Bad evenings repairs

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bagpuss22
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Bad evenings repairs

Postby bagpuss22 » Sat Oct 07, 2017 2:44 am

I had good intentions tonight.

I had a CST Thor with an iffy QL motherboard, so I bought a new motherboard from Rich. It sat there for a few months but
today I decided to take action.

I took off the unwanted power regulators from the new board and put them on the old board. Put the new board in the CST Thor
and all I get now is a black screen! SO I decided to check the old board. Powered it up to find garbage on the screen but also
4 of the RAM ICs were getting very hot. so I remove them and replaced them with new ones and sockets. Still noting on the screen
but the RAM was no longer getting hot.

So I decided to put in my Minerva ROM to see if this could shed any light. Next thing I know this is VERY HOT within seconds!

SO now I have a CST Thor with a black screen, an issue 5 board with garbage or blank screen and a Minerva/ToolkitII ROM that
no longer works.....

I could cry lol


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chriskgnr
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Re: Bad evenings repairs

Postby chriskgnr » Sat Oct 07, 2017 10:03 am

Maybe there is a problem with the Thor psu and the output voltages it produces.


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bagpuss22
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Re: Bad evenings repairs

Postby bagpuss22 » Sat Oct 07, 2017 5:56 pm

OK just found that the board that cooked my Minerva ROM somehow has a short around the 7805!

I removed the 7805 and carrier and I still have 0 ohm between the in and out!?

Anyone want to look at a Issue 5 circuit diagram and tell me what could cause this as I have been under a
magnifying lamp to see if there are any shorts on the board. Cannot see anything. Is this a mod for the Thor?

Russ


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bagpuss22
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Re: Bad evenings repairs

Postby bagpuss22 » Sat Oct 07, 2017 6:24 pm

Swapped the boards back.

Put the regulators back on the board from Rich and cleaned up both boards.

Rich's replacement board is now OK and running from the Sinclair PSU.

Put the original Thor board back in and I get a black screen. Sooooooo
back to diagnosing the issue with the Thor QL mainboard. Still need to find out how the 7805 In and Out are
shorted as I may need to put a new board in here at some point or power this from a Sinclair PSU.

I can only assume that the 9v+ from the Sinclair PSU fried my Minerva ROM....

Russ


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Derek_Stewart
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Re: Bad evenings repairs

Postby Derek_Stewart » Sat Oct 07, 2017 8:58 pm

Hi Russ,

I am not sure that Minerva will work the the Thor, only Argos, with special patched version for Qubide.

If you want return any of the Thor expansion boards, I could have look at them.


Regards,

Derek
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bagpuss22
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Re: Bad evenings repairs

Postby bagpuss22 » Sat Oct 07, 2017 11:21 pm

Hi Derek,

I have not got to the Thor cards yet. Still trying to get a stable system to test them with.

I was trying to use the Minerva to test the QL mainboard removed from the Thor. Looks like the 5v line
was up at whatever a normal QL PSU outputs at DC, 9volt plus! Not sure what will cope with that.

Once I get a stable system I will look at them, unless you want to try too. I seem to be hitting to many probems
just getting mine running.....

Russ


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bagpuss22
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Re: Bad evenings repairs

Postby bagpuss22 » Sun Oct 08, 2017 9:04 pm

OK!

Just a cautionary tale. If using a QL motherboard from a Thor or unknown origin, check for this>

Image

ON my Thor board the regulators are removed and this link shorts the 7805 input to output. So if you want
to use this board in a QL and then add the regulators and do not remove this, your board gets the full 9V
plus of the PSU...... :shock:


RWAP
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Re: Bad evenings repairs

Postby RWAP » Mon Oct 09, 2017 10:33 am

It would be worth putting together a quick description of what appears in the CST thor and what changes are needed to use a QL motherboard in it :)


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Derek_Stewart
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Re: Bad evenings repairs

Postby Derek_Stewart » Mon Oct 09, 2017 11:18 am

bagpuss22 wrote:ON my Thor board the regulators are removed and this link shorts the 7805 input to output. So if you want
to use this board in a QL and then add the regulators and do not remove this, your board gets the full 9V
plus of the PSU...... :shock:


Hi Russ,

I think you have wrong.

If you put the QL board onto a QL Power Supply with the 5v regulator shorted out, unregulated 9v will be applied to the 5v QL Vcc Bus. Some or all of the chips on the board will stop working.

If remember correctly, the Thor 1 expansion board has a power supply connector and the QL board needs a modification to work with the Thor 1 Power Supply. This should be stated in the Thor 1 schematics, which are all available now.


Regards,

Derek
Martin_Head
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Re: Bad evenings repairs

Postby Martin_Head » Mon Oct 09, 2017 11:31 am

Something you might have to look out for...

I seem to remember from an earlier post about the 12 volts from the Thor PSU being fed via a resistor to supply 9 volts for the Microdrives.

If the Thor has the 9 volt and 5 volt rails linked on the QL board. The 9 volt rail must be cut somewhere near the Microdrives. Otherwise the 12v via the resistor will end up going to the 5v rail via the link. Which could be bad news.



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