Author Topic: I think my 6128's expansion port is bad :(  (Read 8118 times)

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Offline blackdalek

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I think my 6128's expansion port is bad :(
« on: 05:57, 05 November 17 »
I think my CPC 6128's expansion port might be damaged.

I'd like to get Duke's M4 wifi board working correctly, but I fear this may be impossible.
The symptoms I am getting is the CPC system is highly unstable, crashing spectacularly within minutes (sometimes seconds) of having the CPC powered on with the M4 board connected. The system failure is different each time: scrolling garbage, system reset, keyboard input failure, clicking cassette reed switch, all manner of error messages... it's totally random each time.

I've tried to clean up the edge connector contacts as best as I can, but it's not helped at all. I don't have the equipment or budget to repair/replace PCB traces  :(

The only other device I have which I can test the expansion port with is a Multiface Two. The MF2is also glitchy when connected, but more stable than when the M4 board is connected. i.e. - with the multiface connected, the CPC won't crash or reset, and I can load and run programs from disk. The problems only start after I press the MF2's stop button, but even then the glitches are minor like some garbage pixels appearing on the screen, and the system can usually recover and keep on going, but not always.

Other than cleaning up the edge connector traces, what else can I try?
CPC6128 modded with ABBA switch. External 5.25" floppy drive with side switch and Multiface 2. Now also sporting a joystick splitter and M4 WiFi board.

Offline Audronic

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Re: I think my 6128's expansion port is bad :(
« Reply #1 on: 08:00, 05 November 17 »
@blackdalek


I use an eraser (Rubber) as per Photo.
Please clean both the Upper and Lower contacts.


The Eraser (Rubber) is Cut down to clean the Underside contacts.


Good Luck


Ray
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Offline rpalmer

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Re: I think my 6128's expansion port is bad :(
« Reply #2 on: 08:07, 05 November 17 »
audronics advice is one in which many expansions need to address as these (expansion connectors) can become "dirty" or even worse corroded. The later is something in which it will eventually fail completely over time.

rpalmer

Offline blackdalek

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Re: I think my 6128's expansion port is bad :(
« Reply #3 on: 09:39, 05 November 17 »
I fear my expansion port connectors may fall into the "corroded" category
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Offline Audronic

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Re: I think my 6128's expansion port is bad :(
« Reply #4 on: 10:36, 05 November 17 »
Can you post some photos of the connector top and Bottom.
Thanks   Ray
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Offline khaz

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Re: I think my 6128's expansion port is bad :(
« Reply #5 on: 13:54, 05 November 17 »
I use a record cleaner solution I bought on ebay to clean contacts. Put a few drops on the tip of a cotton swab and rub that hard on each individual pin. I used an eraser before but wasn't satisfied with the result. I'm using this product specifically, got myself a 50ml bottle and most of it is still unused after cleaning a dozen of game cartridges.

If the contacts are corroded you can apply a small amount of solder over the corrosion: put a blob on it then remove it with a braid. It will leave a very thin layer of lead over the faulty contact.

And if the traces are broken you will need to use wires to repair them.

[edit]

Quote
Other than cleaning up the edge connector traces, what else can I try?

Test the continuity between the CPC board and the expansion. Use a multimeter (most have that option), follow the trace of the first pin on the cpc to the nearest component, and do the same on the expansion board. test continuity between these two components. Do that for each 50 pins.

But it's very likely you just haven't cleaned them well enough.
« Last Edit: 14:20, 05 November 17 by khaz »

Offline pelrun

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Re: I think my 6128's expansion port is bad :(
« Reply #6 on: 15:07, 05 November 17 »
I went with the nuclear option and soldered locking pin headers directly to the edge connectors. Also means I can easily make up new cables without having to hunt down more obsolete connectors.

Offline Audronic

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Re: I think my 6128's expansion port is bad :(
« Reply #7 on: 00:13, 06 November 17 »
@pelrun


Do you have some Photos Please


Ray
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Offline ||C|-|E||

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Re: I think my 6128's expansion port is bad :(
« Reply #8 on: 00:41, 06 November 17 »
When the edge connectors fail, it can be a very good time to upgrade to centronics  :) Sadly, this means that you will have to modify the case too... but it is quite worth it, in my opinion  :)

Offline pelrun

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Offline Audronic

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Procrastinators Unite,
If it Ain't Broke PLEASE Don't Fix it.
I keep telling you I am Not Pedantic.
As I Live " Down Under " I Take my Gravity Tablets and Wear my Magnetic Boots to Keep me from Falling off.

Offline blackdalek

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Re: I think my 6128's expansion port is bad :(
« Reply #11 on: 16:42, 17 November 17 »
OK. I finally got a chance to take the CPC apart again (looking after a 3 month old is time consuming lol!)
Examining it under better light, the tracks don't actually look as bad as I thought they did. Attached are some photos of the expansion port top and underside.
What do you think? They look OK to me I guess, but I'm no expert....
CPC6128 modded with ABBA switch. External 5.25" floppy drive with side switch and Multiface 2. Now also sporting a joystick splitter and M4 WiFi board.

Offline blackdalek

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Re: I think my 6128's expansion port is bad :(
« Reply #12 on: 16:48, 17 November 17 »
OK, I must be doing something wrong, because every time I try to attach a jpg I get an error...
  An Error Has Occurred!    Your attachment has failed security checks and cannot be uploaded. Please consult the forum administrator.
CPC6128 modded with ABBA switch. External 5.25" floppy drive with side switch and Multiface 2. Now also sporting a joystick splitter and M4 WiFi board.

Offline blackdalek

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Re: I think my 6128's expansion port is bad :(
« Reply #13 on: 17:23, 17 November 17 »
Going to try something... removed the exif and xmp data from the files...
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Offline khaz

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Re: I think my 6128's expansion port is bad :(
« Reply #14 on: 17:34, 17 November 17 »
Do you have a continuity tester?

Offline blackdalek

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Re: I think my 6128's expansion port is bad :(
« Reply #15 on: 14:24, 18 November 17 »
Do you have a continuity tester?

I have a multimeter with continuity test, yes. I'll try to test all the pins tomorrow.
CPC6128 modded with ABBA switch. External 5.25" floppy drive with side switch and Multiface 2. Now also sporting a joystick splitter and M4 WiFi board.

Offline gerald

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Re: I think my 6128's expansion port is bad :(
« Reply #16 on: 14:44, 18 November 17 »
Do you have a spare Z80 by chance ?
My original 464 once started to be unstable will all its extension connected and It worked fine without.
Replacing the Z80 solved the problem.

Offline blackdalek

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Re: I think my 6128's expansion port is bad :(
« Reply #17 on: 03:54, 19 November 17 »
Update:

 [ You are not allowed to view attachments ]

I've plugged the M4 board in and performed continuity test between the 50-pin connector pins on the M4 and the solder spots between the CPU and the PCB edge. All pins showed continuity with resistance between 0.7 and 0.5 ohms.
I then tested continuity between the solder spots and the CPU leg sockets... again all contacts gave 0.7 to 0.5 ohms.
Is this good or bad?
What should I test next? Is it time to test a new Z80A? I have no spares :(
CPC6128 modded with ABBA switch. External 5.25" floppy drive with side switch and Multiface 2. Now also sporting a joystick splitter and M4 WiFi board.

Offline blackdalek

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Re: I think my 6128's expansion port is bad :(
« Reply #18 on: 00:33, 21 November 17 »
Where can I get a suitable working Z80A CPU to test with? Does anyone on the forum want to sell me one? :)
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Offline Duke

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Offline blackdalek

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Re: I think my 6128's expansion port is bad :(
« Reply #20 on: 06:37, 21 November 17 »
Does it have to be a Z80A CPU or can it be any Z80 CPU?
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Offline blackdalek

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Re: I think my 6128's expansion port is bad :(
« Reply #21 on: 09:49, 10 March 18 »
An update...


After thoroughly cleaning and recoating all 50 contacts of the expansion edge connector.... I'm still experiencing flaky and unstable operation no matter what I connect to the expansion port.

So perhaps it's not my edge connectors after all?

Next I will try replacing my Z80. I have no spare to use, so I will have to order one off ebay. This could take between 10-30 days.
Does anyone in Australia have a spare Z80A they wish to sell me so I can get one faster? ;)


EDIT:

I'm starting to get pretty desperate to fix my CPC6128 expansion port problem. I'm beginning to wonder if I should just pack the main logic board into an old keyboard box and mail it to someone more technically minded and pay them to fix it for me...  :-[

Is there anyone in Australia willing to examine my 6128 motherboard if I post it to them? ;) I'd pay you for your time of course.

The symptoms are: Plugging any kind of device into the expansion port gives varying and unpredictable results, and depending on the device, can make the whole CPC so unstable it crashes after a few seconds of putting the CPU under load. Anything can happen when powering on the CPC with a device connected to the expansion ranging from a few pixels of garbage, to a jumbled screen to no sign on message at all and no monitor picture. Another quirk that occurs from time to time is the keyboard gets scrambled so that the key you press does not correspond to what appears on the screen. Other times the tape relay switch might click or the disc drive may suddenly spin up.

I've tested and re-tested the continuity of the traces to the edge connector finger plates and the resistance and conductivity always seems good.

In desperation, (lacking any kind of proper electro plating kit) I went ahead and painted over every one of the 50 finger with spot of solder in the hopes that this might fix it. Continuity test results never changed - every pin on the expansion port still seemed to be working great.... but the unstable CPC problem persisted.

I've pulled the Z80 CPU and cleaned its socket out with a blast of compressed air. Reseated in and still the problem persists. I don't yet have any other CPU to test with.

I've run out of ideas of what else to try. I don't know what else I should test next. :(
« Last Edit: 16:01, 10 March 18 by blackdalek »
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Offline Audronic

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Re: I think my 6128's expansion port is bad :(
« Reply #22 on: 12:03, 11 March 18 »
Z80 Posted


Ray
Procrastinators Unite,
If it Ain't Broke PLEASE Don't Fix it.
I keep telling you I am Not Pedantic.
As I Live " Down Under " I Take my Gravity Tablets and Wear my Magnetic Boots to Keep me from Falling off.

Offline blackdalek

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Re: I think my 6128's expansion port is bad :(
« Reply #23 on: 12:08, 11 March 18 »
Thanks Ray.
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Offline blackdalek

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Re: I think my 6128's expansion port is bad :(
« Reply #24 on: 03:08, 16 March 18 »
The replacement Z80 did not make any difference :(
I am still experiencing random glitches and crashes while anything is plugged into my expansion port.
Other than the contacts of the edge connector, what else can I check?

Is there some other component between the edge connector and the Z80 I should check which may be causing the problem?

I realise now that my CPC has probably had this issue since I bought it.
I bought a PACE RS232 interface many years ago which never worked and always crashed. I always assumed the RS232 was broken and resold it as not working. The only other device I have ever had connected is a Multiface 2, and although it worked most of the time, it occasionally froze or put garbage up on the screen when I pressed the red button. I just assumed that was normal for the device. Looking back now, the RS232 was probably perfectly fine and I gave it away for next to nothing thinking it was broken :(

Fast forward to 2018.... I've recently started collecting new gadgets to connect, and only now I've started to realise my CPC was at fault and not the devices I connected.
« Last Edit: 03:22, 16 March 18 by blackdalek »
CPC6128 modded with ABBA switch. External 5.25" floppy drive with side switch and Multiface 2. Now also sporting a joystick splitter and M4 WiFi board.