearing on the ASIC pins into analogue values that the screen will then display. It would only show black if all 12 ASIC pins were at 0V, and even on a dead ASIC, this is unlikely (unless the ASIC has exploded and it's contents are spread around the inside of the case).

Bryce.

Maybe this is why I get random colours, usually white, but sometimes green, orange, light purple each time I turn it on.

I have a UNI-T voltage tester. Which of the tiny pins coming out of the ASIC should I test to see if any are going to 0v so at least then I'll know it's the ASIC that's faulty?

[Blank_Reg]

Just to be sure: When you attach the Dandanator you still have a known working cartridge in the slot?

(The Plus will not work without cartridge, even if the ROM is attached externally)

Yes the BR / BASIC cart is indeed inserted. It's a dandinator mini if that is relevant - I know there are other types about. Even on a working plus system it ignores everything to do with it, even reset.

[dragon]

The dandanator works without a plus catridge?.

Not, why?. Because dandanator needs the plus have enabled the access to the RAM.

In other worlds needs that the acid chip comunication with the asic works.

A computer that made the same with a catridge and without  a catridge and nothing changes sound to me a ram don't enabled.


First question is working the comunication between acid-Asic? check continuity between all the pins in the  amstrad acid and asic.

Second question is working the chip hc/ls between the Zilog and seed? Because its a patch chip to fix a bug in the asic acess to the catridge pages.

Try in the catridge the Gerard test to ram, thats don't write  nothing in the screen only  change colours in border and paper.

https://www.cpcwiki.eu/forum/amstrad-cpc-hardware/quick-and-dirty-ram-test-for-cpc/msg106676/#msg106676


You catridge is original or is a catridge using the hack to the acid asic?.

[Bryce]

The fact I get a colour and not a black screen / no power suggests it's recoverable doesn't it, if it's just down to a failed transistor, capacitor? If the ASIC dies it's usually a black screen / no power?

No, the ASIC sends a 12 bit signal (4 bits for each base colour) to a 3x 4bit DAC (AMS 48464 - Digital to analogue converter). Even with a dead ASIC, the DAC will convert whatever random voltages are appearing on the ASIC pins into analogue values that the screen will then display. It would only show black if all 12 ASIC pins were at 0V, and even on a dead ASIC, this is unlikely (unless the ASIC has exploded and it's contents are spread around the inside of the case).

Bryce.

Maybe this is why I get random colours, usually white, but sometimes green, orange, light purple each time I turn it on.

I have a UNI-T voltage tester. Which of the tiny pins coming out of the ASIC should I test to see if any are going to 0v so at least then I'll know it's the ASIC that's faulty?

On the ASIC:
Red = Pins 113, 114, 115, 116
Green = Pins 109, 110, 111, 112
Blue = Pins 104, 105, 106, 107

Or on the AMS48464:
Red = Pins 5, 4, 3, 2
Green = Pins 9, 8, 7, 6
Blue = Pins  14, 13, 12, 11

Bryce.

[Blank_Reg]

Cheers. Off to Glastonbury this week but will run through these pin checks when I get back.

[Blank_Reg]

The fact I get a colour and not a black screen / no power suggests it's recoverable doesn't it, if it's just down to a failed transistor, capacitor? If the ASIC dies it's usually a black screen / no power?

No, the ASIC sends a 12 bit signal (4 bits for each base colour) to a 3x 4bit DAC (AMS 48464 - Digital to analogue converter). Even with a dead ASIC, the DAC will convert whatever random voltages are appearing on the ASIC pins into analogue values that the screen will then display. It would only show black if all 12 ASIC pins were at 0V, and even on a dead ASIC, this is unlikely (unless the ASIC has exploded and it's contents are spread around the inside of the case).

Bryce.

Maybe this is why I get random colours, usually white, but sometimes green, orange, light purple each time I turn it on.

I have a UNI-T voltage tester. Which of the tiny pins coming out of the ASIC should I test to see if any are going to 0v so at least then I'll know it's the ASIC that's faulty?

On the ASIC:
Red = Pins 113, 114, 115, 116
Green = Pins 109, 110, 111, 112
Blue = Pins 104, 105, 106, 107

Or on the AMS48464:
Red = Pins 5, 4, 3, 2
Green = Pins 9, 8, 7, 6
Blue = Pins  14, 13, 12, 11

Bryce.

"AMS48464"

Do you mean the 40464 chip?

[Bryce]

The fact I get a colour and not a black screen / no power suggests it's recoverable doesn't it, if it's just down to a failed transistor, capacitor? If the ASIC dies it's usually a black screen / no power?

No, the ASIC sends a 12 bit signal (4 bits for each base colour) to a 3x 4bit DAC (AMS 48464 - Digital to analogue converter). Even with a dead ASIC, the DAC will convert whatever random voltages are appearing on the ASIC pins into analogue values that the screen will then display. It would only show black if all 12 ASIC pins were at 0V, and even on a dead ASIC, this is unlikely (unless the ASIC has exploded and it's contents are spread around the inside of the case).

Bryce.

Maybe this is why I get random colours, usually white, but sometimes green, orange, light purple each time I turn it on.

I have a UNI-T voltage tester. Which of the tiny pins coming out of the ASIC should I test to see if any are going to 0v so at least then I'll know it's the ASIC that's faulty?

On the ASIC:
Red = Pins 113, 114, 115, 116
Green = Pins 109, 110, 111, 112
Blue = Pins 104, 105, 106, 107

Or on the AMS48464:
Red = Pins 5, 4, 3, 2
Green = Pins 9, 8, 7, 6
Blue = Pins  14, 13, 12, 11

Bryce.

"AMS48464"

Do you mean the 40464 chip?

Yes. Typo.

Bryce.

[Blank_Reg]

Finally done the check: Results

ASIC
104 - 2v
105 - 2.2v
106 - 2.2v
107 - 2.2v
109 - 2.2v
110 - 2.2v
111 - 2.2v
112 - 2.2v
113 - 2.2v
114 - 2.2v
115 - 2.2v
116 - 5v

40464
5 - 2.8v
6 - 2.8v
7 - 2.8v
8 - 2.8v
9 - 2.8v
11 - 0.2v
12 - 0.2v
13 - 0.2v
14 - 0.2v

Screen shows white with no border. Oddly it changed colour to blue then back to white whilst touching each pin in turn on the 40464.
I redid them again after about 5 mins and the 2.8v pins on the 40464 had all dropped to 2.1v, and the 0.2v pins had all increased to 1v. On the ASIC, the 2.2v had dropped to between 1.6v and 1.8v as the unit got warmer. Pin 116 remained constant at 5v. All chips were warm except the RAM and the disc I/O related ones. The hottest was the AY sound chip.

[Bryce]

What test equipment do you have?

Bryce.

[Blank_Reg]

I fear I have no oscilloscope! Could you recommend one? The Zoyi ZT-703S seems a good price / performance balance.

[Bryce]

I fear I have no oscilloscope! Could you recommend one? The Zoyi ZT-703S seems a good price / performance balance.

The Zoyi ZT-703S is actually surprising good for the price. According to the reviews I've seen, it seems to be relatively well built, doesn't have any serious malfunctions (ie: give dodgy measurements), etc. However, as with many devices at this price level, the bandwidth is majorly exaggerated. You can trust the scope readings up to maybe 20 or 25MHz, but not up to the 50 that it claims. But that's completely ok for fixing a retro computer, when you really only want to check clock presence or valid data.
I'd still like to mention, that you should only invest your money in this scope if you intend to do more electronics in the future and build your skills. For the computer you are currently trying to repair, it will most likely just confirm that the ASIC is dead and the money would be better spent on a replacement 6128.

Bryce.

[Blank_Reg]

Er, yes I know

[Gryzor]

The Amstrad 6128 Plus is a classic 8-bit home computer known for its robust performance and vibrant graphics. It comes with a built-in disk drive and 128KB of RAM, making it a powerful machine for its time. The Amstrad 6128 Plus 6128 model remains a beloved piece of computing history among retro enthusiasts. Its versatility and functionality set it apart in the vintage computer market.

Just a spammer...