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General Category => Technical Support => Hardware related => Topic started by: Audronic on 03:46, 04 February 20

Title: Problem CPC6128 Fixed Thanks to all who Contributed.
Post by: Audronic on 03:46, 04 February 20
Hi all

I have a small problem I was wondering if you could point me in the right direction.

I have a CPC6128 that gives me the following screens:-

Boot
Geralds Memtest Original,
Geralds Memtest NEW (wip)

The Links are in LK1 and LK2 ? I get "Isp 128K  etc" ? ?
No Basic 1.1 or Ready, or cursor ?

On my other machines with the Links as above I get "AWA 128k etc"

It has been in storage for 20 Years.

When first turned on "Nothing on screen"

I have Replaced IC 108 - CRT C with a New HD6845SP
and Fitted a Good Turned socket I have tried 2 of these.

Can you give me some help Please

Thanks.  Ray
Title: Re: Problem CPC6128
Post by: Audronic on 07:43, 04 February 20
Hi All

Partial success.
Replaced the 8255.
The machine ID is now Awa.
Geralds Original RamTest now works.
Geralds Ramtest (wip) stalls ?

Still no Cursor

See photos

Ray
Title: Re: Problem CPC6128
Post by: Audronic on 07:49, 04 February 20
Photo below after 5 Tries to get passed SECURITY CHECK
Title: Re: Problem CPC6128
Post by: SOS on 09:34, 04 February 20
Hmmm, i'm not a hardware-guy,
but an similar (?) effect i have seen often, when i do strange things with the ROM's.
Could you connect an ROM-Board and burn 2 ROM's with an booting message (like MAXAM)?
One with an ROM-Number > 7 and one with an ROM-Number < 7?
Do you see both ROM-Booting Messages?
Title: Re: Problem CPC6128
Post by: llopis on 09:49, 04 February 20
Yeah, my first guess would be a faulty BASIC ROM. Try replacing it with something else or connecting some kind of external ROM and see if that works.
Title: Re: Problem CPC6128
Post by: Bryce on 10:56, 04 February 20
My experience from many, many repairs: This is usually due to a bad AMSDOS ROM, not the BASIC ROM. In the few cases where swapping the AMSDOS ROM didn't help, it turned out to be an issue with the FDC.

Bryce.
Title: Re: Problem CPC6128
Post by: Audronic on 11:10, 04 February 20
Hi Bryce, Sos, llopis

Thanks I will have a look at those areas.

I have just found a problem with the /cas line on IC 119 - Ic 125. Out with the snippers.

I will have a look tomorrow  its 8:12 Pm now over here

Thanks

Ray
Title: Re: Problem CPC6128
Post by: Audronic on 00:33, 05 February 20
Hi All


Is there a document that outlines the order in which the CPC6128 starts up.
as to what is tested, initialised etc. this would help with diagnosis of an unwell machine


If there is something please post a link or the name of the document


Thanks.  Ray
Title: Re: Problem CPC6128
Post by: Audronic on 04:55, 05 February 20
Hi All

Update

Changed the ROM 40015 (Bryce Warned me) Did NOT fix the Problem
But I now have a Fault indicated with Geralds Ramtest (WIP).
But which chip/s ?


EDITED
 
Ray
Title: Re: Problem CPC6128
Post by: Audronic on 07:23, 05 February 20
Hi All
Update Again !


Changed some Ram in 2nd bank, now Geralds RamTest (wip) has worked.
Still not Booting, No Ready - Cursor.


Ray
Title: Re: Problem CPC6128
Post by: SOS on 07:41, 05 February 20
does the AMSDOS loaded correctly?
=> do you see both ROM-Messages (e.g. MAXAM on ROM9 and MAXAM on ROM 5), when connecting an external ROM-Board?
Title: Re: Problem CPC6128
Post by: Audronic on 08:04, 05 February 20
@SOS 

AMSDOS does not fully load.
I have tried Dandanator,Just goes to startup screen.
I have used lower rom for the 2 RamTests by Gerald.

I plug in my Xmem-X-mas and I get as per photo Starts to boot and stops after |RPM.

Thanks for your thoughts.

This is the 8th (EIGHTH) time I have tried to send a photo Grrrr Security check Hmmmn
on the 9th time I was able to send the photo ? ? ?


Ray
Title: Re: Problem CPC6128
Post by: GUNHED on 10:32, 05 February 20
Still looks like a bad ROM. Try to replace connected ROMs - one by one if possible.
Title: Re: Problem CPC6128
Post by: Bryce on 11:02, 05 February 20
Still looks like a bad ROM. Try to replace connected ROMs - one by one if possible.

But it didn't start even with zero external ROMs attached. My guess is that something in the floppy circuitry is bad. Try disabling the entire floppy hardware and see if it boots.

Bryce.
Title: Re: Problem CPC6128
Post by: GUNHED on 12:05, 05 February 20
But it didn't start even with zero external ROMs attached. My guess is that something in the floppy circuitry is bad. Try disabling the entire floppy hardware and see if it boots.

Bryce.


Exactly, the problem is in the ROM. Since the OS seems to work, take a look at the BASIC ROM.
Title: Re: Problem CPC6128
Post by: Bryce on 12:45, 05 February 20
Possible I suppose, but unlikely. ROMs tend to break in terms of rows or columns, or bits stuck on the address or databus. Any of these failures would stop the CPC from getting as far as it does at the moment.

Bryce.
Title: Re: Problem CPC6128
Post by: Audronic on 14:42, 05 February 20
Hi All


Thanks.
I will change over the 40015 FDD Rom IC 204 tomorrow and see what happens

TYPO Should read 40025 Grrrr.

Ray

Title: Re: Problem CPC6128
Post by: Bryce on 14:44, 05 February 20
I thought you already changed it? At least you stated you did just above??

Hi All

Update

Changed the ROM 40015 (Bryce Warned me) Did NOT fix the Problem
But I now have a Fault indicated with Geralds Ramtest (WIP).


If the AMSDOS ROM hasn't been changed yet, then that is definitely the first thing to try.

Bryce.
Title: Re: Problem CPC6128
Post by: GUNHED on 23:08, 05 February 20
Another idea, probably unlikely... can it be a weak PSU? With them this issue could happen.
Title: Re: Problem CPC6128
Post by: Audronic on 00:58, 06 February 20

If the AMSDOS ROM hasn't been changed yet, then that is definitely the first thing to try.

Bryce.


Bryce sorry I made a TYPO I have removed only the 40025  (ROM-PC3) IC103

Thanks

 I am about to remove the 40015 and test the motherboard without the 40015 ?




Thanks.  Ray
Title: Re: Problem CPC6128
Post by: Audronic on 01:01, 06 February 20
Another idea, probably unlikely... can it be a weak PSU? With them this issue could happen.


Thanks  Have used a good known power supply (2  different Power Supplies) Both around 5.04 Volts with a 4 amp capacity.
I think the power supply is not the problem


Ray
Title: Re: Problem CPC6128
Post by: Audronic on 01:48, 06 February 20
Hi All


Nearly there 40015 Removed, Powered up and got this Yeahhh


Ray
Title: Re: Problem CPC6128
Post by: Audronic on 02:35, 06 February 20
Hi All


No Success back to NO Ready- NO Cursor after replacing 40015 , Now it gets hard to find the fault.


Ray
Title: Re: Problem CPC6128
Post by: SOS on 07:51, 06 February 20
When you remove the AMSDOS 40015-IC and burn an AMSDOS.ROM on Slot 6 on your ROM-Board and e.g. MAXAM on Slot 5.
What happens?
Hung the ROM6 (you dont see Booting-Messages from ROM's with Number < 6?) ?
Can you access the floppy?
Title: Re: Problem CPC6128
Post by: Audronic on 08:24, 06 February 20
Hi SOS


No The machine CanNot Boot to a ready or cursor.


I am working around the Floppy drive circuit at the moment.


I have found an 74HC240 that is unwell.
Am about to replace this. ( I think I have done this on an other machine ?)


I don't know about Maxam  I will have a look at what it does ?


Ray

Title: Re: Problem CPC6128
Post by: Audronic on 08:51, 06 February 20
Hi All

Ok after replacing the 74HC240 IC203
The machine now boots  Phewww
BUT I have phantom keyboard input on the machine.
If I boot with my xmem attached I go straight into SOS's Yancc on the second restart But its working
I will look at the keyboard input tomorrow

Interesting project

Thanks to all who offered assistance

Ray
Title: Re: Problem CPC6128
Post by: Bryce on 09:49, 06 February 20
Cool. So, if it also gives those phantom keys when the keyboard isn't attached, then it's either the AY or IC101 (74LS145). The AY is the most likely candidate as they are much more prone to failing.

Bryce.
 
Title: Re: Problem CPC6128
Post by: TotO on 10:01, 06 February 20
I got the "96RUN ..." text displayed when my AY "BC2 pin" was not connected to VCC... But, I think that can be another problem around that.
Title: Re: Problem CPC6128
Post by: Audronic on 11:00, 06 February 20
@Bryce (https://www.cpcwiki.eu/forum/index.php?action=profile;u=225) @TotO (https://www.cpcwiki.eu/forum/index.php?action=profile;u=290)

Yes no keyboard attached.

Thanks I am cutting out the AY as the emails arrived.
I will power it up soon without the AY then fit a socket and try again.


Thanks All


Ray
 
Title: Re: Problem CPC6128
Post by: Audronic on 11:15, 06 February 20
Hi All


Interesting with the AY removed I get on the screen :-


63RUN". Then drops down a line and backspaces the cursor to the normal position


Ray
Title: Re: Problem CPC6128
Post by: Bryce on 11:41, 06 February 20
That might be just due to floating inputs on the 8255, but if it still does that with a new AY installed, then the 8255 is bad.

Bryce.
Title: Re: Problem CPC6128
Post by: Audronic on 02:14, 07 February 20
Hi All

Nearly there ?

Normal Boot screen, Keyboard input NOT WELL.
Ok So on with the saga. The next victim will be IC101 74ls145 Keyboard decoder.
Where did I put those snippers.

Ray
Title: Re: Problem CPC6128 RESOLVED thanks
Post by: Audronic on 07:43, 07 February 20
Hi All

Fixed

Ran out of Ay3-8912 (NOT A), only had an AY3-8912A so on this Motherboard Z70290 there is provision (Holes for a socket)
 for some 9 pin 2.2k Resistor Arrays (A222J) pullups , Fitted.
Keyboard works. no double characters.
I was unable to get the Dandanator to work Grrrrr
Had a broken track (trace) near the 50 Way expansion connector.
It turned out to be the /RD (Pin32) line. Replaced with appropriate wire Now OK Dandanator works.

What an interesting Sheep of Hit this project was.

Thanks to all who helped, Every comment has some merit.  Thanks

Ray
Title: Re: Problem CPC6128
Post by: Bryce on 09:26, 07 February 20
Well done. Another CPC back working.

Bryce.
Title: Re: Problem CPC6128
Post by: TotO on 12:36, 07 February 20
I have not spoke about AY /A version, because I though that you was using the original AY.  ;D
Nice to know your CPC is now working again!
Title: Re: Problem CPC6128
Post by: Bryce on 13:26, 07 February 20
I have not spoke about AY /A version, because I though that you was using the original AY.  ;D
Nice to know your CPC is now working again!

He was using the original AY, but he only had an A version as a spare when he went to swap it.

Bryce.
Title: Re: Problem CPC6128
Post by: TotO on 14:01, 07 February 20
He was using the original AY, but he only had an A version as a spare when he went to swap it.
I have understood that he got the "63RUN" issue with the original AY, because this may occur with the "A version" w/o resistor network. By the way, it is good thing to have recovered his CPC.
Title: Re: Problem CPC6128 Fixed Thanks to all who Contributed.
Post by: Audronic on 04:43, 08 February 20
Hi All

An overView of what went on:-

Amstrad CPC6128 Components Changed :-

1)   8255
2)   40025
3)   4164 (1) Ic 120
4)   40015
5)   74HC240 (FDC Circuit)
6)   AY-3-8912(A) and Resistor array

7)   74LS145 IC101. 
8)  Trace repaired /RD to 50 Way expansion connector
     Trace Repaired as Dandanator would NOT work,

NB:- Sockets were added for the I/Cs.

Test Equipment used :-

Voltmeter.
Digital Probe.
Soldering Iron & Solder.
Solder Sucker.
Schematics.

Memory Bank Change (HAL Socket).
Lower Rom board with 2 Ram Tests (Geralds)
Dandanator as a test device.
Eprom programmer to replace the 40015 and 40025.

Brains.
Good sense of Humour and Coffee.


Ray