Broken 6128?

[Blurredman]

Hello chaps!


Well I got this 6128. I put it into the monitor to see if it would work. I put the volume up so I could hear if it was on. Whist on, the power light was okay for several seconds but no display would appear.

Then, the light went out and I could hear nothing. The computer seems to have gone.

If I turn off the monitor with the computer on, then turn the monitor back on, the light flashes once and I can hear a little click from the disc drive.
The same happens when the computer is turned on after the monitor has been off. Is it just static?

There did come with it a generic 5v power transformer, and when I use that the light does come on and there is a high pitch whistle. Is this side effect of the power adapter being incorrect or something else? The monitor works fine with my 464..

Or does it look like it is broken?

[arnoldemu]

Hello chaps!


Well I got this 6128. I put it into the monitor to see if it would work. I put the volume up so I could hear if it was on. Whist on, the power light was okay for several seconds but no display would appear.

Then, the light went out and I could hear nothing. The computer seems to have gone.

If I turn off the monitor with the computer on, then turn the monitor back on, the light flashes once and I can hear a little click from the disc drive.
The same happens when the computer is turned on after the monitor has been off. Is it just static?

Or does it look like it is broken?

it could be the power in the monitor itself.
disconnect the 12v cable, so cpc takes less from monitor.

or, if possible try it with an alternative monitor or power supply.

the monitors have something in them which fails with age (voltage regulator? transistor??). I remember it going on my monitor, and it would cause it to just shut off.

this would cause power problems.

another thing to check out, is the power switch on the cpc may be bad, it may need to be taken out, dismantled, and cleaned and then put back together - I have found this on one cpc, and when I cleaned it, it worked great after.

also clean the connectors for the power if you can.

another thing to also try is to clean the edge connectors just in case there is some kind of short on them.

[Blurredman]

 Oh god, I think I just ffffed up the situation very drastically.


Looking at the supply that has been provided it seems to be the culplrit. It's 18v, and it's a pitty I didn't see that before I plugged it into the 464!

Now neither of thecomputers boot using normal monitors (i have a green screen too) and the only way to get them to boot would create a blank screen box in the centre of the screen using the other power adapter.

I have ffffed it ffffing up!! ffs. It looks like I have two dead CPC's, just. like. that. 

[Bryce]

Yes, that will have certainly killed them. The whistling sound was probably the transformer overloading as the current rose (because it was burning through the ICs), I doubt either are repairable at this stage. If you are really, really lucky, then only one component shorted completely and saved the others, but it would take some major work to find out what had survived and what's dead.

Don't plug them into the monitors any more, otherwise you'll have two dead monitors too.

Bryce.

[arnoldemu]

18v into the 5v?
or 18v into the 12v?

I'm hoping you broke something that wasn't too important and which can be replaced.

blank screen box indicates crtc is probably working, z80 probably too.
not sure what could be wrong.

[Blurredman]

Well the 6128 is DOA, cost me a fair bit of money.

The 464's are common enough but it's just upsetting.

I've got two computers weighing a few lbs which ain't worth shit no more, minus expence.

[Bryce]

Well the fact that the 18V was plugged into the 5V socket isn't good (I assume it was the 5V, because, (A) A 464 doesn't have a 12V connection, and (B) I assume the PSU had a plug and not a socket). However, if you are getting a box in the middle of the screen all may not be lost and they might be repairable, but it's not going to be an easy repair.

Bryce.

[arnoldemu]

I may be able to modify my emulator to simulate this fault. it may give a better idea to what has gone wrong.

[Bryce]

The problem is, the CPC doesn't have any power protection inside the keyboard, all the protections (Over-voltage and over-current) are within the monitor, so plugging 18V into the 5V socket supplied all the ICs with way too much voltage. The smoothing capacitors and resistors can all take 18V, but most ICs will burn through at about 7V. In the best case scenario, one of the cheaper and easily replaceable 74LSxx ICs went first (and quickly) causing a full short-circuit and saved the other IC's, but if the weakest link was the AY or any other custom IC, then it's not good.

There is a repair-service guy here (Spain or Portugal I think). Or if you like, you could send me the PCBs (not the whole CPC, case, Keyboard!) and I could take a look at whether there's anything worth saving.

Bryce.

[Blurredman]

Well, there happens to be the same model motherboard on ebay. I'm going to try and go for that, hopefully others on this forum and elsewhere don't have the same ideas.

The guy selling the 6128 covered himself well.

[Bryce]

Why was there a 18V PSU included with the CPC? Are you sure it really supplies 18V?

I just took a quick look through the Datasheets: The most likely candidates (what went bang first) are the ULA, Z80, CRTC and AY, followed by the Memory shortly afterwards, the ROM would fail next and the the 74 Logic ICs last. The fact that the CRTC still seems to work, would suggest that the Z80, ULA or AY has fully shorted and possibly protected the rest.

Bryce.

[arnoldemu]

Why was there a 18V PSU included with the CPC? Are you sure it really supplies 18V?

I just took a quick look through the Datasheets: The most likely candidates (what went bang first) are the ULA, Z80, CRTC and AY, followed by the Memory shortly afterwards, the ROM would fail next and the the 74 Logic ICs last. The fact that the CRTC still seems to work, would suggest that the Z80, ULA or AY has fully shorted and possibly protected the rest.

Bryce.

I think the z80 must be working to some degree because it set up the crtc, and the gate-array too, because you are getting a display.
I think ay/memory could be bust... but I can't be sure for definite.

[Blurredman]

Why was there a 18V PSU included with the CPC?

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=320710088078&ssPageName=STRK:MEWNX:IT


That's what it was. I assume any idiot who wanted to test something at least reads the power requirements and doesn't stick any old phone charger or whatever in it.

I only used it (and consequently blew my 464) because my dad said, surely try the power adapter supplied with it to see if it is the monitor at fault. God if I could turn back time!

[AMSDOS]

I can only presume it would have costed too much money to standardise which voltage power female connector could fit which male plug, that hurts bad when things are the way they are! 

[Bryce]

@Arnoldemu: Would the default settings of the CRTC not give a box? If not, then the Z80 and ULA might be OK, and if the box is blank/all one colour, that would suggest that the memory might have survived too, otherwise you would have random colours all over the place? So my bets are on the AY.

Bryce.

[arnoldemu]

@Arnoldemu: Would the default settings of the CRTC not give a box? If not, then the Z80 and ULA might be OK, and if the box is blank/all one colour, that would suggest that the memory might have survived too, otherwise you would have random colours all over the place? So my bets are on the AY.

Bryce.

Assuming it's a standard CRTC (not a costdown; no idea what it defaults to), then defaults are all 0's for the registers with no hsync and no vsync, so you should expect a black screen if it's gone. To get a letter box z80 must have executed the rom enough to set it up. Also, crtc doesn't generate the video, the ULA does. So chances are that is working to some degree.

[Blurredman]

I would say at this point that neither machine even boot up (and therefore give a display at all) without the 18v transformer. Nothing appears at all using the proper 5v one..

[arnoldemu]

I would say at this point that neither machine even boot up (and therefore give a display at all) without the 18v transformer. Nothing appears at all using the proper 5v one..

ok, if the power light is on and the screen is black, then it could be anything at all.

[Bryce]

R.I.P.

Well you can always use them for spare parts (as the original ebay seller suggested).

Bryce.

[Blurredman]

ok, if the power light is on and the screen is black, then it could be anything at all.

No power light. Or at least, only for a split second when you touch the switch.

[Blurredman]

I've just had another try (with the greenscreen)

And, the 464 does indeed power up with a box. All one colour, as far as i can make out between the verticle lines on such a screen..

BUT, this only happens when the computer is turned on BEFORE the monitor. If the monitor is turned on before the computer then nothing.



Unfortunately, the same does not happen with the 6128, it simply makes the screen flicker once (but brightly) when turning on. Either way, i'm going to be looking for a replacement board for the 6128.

A question however, would it be safe to be switching such chips you describe between the completely broken 6128 to the 464 in a hope that grasping straws, what might not work on the 464 works on the 6128? Or the fact that nothing comes on means that everything is gone?

[arnoldemu]

I've just had another try (with the greenscreen)

And, the 464 does indeed power up with a box. All one colour, as far as i can make out between the verticle lines on such a screen..

BUT, this only happens when the computer is turned on BEFORE the monitor. If the monitor is turned on before the computer then nothing.



Unfortunately, the same does not happen with the 6128, it simply makes the screen flicker once (but brightly) when turning on. Either way, i'm going to be looking for a replacement board for the 6128.

A question however, would it be safe to be switching such chips you describe between the completely broken 6128 to the 464 in a hope that grasping straws, what might not work on the 464 works on the 6128? Or the fact that nothing comes on means that everything is gone?

most of the chips are normally soldered except the z80 and perhaps gate-array.

you can't just swap the gate-array unless they are exactly the same model.

[Bryce]

I wouldn't advise it either. The 464 may be repairable, but I think the 6128 may have been broken before it ever got to you.

Bryce.

[Blurredman]

 Very well. I won't make it worse then 


As far as the 6128 is concerned, I am trying to get a replacement mainboard.

As for the 464, the colour is constant but every few lines (2 or 3) there is a darker line. What does that suggest in terms of replacing chips?

[arnoldemu]

Can you make a photo of the problem?