Brett's STE - Repair thread

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rubber_jonnie
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Re: Brett's STE - Repair thread

Post by rubber_jonnie »

exxos wrote: Sun Jan 23, 2022 12:20 am
rubber_jonnie wrote: Sun Jan 23, 2022 12:14 am They look original, and funnily enough I haven't changed them in my own STE. But I can change them whilst I'm at it, but reluctant to change too much else until I am 100% sure I have all the wiring right.
I half recall bodge wires to resistor packs at one point ? I know you metered a lot out. But checking the pins actually have pull ups will check a lot of traces etc as well. The actual resistance *shouldn't* matter at this point..

Also not sure if you're pressing reset button during tests ? Would be typical to actually have fixed it and the reset circuit died...
There aren't any bodge wires to resistor packs, and I don't think there were originally, but I'll check there are pull ups on all the data lines.

I have one data line that is behaving differently to my working machine, in that it is low until I hit reset, so provided my wiring is good, which I will check again, and check out to the RPs.

I'll see what that data line is doing elsewhere as far as I can.
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Re: Brett's STE - Repair thread

Post by rubber_jonnie »

Ok, so that data line is now fixed, I'd missed a wire out, and I am about 90-95% confident the trace damage is correctly fixed. Still no boot yet though.

I also came back to the concern that there was a short. My own STE draws about 1.2 amps during boot and on reaching the desktop, but Brett's is pulling nearly about 1.5, and I noticed because I had set over current protection at 1.5A on my bench PSU and it was showing the limit was just about hitting.

I decided to start pulling components, to see what was drawing the extra current, and it turned out to be the CPU. An extra 300ma drawn by the CPU, OK, so does the CPU actually work?

So I tested it in my own STE, and it does work just fine. The difference is that my own STE has an HC variant which runs around 300ma less than the standard 68000.

Anyway, I got into testing all of the chips I could, and the CPU and Shifter all work in my machine, so that's a good start. I already knew the ROMs worked in my machine.

Also of note is that with the CPU removed, the boot screen is the same as with it fitted.

I did quickly check the clocks and the CPU has 8Mhz just fine, though I need to check the clocks elsewhere, so have to go and find the pinouts for the PLCC shifter and the MMU/GLUE combo chip. The Blitter is a separate item here.

Of note is that the CPU /HALT line is low, therefore active, I suspect as a result of the CPU either getting bad or no data at boot time. /RESET seems to work, transitioning to low when reset is pressed, then back to high. Perhaps it's time to bring out my 16CH logic analyser and see what the address lines do at boot, as if they are screwed up, we won't be getting any data out of the ROMs, or we'll get data from the wrong location.

Then more scoping etc and comparison to my working machine required.
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Re: Brett's STE - Repair thread

Post by exxos »

Yikes. So have you tested BERR pin ? I assume that goes low then HALT does ? That would mean the CPU is trying to access something and it's not responding.

After reset, do you at least see ROM CE pulse low ? ( assuming dualtos board fitted ) you should get several pulses low when the CPU is accessing ROM, if not, then something is wrong on the address bus. Maybe a break from the CPU to the GST ?

It's one of those annoying things again, where you really need to hardwire the whole address bus to 0v along with /AS /UDS /LDS as then the GST should see address zero, then ROM CE will go low and put the ROM start address on the bus.
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Re: Brett's STE - Repair thread

Post by sporniket »

rubber_jonnie wrote: Sun Jan 23, 2022 11:39 pm I did quickly check the clocks and the CPU has 8Mhz just fine, though I need to check the clocks elsewhere, so have to go and find the pinouts for the PLCC shifter and the MMU/GLUE combo chip. The Blitter is a separate item here.
The Kicad symbol used in my schematic is generated from a human friendly markdown formatted datasheet here : https://github.com/sporniket/kicad-symb ... shifter.md

And there is a link inside to the info-coach page that explains the general theory of operation of said shifter.
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Re: Brett's STE - Repair thread

Post by rubber_jonnie »

exxos wrote: Mon Jan 24, 2022 12:14 am Yikes. So have you tested BERR pin ? I assume that goes low then HALT does ? That would mean the CPU is trying to access something and it's not responding.
Not yet, I ran out of time yesterday evening to go much further than above. I will check at the next opportunity.
exxos wrote: Mon Jan 24, 2022 12:14 am After reset, do you at least see ROM CE pulse low ? ( assuming dualtos board fitted ) you should get several pulses low when the CPU is accessing ROM, if not, then something is wrong on the address bus. Maybe a break from the CPU to the GST ?
Yes, /CE is consistent with my working machine, with or without ROMs fitted. I am not using the Dual TOS atm, though it is repaired and works in my machine, but I am using the original ROMs, which work just fine too, as access for scoping is easier. I am seeing pulses on all the address lines, but they are 'messy'.
exxos wrote: Mon Jan 24, 2022 12:14 am
It's one of those annoying things again, where you really need to hardwire the whole address bus to 0v along with /AS /UDS /LDS as then the GST should see address zero, then ROM CE will go low and put the ROM start address on the bus.
Indeed, and certainly something to consider.
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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Re: Brett's STE - Repair thread

Post by rubber_jonnie »

sporniket wrote: Mon Jan 24, 2022 8:46 am
rubber_jonnie wrote: Sun Jan 23, 2022 11:39 pm I did quickly check the clocks and the CPU has 8Mhz just fine, though I need to check the clocks elsewhere, so have to go and find the pinouts for the PLCC shifter and the MMU/GLUE combo chip. The Blitter is a separate item here.
The Kicad symbol used in my schematic is generated from a human friendly markdown formatted datasheet here : https://github.com/sporniket/kicad-symb ... shifter.md

And there is a link inside to the info-coach page that explains the general theory of operation of said shifter.
Thanks, I'll look into that, appreciate the info.
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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Re: Brett's STE - Repair thread

Post by Badwolf »

rubber_jonnie wrote: Mon Jan 24, 2022 9:09 am Yes, /CE is consistent with my working machine, with or without ROMs fitted. I am not using the Dual TOS atm, though it is repaired and works in my machine, but I am using the original ROMs, which work just fine too, as access for scoping is easier. I am seeing pulses on all the address lines, but they are 'messy'.
How many pulses are you seeing? If it's more than a couple, try the ROM3/ROM4 lines on the cartridge port. If they toggle too, you might be into diag cart territory.

I'd be thinking a data bus (or possibly address) short between lines at this point.

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Re: Brett's STE - Repair thread

Post by rubber_jonnie »

Badwolf wrote: Mon Jan 24, 2022 1:41 pm
rubber_jonnie wrote: Mon Jan 24, 2022 9:09 am Yes, /CE is consistent with my working machine, with or without ROMs fitted. I am not using the Dual TOS atm, though it is repaired and works in my machine, but I am using the original ROMs, which work just fine too, as access for scoping is easier. I am seeing pulses on all the address lines, but they are 'messy'.
How many pulses are you seeing? If it's more than a couple, try the ROM3/ROM4 lines on the cartridge port. If they toggle too, you might be into diag cart territory.

I'd be thinking a data bus (or possibly address) short between lines at this point.

BW
Do you mean the /CE pulses? Yes it's more than a couple, but the diag cart doesn't work, though I haven't checked the cart lines, but will do, thanks.

I'm going to record the boot process with my LA, see how it compares to my working machine.
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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Re: Brett's STE - Repair thread

Post by Badwolf »

rubber_jonnie wrote: Mon Jan 24, 2022 1:47 pm I'm going to record the boot process with my LA, see how it compares to my working machine.
Incidentally, if you have the ability to burn ROMs, there does exist Terriblefire's ST version of 'DiagROM'

https://github.com/terriblefire/diagromst

Which requires fewer things to work before it gets a screen up.

BW
DFB1 Open source 50MHz 030 and TT-RAM accelerator for the Falcon
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Re: Brett's STE - Repair thread

Post by rubber_jonnie »

Badwolf wrote: Mon Jan 24, 2022 2:17 pm
rubber_jonnie wrote: Mon Jan 24, 2022 1:47 pm I'm going to record the boot process with my LA, see how it compares to my working machine.
Incidentally, if you have the ability to burn ROMs, there does exist Terriblefire's ST version of 'DiagROM'

https://github.com/terriblefire/diagromst

Which requires fewer things to work before it gets a screen up.

BW
I can burn ROMs, yes, so may give that a go, thanks again for your help here :)
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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