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General Category => Amstrad CPC hardware => Topic started by: Audronic on 07:47, 03 November 15

Title: Repairs to a CPC6128
Post by: Audronic on 07:47, 03 November 15
Hi All


Part 2 of the faulty CPC's purchased.
I have a CPC 6128 which gives me the following screen.(A lot better than the 464 - gave me Nothing)
That's a Colour Monitor. Nothing gets hot, The 5 volts is good. I have not connected the 12 volts yet. NO Stuck lines on CPU. ------->

Ray






Title: Re: Repairs to a CPC6128
Post by: gerald on 08:58, 03 November 15
This screen is typical from RAM fault.
Title: Re: Repairs to a CPC6128
Post by: Bryce on 09:13, 03 November 15
Yup, I second Geralds diagnosis and a Like for the seriously cool retro scope!

Bryce.
Title: Re: Repairs to a CPC6128
Post by: Audronic on 12:36, 03 November 15
Thanks Chaps for the pointer to RAM.

For a CPC 6128 is the lower Ram 0000 to ffff 
   IC 127 - IC 134.
or IC 119 - IC126 as Pin 15 /cas?, is stuck HI on this set ??.
This is progress :-[   
Ps:-   Yep my old Cro that does a fair job, has some sync problems but -------
Ray
Title: Re: Repairs to a CPC6128
Post by: Bryce on 12:50, 03 November 15
It can only be the lower 64K of RAM, the upper RAM isn't needed for the computer to boot properly.

There's a trick involving bridging the PAL to swap the upper and lower RAM for testing purposes. It's described somewhere here on the Forum, but I can't find it, maybe someone else can point you to this?

Bryce.
Title: Re: Repairs to a CPC6128
Post by: Audronic on 10:09, 05 November 15
Thanks Bryce I found the article and made up a shunt to suit, But No Boot

Where the project is up to :-

The 40010 Gate Array is OK Swapped with an other.
The Z80 changed Still the Same.
The 40025 Rom 32K signals all look OK.
Have bypassed the Pal chip IC 118, using Bank 1 SAME problem

BUT the Memory Table below this is for Bank 0  Bank 1 is worse ?
Time to remove ALL of Bank 0.
Ray

Title: Re: Repairs to a CPC6128
Post by: arnoldemu on 10:40, 05 November 15
Bypass the PAL entirely and put the 6128 into 64KB mode.
Or is this what the bypass using the 2nd bank does?
Title: Re: Repairs to a CPC6128
Post by: Audronic on 10:54, 05 November 15
@arnoldemu (http://www.cpcwiki.eu/forum/index.php?action=profile;u=122)


The Bank 1 is worse than bank 0
The bypass was done with the help on the forum .
Need some help fixing CPC6128 not booting (http://www.cpcwiki.eu/forum/amstrad-cpc-hardware/need-some-help-fixing-cpc6128-not-booting/msg75204/#msg75204)
Amstrad CPC6128 Pal Bypass IC 118
If the main bank of ram is failing, you can switch to the second one:
You can now test Bank 1
      - remove the PAL from its socket
      - on the socket :
      - link pin  9 to pin 19 (A14 to A14out) (Eq to LK5)
      - link pin  8 to pin 12 (A15 to A15out) (Eq to LK6)
      - link pin  7 to pin 16 (NCAS to NCAS1)
      - link pin 17 to pin 20 (NCAS0 to VCC)

If your CPC boot, then either the PLD or ram bank 0 is failing.

You can now test Bank 0 by changing :-

      - link pin  9 to pin 19 (A14 to A14out) (Eq to LK5)
      - link pin  8 to pin 12 (A15 to A15out) (Eq to LK6)
      - link pin  7 to pin 17 (NCAS to NCAS0)
      - link pin 16 to pin 20 (NCAS1 to VCC)
I had some headers that i wired up as above, due to faulty ram in BOTH banks it was unable to work.

Ray
Title: Re: Repairs to a CPC6128
Post by: Bryce on 11:12, 05 November 15
Yup, looks like you may have several damaged RAMs. An entire bank swap is probably the easiest way to go.

Bryce.
Title: Re: Repairs to a CPC6128
Post by: Audronic on 06:17, 07 November 15
Hi Bryce


Yes I decided to do that, Clipped out the chips, and then i had the following thoughts :-


""  I have cut out ALL of the Memory for Bank 0 ??

Cut 128 Pins free.
Extract 128 Pins.
Clean out 128 Holes.
Solder in 8 - 16 Pin sockets, 128 Solder joints.

Are you keeping count.

We are up to 512 Transactions and this is only for BANK 0.

In Hindsight :-
I should have just removed the 5 chips marked in red and replaced them in sockets to test that the error was removed.
OR even just removed 1 Chip IC127 and re tested PIN 14.""

I have since acquired this desolderer, which saves me 128 transactions. Phew.

PS :- Still Desoldering

Ray





Title: Re: Repairs to a CPC6128
Post by: Bryce on 10:43, 07 November 15
Quote from: Audronic on 06:17, 07 November 15
Hi Bryce

Yes I decided to do that, Clipped out the chips, and then i had the following thoughts :-

""  I have cut out ALL of the Memory for Bank 0 ??

Cut 128 Pins free.
Extract 128 Pins.
Clean out 128 Holes.
Solder in 8 - 16 Pin sockets, 128 Solder joints.

Are you keeping count.

We are up to 512 Transactions and this is only for BANK 0.

In Hindsight :-
I should have just removed the 5 chips marked in red and replaced them in sockets to test that the error was removed.
OR even just removed 1 Chip IC127 and re tested PIN 14.""

I have since acquired this desolderer, which saves me 128 transactions. Phew.

PS :- Still Desoldering

Ray

I don't need to keep count, I've done this operation probably 30 to 40 times in the past. However, it's still the best solution because if 5 of them failed then the other 3 will fail too quite soon and trying to remove and replace these after you've installed a socket left and right of the broken chip is much more annoying than removing them all together in the first place.
I learnt my lesson on a Spectrum 48K lower RAM, where the ICs are as close together as you can get them (the sockets actually touch each other!) Very fiddly trying to remove one last chip from the middle of a row of sockets.

Bryce.
Title: Re: Repairs to a CPC6128
Post by: ||C|-|E|| on 15:37, 07 November 15
That repair is a great opportunity to have all the memory in nice sockets instead of soldered to the motherboard  :) . I always liked that idea  :)
Title: Re: Repairs to a CPC6128
Post by: Audronic on 03:47, 08 November 15
Yes it is good that the Ram's are now socketed..
BUT  Help Please Photo shows it all.
Not Booting completely ?
Ray

Title: Re: Repairs to a CPC6128
Post by: AMSDOS on 04:31, 08 November 15
Quote from: Audronic on 03:47, 08 November 15
Yes it is good that the Ram's are now socketed..
BUT  Help Please Photo shows it all.
Not Booting completely ?
Ray


No BASIC 1.1 by the looks of it, someone else will have a better suggestion I'd imagine.


The colours are correct though, so Firmware must be being initialised.
Title: Re: Repairs to a CPC6128
Post by: Audronic on 06:51, 08 November 15

@AMSDOS (http://www.cpcwiki.eu/forum/index.php?action=profile;u=330)
Thanks for the info on the colours.
Weird effect, if i tap the probe on or put my finger near  on Pin 1 FDC chip IC201 Z765 (Reset - FDC reset line ) it jumps to Ready
Some progress
Ray
Title: Re: Repairs to a CPC6128
Post by: radu14m on 08:23, 08 November 15
well done :)


maybe is a soldering point unstable ...check it.
Title: Re: Repairs to a CPC6128
Post by: Bryce on 15:36, 08 November 15
Suggestions:

- Dry joint somewhere on the FDC circuitry - Causing something to float?
- Dodgy capacitor?

Bryce.
Title: Re: Repairs to a CPC6128
Post by: Audronic on 22:57, 08 November 15
@radu14m (http://www.cpcwiki.eu/forum/index.php?action=profile;u=724)
@Bryce (http://www.cpcwiki.eu/forum/index.php?action=profile;u=225)
Thanks I will check for Dry Joints around the FDC area.
Another thought as i normally only use a CRO and not a Probe.
The CRO will not pickup an Open circuit (Dry Joint) on a pin it will indicate as a LO.
So i will have to use Both.

Thanks   Ray
Title: Re: Repairs to a CPC6128
Post by: Audronic on 04:44, 09 November 15
The saga continues :-

Yes a DEAD Chip (well mostly dead) IC 203 a 74HC240. The MotherBoard has been Socketed and replaced with a temporary 74LS240 (Thats all i have in the spares bin).
The machine now wakes up to the command prompt  BUT.

The Keyboard circuitry is UnWell.

Keyboard Faults ?

Not working

Y10 line ??
-=========-
Z    Nothing
X    Nothing
V    Nothing
,    Nothing
.       vx ],    That what I get on screen  ???
Spacebar    Nothing
Control
-==================-
DEL     also does not work.

Late addition :- Swapped the keyboard from a known working 6128,  Same problem. Oh well its not the Keyboard,:- Investigate.

Using the Probe has been a very useful tool.

Ray (Still smiling)
Title: Re: Repairs to a CPC6128
Post by: arnoldemu on 09:05, 09 November 15
great investigation. :)

Title: Re: Repairs to a CPC6128
Post by: Bryce on 09:35, 09 November 15
Wow, that machine really has had a hard life. At least with the keyboard problem it's a simple diagnosis. The 72LS145 has failed.

Bryce.
Title: Re: Repairs to a CPC6128
Post by: Audronic on 09:44, 09 November 15
@Bryce
You won't believe this i just finished making up a table for the IC 101 74ls145
and this is what i got :-
Pin 1 is unwell

Amstrad CPC6128  IC 101 74LS145

Decoder (Open Collector)
Pin 1 ??? ??? ?
Pin OutIN/OUTNameActivity
1OUTQ0LO - PULSE  ??? ?
2OUTQ1PULSE
3OUTQ2PULSE
4OUTQ3PULSE
5OUTQ4PULSE
6OUTQ5PULSE
7OUTQ6PULSE
8GROUNDLO
9OUTQ7PULSE
10OUTQ8PULSE
11OUTQ9PULSE
12INP3LO - PULSE
13INP2LO - PULSE
14INP1LO - PULSE
15INP0LO - PULSE
16VCC +5 VOLTSHI
Ray
Title: Re: Repairs to a CPC6128
Post by: Bryce on 10:36, 09 November 15
Yup, I did say it was an easy one :)

Bryce.
Title: Re: Repairs to a CPC6128
Post by: gerald on 10:55, 09 November 15
Quote from: Bryce on 10:36, 09 November 15
Yup, I did say it was an easy one :)

Bryce.
Note that sure.
The wrong line is driven by Q9 (pin 11)
Q0 is the line selected between two keyboard scan done at 50Hz. It is mostly low except when other lines are scanned (few ms)

Title: Re: Repairs to a CPC6128
Post by: Audronic on 22:34, 09 November 15
@gerald


Thanks for the comment, I am unclear as to what you are saying could you expand the comment Please.


Thanks   Ray
Title: Re: Repairs to a CPC6128
Post by: gerald on 22:48, 09 November 15
Quote from: Audronic on 22:34, 09 November 15
Thanks for the comment, I am unclear as to what you are saying could you expand the comment Please.
Q0 state is low most of the time in normal operation. So you cannot conclude that this pin is failing just by using the logic probe result.
Also, the keyboard errors you are seeing are related to Q9, not Q0.
- I would check that the keyboard connectors are OK (oxydation, solder)
- Check with a scope the shape of Q9 when you press a key and compare to an other working line. You will have to press a key that is controlled by that line to have valid result. Otherwise you will only see a open collector driver with no pull-up.
Title: Re: Repairs to a CPC6128
Post by: gerald on 22:56, 09 November 15
BTW, I am not saying the IC101 is fine, just that we cannot conclude from the logic probe results  ;) .
Title: Re: Repairs to a CPC6128
Post by: Audronic on 23:01, 09 November 15
@Gerald


Ok.  Thanks i will have a look with the CRO and do some comparisons.
Thanks for the update


Ray
Title: Re: Repairs to a CPC6128
Post by: Audronic on 01:42, 10 November 15
Damn  I have NO - 74LS145.
Even our local suppliers , Jaycar , Radio Parts have NIL stock
Oh well 3-4 weeks from China.
Unless any Australians know of a source ????


Thanks in anticipation    Ray
Title: Re: Repairs to a CPC6128
Post by: pelrun on 05:53, 10 November 15
http://au.rs-online.com/web/p/decoders-demultiplexers/0303624/ (http://au.rs-online.com/web/p/decoders-demultiplexers/0303624/)


2 bucks, free next-day delivery :)
Title: Re: Repairs to a CPC6128
Post by: Audronic on 09:03, 10 November 15
@pelrun

Thanks for that.
I just ordered 3.

Ray
Title: Re: Repairs to a CPC6128
Post by: Audronic on 01:54, 11 November 15
The SAGA continues


The 74LS145 arrived NEXT day form R.S, this did not cure the Keyboard problem .
Also no sound out (Del Key).


Oh well onto the AY-3-8912 (28 PIN).
Unfortunately NONE available AT R.S, Radio Parts, Jaycar.
I have some coming on a SLOW boat from china.


It could be X-MASS before i get this up and running. :-X
a Nice beginners project. :doh:


Ray (Still smilling).

Title: Re: Repairs to a CPC6128
Post by: AMSDOS on 02:41, 11 November 15
That's a shame  :(
Title: Re: Repairs to a CPC6128
Post by: ||C|-|E|| on 03:12, 11 November 15
I wonder what happened to that CPC. So many faulty chips... maybe a strong discharge when it was working? the machine has the board almost unprotected  :-X
Title: Re: Repairs to a CPC6128
Post by: Audronic on 03:28, 11 November 15
@||C|-|E|| (http://www.cpcwiki.eu/forum/index.php?action=profile;u=1447)


I purchased 2 CPC Machines KNOWING that they were faulty from a Gent in Tasmania (Just a little south from me).
I thought it might be a good Project to do some repairs on a new machine to me ( Previous TRS-80 Model 1/3/4/4p World ).
Its fine if the 6128 has a few problems I am learning heaps about them.
I am retired from paid work, this keeps the brain active.
I am having a guess that the machines have seen over voltage on the +5 volt line ??
The floppy drive is not working yet but it sort of performs, Motor runs, steps to try and find sectors,. reports errors to the screen so thats a start.
Anyway i will continue with the project.


Ray
Title: Re: Repairs to a CPC6128
Post by: ||C|-|E|| on 03:53, 11 November 15
I know, I know  :) I have followed you progress and I think that is a very nice project. When I was saying that the machine has the board unprotected I meant that Amstrad produced them that way to save costs, so if the previous owner did something wrong probably half of the chips are fried  :) .
Title: Re: Repairs to a CPC6128
Post by: Bryce on 09:14, 11 November 15
I can send you an AY, but I doubt it's the AY that's bad, because the faulty keys are in the same column not row. I'd go back and check that the connection between the keyboard membrane and the LS145 are definitely good.

Bryce.
Title: Re: Repairs to a CPC6128
Post by: gerald on 09:35, 11 November 15
Quote from: Audronic on 01:54, 11 November 15
The 74LS145 arrived NEXT day form R.S, this did not cure the Keyboard problem .
Also no sound out (Del Key).
I am with Bryce, the DEL key is also on line 9. Try the CLR key  ;)
Also beware that most chinese will sell you a AY-3-8912A which requires pull up to work on CPC.

Edit :  :doh:
Title: Re: Repairs to a CPC6128
Post by: Audronic on 11:24, 11 November 15
The Keyboard Continuity Tests

I have just tested the continuity from the following
Keyboard connectors CP 002 (left- Under) and CP001 (Right- Over)

Pins on CP002    going to IC101 74ls145
(Left)
=======================================

Near AY Chip

Pin 11 (Common Line)
Pin 12                    Pin 10
Pin 13                    Pin  9
Pin 14                    Pin  7
Pin 15                    Pin  6
Pin 16                    Pin  5
Pin 17                    Pin  4
Pin 18                    Pin  3
Pin 19                    Pin  2
Pin 20                    Pin  1

=======================================
Pins on CP001    going to IC102 AY-3-8912
(Right)
=======================================

Near AY Chip

Pin 1 (N/C)              =====
Pin 2                    Pin 14
Pin 3                    Pin 13
Pin 4                    Pin 12
Pin 5                    Pin 11
Pin 6                    Pin 10
Pin 7                    Pin  9
Pin 8                    Pin  8
Pin 9                    Pin  7
Pin 10 (N/C)             =====

=======================================
The Keyboard Matrix drawing that i am using is from the
""service.manual.464plus.6128plus "" Page 11 Key Matrix (Applies to 464 & 6128)
Is This what you requested, I have tried 2 Working keyboards -- all the same problem.

Ray
Title: Re: Repairs to a CPC6128
Post by: gerald on 11:40, 11 November 15
I don't know what my brain did these days  :picard:

All your failing keys are all on ROW 7 -> Which point to an AY problem !
Title: Re: Repairs to a CPC6128
Post by: Bryce on 12:48, 11 November 15
Is the plus and classic matrix the same? It's a Classic 6128 that he's fixing.

Bryce.
Title: Re: Repairs to a CPC6128
Post by: gerald on 14:03, 11 November 15
Quote from: Bryce on 12:48, 11 November 15
Is the plus and classic matrix the same? It's a Classic 6128 that he's fixing.

Bryce.
All matrix are the same.
But just look at the matrix table and you will  :doh: as well  ;)

hint : del z x v space , . ctrl ...
Title: Re: Repairs to a CPC6128
Post by: Bryce on 14:45, 11 November 15
Quote from: gerald on 14:03, 11 November 15
All matrix are the same.
But just look at the matrix table and you will  :doh: as well  ;)

hint : del z x v space , . ctrl ...

I saw that the other night, but that was after about 15 beers, so I still thought it pointed at the 145 for some reason.  ::)

Bryce.
Title: Re: Repairs to a CPC6128
Post by: Audronic on 23:31, 11 November 15


As there has been some comments about 2 versions of the AY-3-8912  " AY-3-8912 and AY-3-8912A "
I was just Looking at the AY Chip and took this Photo.
I was wondering if these holes could be used for the Pullup Resistors (Pack)
If so what Value Please.
Ray
Title: Re: Repairs to a CPC6128
Post by: gerald on 07:23, 12 November 15
Quote from: Audronic on 23:31, 11 November 15
I was wondering if these holes could be used for the Pullup Resistors (Pack)
Yes, these are indded for a resistor network.
Quote from: Audronic on 23:31, 11 November 15
If so what Value Please.
I would say 2.2K.
This is what is used on the Plus schematics. On CPC, this networks is not on the schematics and does not have a reference.
Title: Re: Repairs to a CPC6128
Post by: Audronic on 09:26, 12 November 15
@gerald (http://www.cpcwiki.eu/forum/index.php?action=profile;u=250)


Ok, I had a look at the CPC464+ Service Manual and the Resistor Networks (2.2k) were added.
Would that have been for greater signal stability ?.
Do we need them for the 464/6128.


Ray
Title: Re: Repairs to a CPC6128
Post by: Bryce on 09:30, 12 November 15
No it's because the non-version already has these pull-ups inside the chip. The holes are just a fallback in case they couldn't source the right version at the right price.

Bryce.
Title: Re: Repairs to a CPC6128
Post by: 1024MAK on 17:09, 12 November 15
What results do you get when measuring pin 7 of the AY sound chip?


If you simulate a key by using a suitable wire to pretend to be a key, connected directly between an appropriate output pin of the 74LS145 and pin 7 of the AY sound chip, does this produce the correct response?


Mark
Title: Re: Repairs to a CPC6128
Post by: Audronic on 23:41, 12 November 15
Hi Mark


What results do you get when measuring pin 7 of the AY sound chip?

Normally sitting HI without the Keyboard connected

If you simulate a key by using a suitable wire to pretend to be a key, connected directly between an appropriate output pin of the 74LS145 and pin 7 of the AY sound chip, does this produce the correct response?

If I simulate the letter  "a" (Pins 7 and 12)I get NO pulse on the probe  and the letter " a " On the screen

If I simulate the letter  "z" (Pins 9 and 12)I get a pulse on the probe (HI & Pulse) and NOTHING On the screen

Ray
Title: Re: Repairs to a CPC6128
Post by: Audronic on 08:09, 13 November 15
Added extra information to the Keyboard Table.


I have just tested the continuity from the following
Keyboard connectors CP 002 (left- Under) and CP001 (Right- Over)

Pins on CP002    going to IC101 74ls145    Called   Activity
(Left)                                    X? or Y?
==========================================================

Near AY Chip

Pin 11 (Common Line)                         Y10     Pulse
Pin 12                    Pin 10             Y9      Pulse
Pin 13                    Pin  9             Y8      Pulse
Pin 14                    Pin  7             Y7      Pulse
Pin 15                    Pin  6             Y6      Pulse
Pin 16                    Pin  5             Y5      Pulse
Pin 17                    Pin  4             Y4      Pulse
Pin 18                    Pin  3             Y3      Pulse
Pin 19                    Pin  2             Y2      Pulse
Pin 20                    Pin  1             Y1      LO  Pulse on the probe BUT looks just above ground on CRO.

Front of Computer
==========================================================
Pins on CP001    going to IC102 AY-3-8912
(Right)
==========================================================

Near AY Chip

Pin 1 (N/C)              =====                      O/C
Pin 2                    Pin 14             X1      HI
Pin 3                    Pin 13             X2      HI
Pin 4                    Pin 12             X3      HI
Pin 5                    Pin 11             X4      HI
Pin 6                    Pin 10             X5      HI
Pin 7                    Pin  9             X6      HI
Pin 8                    Pin  8             X7      HI
Pin 9                    Pin  7             X8      HI
Pin 10 (N/C)             =====                     O/C

Front of Computer
==========================================================
Ray
Title: Re: Repairs to a CPC6128
Post by: 1024MAK on 10:41, 13 November 15
From those results (simulation of the keys) it does look like one of the AY-3-8912 I/O pins has internal circuitry damage.


Mark
Title: Re: Repairs to a CPC6128
Post by: Audronic on 10:52, 13 November 15
HI Mark


Thanks i think that is correct, waiting some AY-3-8912's either arriving from China or Germany  I will see who gets here first.
I will now prepare the board with a new socket and Wait.
I will also put a socket strip in the place for the Resistor network just in case I am sent AY-3-8912(A).
I also have some 9 Pin 2.2k Resistor networks coming.


Ray



Title: Re: Repairs to a CPC6128
Post by: Audronic on 01:39, 28 November 15

After 2 Weeks :-------


The AY-3-8912 arrived as an AY-3-8912A From China.
Put it in and it seems to work, Keyboard OK, Del Key Beeps..
Awaiting on Proper replacement AY-3--------- and for some resistor networks (2.2k) to add to the AY-3-8912A.
Its still a work in progress, i will have a look at the Floppy drive next and associated circuitry..
What an interesting Project.

Thanks to all that helped, commented.

Ray
Title: Re: Repairs to a CPC6128
Post by: 1024MAK on 02:56, 29 November 15
Yay!  :)

Mark
Title: Re: Repairs to a CPC6128
Post by: Audronic on 09:26, 30 November 15
The Saga continues, Some Good some Not so good.

The good part is that the Floppy interface is working. Phewwww. That would be a pain to fault find
As there are no Complete Floppy drive Circuits for the Mother board. MC0020B, Z70290, 40010.


The not so good :- 1) It is looking like that the Memory Bank 1 is Unwell.
                            2) The Floppy drive does all the actions steps in and out turns the disk but won't read the disk.
                                I have not had time to look at what is wrong Yet.

I have a 3.5" drive as drive B that i have used for running some test programs, this work good.
I am able to run From Drive A, (I have borrowed another 6128) CPM 2.2 , But am unable to run CPM 2+, it look like it's trying to use some Bank 1 Memory.

Ray
Title: Re: Repairs to a CPC6128
Post by: gerald on 10:15, 30 November 15
Quote from: Audronic on 09:26, 30 November 15
The Saga continues, Some Good some Not so good.

The good part is that the Floppy interface is working. Phewwww. That would be a pain to fault find
As there are no Complete Floppy drive Circuits for the Mother board. MC0020B, Z70290, 40010.
There is  a chance that the drive section schematic in the amendment service manual (http://www.cpcwiki.eu/manuals/Amendment%20Service%20Manual.zip), in the 6128 cost down section. The same data separator is used.

Quote from: Audronic on 09:26, 30 November 15
1) It is looking like that the Memory Bank 1 is Unwell.
I've attached a memory test that covers 512k expansion RAM.
It will test the 0x4000-0x7FFF main bank and all detected expansion 16K blocks.
If the extension RAM is dead and not detected, it will only test that single block.

Quote from: Audronic on 09:26, 30 November 15
                           2) The Floppy drive does all the actions steps in and out turns the disk but won't read the disk.
                                I have not had time to look at what is wrong Yet.
Did you change the drive belt ?
Title: Re: Repairs to a CPC6128
Post by: Bryce on 10:30, 30 November 15
You can use this program - (Run it from B: with the 3.5in drive or or run from A: using the 3.5in drive and then hotswap the drives). With option 5 you can do an RPM test to check that it's spinning at the right speed).

Bryce.
Title: Re: Repairs to a CPC6128
Post by: Audronic on 10:50, 30 November 15


Quote from: gerald on 10:15, 30 November 15
There is  a chance that the drive section schematic in the amendment service manual (http://www.cpcwiki.eu/manuals/Amendment%20Service%20Manual.zip), in the 6128 cost down section. The same data separator is used.


Yes i found the missing links in the 646 and the Plus schematics.


I've attached a memory test that covers 512k expansion RAM.
It will test the 0x4000-0x7FFF main bank and all detected expansion 16K blocks.
If the extension RAM is dead and not detected, it will only test that single block.


Thanks for Memory tester

Did you change the drive belt ?

Yes the belt has been changed the disk spins. But no Read.




Thanks     Ray
Title: Re: Repairs to a CPC6128
Post by: Audronic on 10:55, 30 November 15

HI Bryce


I am unable to see the link ?


Thanks   Ray

Quote from: Bryce on 10:30, 30 November 15
You can use this program - (Run it from B: with the 3.5in drive or or run from A: using the 3.5in drive and then hotswap the drives). With option 5 you can do an RPM test to check that it's spinning at the right speed).

Bryce.
Title: Re: Repairs to a CPC6128
Post by: Audronic on 11:13, 30 November 15
Hmmmnnnn.


Unwell
How do I interpret the Photo Please


Ray
Title: Re: Repairs to a CPC6128
Post by: gerald on 11:38, 30 November 15
Quote from: Audronic on 11:13, 30 November 15
Hmmmnnnn.


Unwell
How do I interpret the Photo Please


Ray
Simple answer is : change the 2nd bank RAM  ;)

Long answer is :
The test failed to detect the 2nd bank properly. The detection is done by writing a signature byte in each of the possible bank and read it back.
The signature is written from the highest possible bank in 512k down to the 1st block of the 1st bank.
The "84 87 84 87 84 87 84 87 84 ....." is the signature readback.
Expected value for a 128k is  "80 81 82 83 80 81 82 83 ...."
A 512k expanded signature is "80 81 82 83 84 85 86 87 ..... 9C 9D 9E 9F"

Unfortunately, this test is only reporting error at byte level and cannot tell which device is OK and which is not.
Title: Re: Repairs to a CPC6128
Post by: Bryce on 12:47, 30 November 15
Quote from: Audronic on 10:55, 30 November 15
HI Bryce

I am unable to see the link ?

Thanks   Ray

Oops, link disappeared: DskTest v0.1.47b (release?) (http://www.cpcwiki.eu/forum/applications/dsktest-v0-1b/)

Bryce.
Title: Re: Repairs to a CPC6128
Post by: Audronic on 23:55, 30 November 15
@gerald (http://www.cpcwiki.eu/forum/index.php?action=profile;u=250)


"" Simple answer is : change the 2nd bank RAM ;) ""
Damn I thought that the program would be able to repair faulty RAM  :laugh:
Ok Thanks for the explanation.
Out with the SideCutters and away I go.


Ray

Title: Re: Repairs to a CPC6128
Post by: Audronic on 23:57, 30 November 15
@Bryce (http://www.cpcwiki.eu/forum/index.php?action=profile;u=225)


Thanks for the Link.
Yes it works if i put on my 3D Glasses.  >:(


Ray
Title: Re: Repairs to a CPC6128
Post by: pacomix on 19:33, 21 August 17
Hi! I would like to know what happened afterwards. Did you finish fixing this computer?


Enviado desde mi iPhone utilizando Tapatalk
Title: Re: Repairs to a CPC6128
Post by: Audronic on 00:50, 22 August 17
@pacomix (http://www.cpcwiki.eu/forum/index.php?action=profile;u=855)


Thanks for the reminder.
Yes the 2nd Bank of ram was changed and it works well now.


I must remember to say Project Finished .


Thanks


Ray
Title: Re: Repairs to a CPC6128
Post by: llopis on 15:00, 24 June 18

Sorry for the thread necromancy, but I'm very curious how you generated your RAM signal tables.When you say Pulse for Din and Pulse for Dout, are you driving those signals somehow? If so, how? When I use a logic probe all I can tell is low, high, or changes between the two.


I've been wondering about isolating some of the chips and try to check their logic behavior, but I haven't figured out how yet (short of removing them from the PCB and setting up a test rig on a breadboard).
Title: Re: Repairs to a CPC6128
Post by: Audronic on 00:14, 25 June 18
Quote from: llopis on 15:00, 24 June 18

I'm very curious how you generated your RAM signal tables.


The signals are generated by the Computer after power up


When you say Pulse for Din and Pulse for Dout, are you driving those signals somehow? 


###  No I just read them after turning on the computer


If so, how? When I use a logic probe all I can tell is low, high, or changes between the two.


###  I just used an OLD logic probe with 3 lights  LO,   HI,  and Pulsing (activity)


###  Thats all i used Nothing special.


Good Luck
Ray

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