cpc464 not booting, but was before.

Novabug · 14:18, 05 October 14

Hey guys, bit of issue which I'm gutted about.

Was using my fully working 464, when suddenly it reset during a game and crashed. I switched off and back on, only to be greeted with a screen full of graphic jumble. https://www.facebook.com/photo.php?fbid=10152418150025028&set=gm.10152415212837058&type=1&theater

Sometimes, it displays the first lines of the start screen, without the BASIC prompt, and doesn't respond at all.

It has been suggested this maybe a number of things.... The gate array, the RAM chips or even the Z80. I have re-seated the gate array with no effect. Checked the power switch and checked the monitor with my other cpc. That works fine. What could this be?

The pcb is clean, chips are not warming up and the caps are not swollen. I can swap the Z80 to test, but it that don't work I'm stumped.

Bryce · 14:24, 05 October 14

Hi Novabug,
I'd say a RAM has failed.

Bryce.

Novabug · 14:50, 05 October 14

Quote from: Bryce on 14:24, 05 October 14
Hi Novabug,
I'd say a RAM has failed.

Bryce.

That was my first thought too, but I can't seem to identify which one or more are heating up. they all seem pretty cool after about 5 minutes switched on. Don't like to leave it on for long in this state however.

Bryce · 15:55, 05 October 14

Broken RAMs don't always get hotter.

Bryce.

Novabug · 16:02, 05 October 14

Quote from: Bryce on 15:55, 05 October 14
Broken RAMs don't always get hotter.

Bryce.

so I have no way of knowing which one? agrh, these 2 cpc's are doing my nut in. lol

Novabug · 21:25, 05 October 14

I have access to 15 4264-15 RAM chips out of a 6128. Are they suitable replacments for the 4164-15's that are in it already?

Novabug · 20:03, 16 October 14

This is what I'm getting.... any advice good people?

VID 20141005 103841 - YouTube

Devilmarkus · 20:29, 16 October 14

When you remove the BASIC ROM in an emulator, the same problem happens...
So, perhaps the ROM is corrupt?

Bryce · 21:19, 16 October 14

Na, that's too random. I'd clean the power switch contacts first. That looks like a "Brown-out" or power problem. Disconnect the power switch wire from the PCB, bridge the contacts with a jumper and see if it boots then.

Bryce.

Novabug · 23:36, 16 October 14

Bypass the power switch essentially then? I'll try that.

Bryce · 08:14, 17 October 14

Quote from: Novabug on 23:36, 16 October 14
Bypass the power switch essentially then? I'll try that.

Exactly.

Bryce.

Novabug · 09:43, 17 October 14

Done. No effect. Still randomly display graphic mess, sometimes with a flashing ready screen.

Bryce · 09:56, 17 October 14

Hmm, ok. What measurement equipment do you have? Can you measure what voltage is on the 5V rail?

Bryce.

Novabug · 10:01, 17 October 14

I have a pretty decent multimetre which I can adjust to low voltage DC. Another thing, the solders on the input jack look a little dry. This could be a factor? I also have tried 3 differing power supplies (2 monitors and a av adapter) with the same result.

Bryce · 15:06, 17 October 14

Yes, dry joints will cause problems of course, give them a re-flow.

Bryce.

Novabug · 21:12, 20 October 14

Completely re-seated the input jack. Brand new solder. Still the same result. I did a long session of switching on and off and sometimes, the start screen appears stable, but without Ready prompt or curser. Beginning to think this might be the ROM after all.

Bryce · 21:27, 20 October 14

It might be, but the randomness of it points at a power problem. How's the main electrolytic capacitor looking?

Bryce.

Novabug · 21:34, 20 October 14

Large blue one by the MB connector? Looks sound, not puffed and solders are clean. Trying to find a ROM chip at the moment. AmsDOS 40015. Is that right?

Bryce · 21:54, 20 October 14

AmsDOS is the floppy firmware. It's more likely that the Firmware/Basic ROM is dodgy. You don't need to source an original, you can burn the image to any 32K EPROM.

Bryce.

Novabug · 22:06, 20 October 14

I don't have the facilities to do that mate. I would much rather replace the chip if possible. I guess a 40009 would be a straight replacement?

CraigsBar · 23:45, 20 October 14

Quote from: Novabug on 22:06, 20 October 14
I don't have the facilities to do that mate. I would much rather replace the chip if possible. I guess a 40009 would be a straight replacement?

I can burn one for you if you need one, I have a Eprom Programmer and some spare eproms... I might even have a spare around here. One of my 6128plus machines has a Dual Bios in it that boots to Mode 2 and a different font. I plan on reprogramming this to make the alternate OS FW3.15 at some point

Not got around to that yet tho

Craig

Novabug · 22:11, 21 October 14

I appreciate the offer mate, may take you up on that it's I find I'm getting nowhere with a replacement.

Looking on picking up to salvaged 464's at the moment, to see if I can somehow cobble together a working one. ha

CraigsBar · 23:00, 21 October 14

No worries, these are my originals.

2x ams40025 (6128 fw&basic)
3x ams40015 (amsdos)

And I can of course flash burn anything you need.

Craig

CraigsBar · 23:01, 21 October 14

Novabug · 20:27, 07 November 14

So, after messing around with the firmware chip. Nothing worked. So I just replaced the entire pcb with a loose one I found on Ebay. Works a treat. Will be taking the AY and 74LS off to put in my other CPC, the rest of the board is up for grabs. Free of course, just postage.

Not sure what the actual problem is, but the CPU works at least. I may be a faultly ROM or Ram chip. Thanks for the help and guidance though guys.

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cpc464 not booting, but was before.