Live ROM board exit and dead QL result

Nagging hardware related question? Post here!
KINGCHEF
ROM Dongle
Posts: 29
Joined: Tue Jul 20, 2021 9:52 pm

Live ROM board exit and dead QL result

Post by KINGCHEF »

Hi,
I made a mistake.
The ROM port on my QL was having trouble seeing the TK2 rom I had plugged in. I tried another board and it was O.K.
I then started swapping various boards and promptly forgot to turn it off once.
That's it dead. No screen image at all, just black.
It says in the manual not to remove the ROM when the QL is live but not what to expect if you do.


What have I damaged?

Any help much appreciated.

Dave


User avatar
Chr$
QL Wafer Drive
Posts: 1304
Joined: Mon May 27, 2019 10:03 am
Location: Sachsen, Germany
Contact:

Re: Live ROM board exit and dead QL result

Post by Chr$ »

Black screen is usually a sign that the ZX8301 has died (- in my experience and usually in relation to pulling the RGB cable out when it's on). That's the first thing I'd attempt to swap. If that doesn't work, no doubt the real experts will have suggestions!


https://QXL.WIN
Collector of QL related computers, accessories and QL games/software.
Ask me about felt pads - I can cut them to size and they have proved excellent for mdv data recovery.
User avatar
mk79
QL Wafer Drive
Posts: 1349
Joined: Sun Feb 02, 2014 10:54 am
Location: Esslingen/Germany
Contact:

Re: Live ROM board exit and dead QL result

Post by mk79 »

Yes, definitely ZX8301, it's not just vulnerable regarding the RGB lines, it's all lines, including the data and address lines that are on the ROM port. Killed one or two while developing QL-SD. If you're quick enough removing the power it can survive (<10s or so) before it suffers a fatal heat death.


User avatar
tofro
Font of All Knowledge
Posts: 2685
Joined: Sun Feb 13, 2011 10:53 pm
Location: SW Germany

Re: Live ROM board exit and dead QL result

Post by tofro »

mk79 wrote:Yes, definitely ZX8301, it's not just vulnerable regarding the RGB lines, it's all lines, including the data and address lines that are on the ROM port. Killed one or two while developing QL-SD. If you're quick enough removing the power it can survive (<10s or so) before it suffers a fatal heat death.
Yep, in my experience, it's also the first chip to die when something on the expansion port goes wrong - like a bent pin, for example (I even had it go glowingly hot - but survive with the checks below - when I had a Gold Card with a bad solder joint).

I've made it into a habit to put a finger on the 8301 and check for excessive heat when switching on for the first time after I have changed anything in the QL setup and the case open.


ʎɐqǝ ɯoɹɟ ǝq oʇ ƃuᴉoƃ ʇou sᴉ pɹɐoqʎǝʞ ʇxǝu ʎɯ 'ɹɐǝp ɥO
KINGCHEF
ROM Dongle
Posts: 29
Joined: Tue Jul 20, 2021 9:52 pm

Re: Live ROM board exit and dead QL result

Post by KINGCHEF »

Brane2 wrote:
Chr$ wrote:Black screen is usually a sign that the ZX8301 has died (- in my experience and usually in relation to pulling the RGB cable out when it's on). That's the first thing I'd attempt to swap. If that doesn't work, no doubt the real experts will have suggestions!
While at it, you might want to solder some protection diodes or simply 4.7V zeners on ULA signals ( RGB, H/V/SYNC etc) on both ULAs. ULA2 has couple of signals that go to microdrive port etc.
Hi,

Is there a circuit diagram anywhere to help me?I'm pretty good at soldering but need a design to work to.
Thanks


User avatar
Chr$
QL Wafer Drive
Posts: 1304
Joined: Mon May 27, 2019 10:03 am
Location: Sachsen, Germany
Contact:

Re: Live ROM board exit and dead QL result

Post by Chr$ »

I personally only bother adding diodes to the ZX8301 when it's a German QL (or US one, but not seen one of those yet) as on those Samsung models it was a factory fitted mod. Others, inc all the UK ones, never had them. And I've destroyed ZX8301's with or without diodes, so I don't think it's a magic cure to make them indestructible.

Here's a pic of a German chipset showing the 1N4148 diode arrangement on the ZX8301.
20201009_181043_resizegd.jpg


https://QXL.WIN
Collector of QL related computers, accessories and QL games/software.
Ask me about felt pads - I can cut them to size and they have proved excellent for mdv data recovery.
User avatar
Peter
QL Wafer Drive
Posts: 1953
Joined: Sat Jan 22, 2011 8:47 am

Re: Live ROM board exit and dead QL result

Post by Peter »

Brane2 wrote:While at it, you might want to solder some protection diodes or simply 4.7V zeners on ULA signals ( RGB, H/V/SYNC etc) on both ULAs.
Those zener diodes would be wasted work. Too slow and not limiting voltage sharply enough.


1984
ROM Dongle
Posts: 17
Joined: Sat Dec 12, 2020 5:00 pm

Re: Live ROM board exit and dead QL result

Post by 1984 »

KINGCHEF wrote:Is there a circuit diagram anywhere to help me?I'm pretty good at soldering but need a design to work to.
If no one has answered your question and if you have not found a source already: There are all kinds of circuit diagrams on Dilwyn Jones' website in the QL hardware documentation section [1]. Best to start with are the circuit diagrams of QL board issue 5 [2] and issue 6 [3] (see notes in [4]).

You probably do not have to use the circuit diagrams and your solder iron, the (most presumably defective) ZX8301 is socketed, and it is worth giving a try to replace it with a new one.

Good luck! – George


[1] http://www.dilwyn.me.uk/docs/hardware/
[2] http://www.dilwyn.me.uk/docs/hardware/QLissue5.pdf
[3] http://www.dilwyn.me.uk/docs/hardware/QLissue6.pdf
[4] http://www.dilwyn.me.uk/docs/hardware/QLschem.txt


Derek_Stewart
Font of All Knowledge
Posts: 3928
Joined: Mon Dec 20, 2010 11:40 am
Location: Sunny Runcorn, Cheshire, UK

Re: Live ROM board exit and dead QL result

Post by Derek_Stewart »

Hi,

I have never had a QL with this type of modification fitted.

The mod. was the rexistors on the 8302...


Regards,

Derek
KINGCHEF
ROM Dongle
Posts: 29
Joined: Tue Jul 20, 2021 9:52 pm

Re: Live ROM board exit and dead QL result

Post by KINGCHEF »

Hi,

Update.
Swapped the 8301 for another known working and the display is no longer black. It runs through the multi coloured memory check and then goes blank white.
It doesn't do this every time. About half the time the QL starts normally. If I turn it off it might restart O.K. or not. I did think the 7805 regulator was loose but it doesn't seem to be and I've removed it and tinned the legs just in case. I did think the power socket was dodgy but I've turned the QL off and then on without touching the computer and it's still 50/50.

5 mins later
Just went to check and now cannot get the fault to re-appear so I guess I should be happy. At least I didn't need to spend £20 replacing the 8301. I didn't break it after all.
Incidentally, I have 3 QLs and not one has 8301 marked on the chip. Also the chips I have match exactly those in my OPDs so I don't expect I'll run out, got a few of those.

Any conclusions about the mystery fault would be appreciated.


Post Reply