OK, so I found some of my dual ROM images used in 27C4096 ROMs with my Mega ST and they are byteswapped, however I's still suggest you go down the road of testing using an EPROM first, even if you have to go and find your eraser, because at the last price I paid, £7, for OTP ROMs, it's worthwhile spending the time to test first.JezC wrote: Sat Apr 19, 2025 1:01 pm Not a bad idea @PhilC...I can see if I can get the ROM out of my working H4 or the booting H5C boards and read that.
@rubber_jonnie I have some 27C4096 EPROMs but I'd have to dig out my eraser... which is hopefully somewhere in my study....![]()
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JezC H5 C5B Build - one STep beyond...?
- rubber_jonnie
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Re: JezC H5 C5B Build - one STep beyond...?
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...
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...
Re: JezC H5 C5B Build - one STep beyond...?
Yes, I will try it with an old UV EPROM 27C4096 first (that's what I have in my existing H4/H5 boards anyway, it's just that they don't have 2.06 as the other image(.
I found some images you sent me a while back and that has the 1.04 with IDE support included plus 2.06 in both non-swapped and byte-swapped formats...
I'll have a look for the eraser when I finish the other tasks later today.
Thanks again @rubber_jonnie
I found some images you sent me a while back and that has the 1.04 with IDE support included plus 2.06 in both non-swapped and byte-swapped formats...
I'll have a look for the eraser when I finish the other tasks later today.
Thanks again @rubber_jonnie
- rubber_jonnie
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Re: JezC H5 C5B Build - one STep beyond...?
No problem and good luckJezC wrote: Sat Apr 19, 2025 1:58 pm Yes, I will try it with an old UV EPROM 27C4096 first (that's what I have in my existing H4/H5 boards anyway, it's just that they don't have 2.06 as the other image(.
I found some images you sent me a while back and that has the 1.04 with IDE support included plus 2.06 in both non-swapped and byte-swapped formats...
I'll have a look for the eraser when I finish the other tasks later today.
Thanks again @rubber_jonnie

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...
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...
Re: JezC H5 C5B Build - one STep beyond...?
Ok, so found a few minutes to make the next step or three...
VGA connector soldered in, along with the xtal and xtal osc...
I was about to try and bodge the reset switch into the board but then I noticed that the one that came with my H5CB actually had two rows of pins in the centre...so I will have to dig out a switch from the parts for the H4 or H5B boards and see if that will fit any better...
Is that an unexpected issue @exxos? Or do all the reset switches now have two rows of 3 pin contacts in the centre of the switch?
Anyway, I'm out of time for now, so maybe a bit more progress at the weekend....

VGA connector soldered in, along with the xtal and xtal osc...
I was about to try and bodge the reset switch into the board but then I noticed that the one that came with my H5CB actually had two rows of pins in the centre...so I will have to dig out a switch from the parts for the H4 or H5B boards and see if that will fit any better...





Is that an unexpected issue @exxos? Or do all the reset switches now have two rows of 3 pin contacts in the centre of the switch?
Anyway, I'm out of time for now, so maybe a bit more progress at the weekend....

Re: JezC H5 C5B Build - one STep beyond...?
JezC wrote: Thu May 08, 2025 9:46 pm Or do all the reset switches now have two rows of 3 pin contacts in the centre of the switch?

No idea how that happened. I buy them in lots of 100 from mouser..

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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
Just because a lot of people agree on something, doesn't make it a fact. ~exxos ~
People should find solutions to problems, not find problems with solutions.
https://www.exxosforum.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
Just because a lot of people agree on something, doesn't make it a fact. ~exxos ~
People should find solutions to problems, not find problems with solutions.
- olivier.jan
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Re: JezC H5 C5B Build - one STep beyond...?
Mine had two rows of pins too. I initially used an old ST reset switch but it was old and flimsy. I finally ended up using the two rows ones, and it fits ok. Just bend all the pins from one of the rows so they are flat agains the bottom of the switch and resting against their counterpart on the other row.
Now gently bend the pins from the remaining ow at a 45 degrees angle and solder it to the board while pushing firmly on the switch. Et voilà...
Worked fine on my 2 H5C1, if you had the bent enclosure soldered to GND, the switch is firmly seated and looks like a normal one.
Now gently bend the pins from the remaining ow at a 45 degrees angle and solder it to the board while pushing firmly on the switch. Et voilà...
Worked fine on my 2 H5C1, if you had the bent enclosure soldered to GND, the switch is firmly seated and looks like a normal one.
Retro stuff
520 STF/ 1040 STE / Mega ST / 2 Mega STE / 2 H5
2 x 600XL with U1MB /SOFIA 2/ AVG CART / and a few 1050
Apple //c, Commodore 128, Mac Classic, SE/30, LC, IIvi and PB G3 (Clamshell)
Amiga 600 and a few 486 and 386.
Many Nintendo G&W and other electronic games from the late 70s/early 80s.
520 STF/ 1040 STE / Mega ST / 2 Mega STE / 2 H5
2 x 600XL with U1MB /SOFIA 2/ AVG CART / and a few 1050
Apple //c, Commodore 128, Mac Classic, SE/30, LC, IIvi and PB G3 (Clamshell)
Amiga 600 and a few 486 and 386.
Many Nintendo G&W and other electronic games from the late 70s/early 80s.
Re: JezC H5 C5B Build - one STep beyond...?
ah damn, nobody said the switches were wrong
It looks like I ordered them originally from RS, but was discontinued, so I ordered from mouser, and the wrong ones somehow.. totally different part number
The ones in stock are wrong as well
I've ordered the proper switches. I will have to cut a slot in the motherboard boxes and push the new switches in when the come. I don't fancy undoing and redoing up all the motherboard boxes again.
@olivier.jan Good you managed to make them fit regardless!
Others will have to do the same thing also.



I've ordered the proper switches. I will have to cut a slot in the motherboard boxes and push the new switches in when the come. I don't fancy undoing and redoing up all the motherboard boxes again.
@olivier.jan Good you managed to make them fit regardless!

https://www.exxosforum.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxosforum.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
Just because a lot of people agree on something, doesn't make it a fact. ~exxos ~
People should find solutions to problems, not find problems with solutions.
https://www.exxosforum.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
Just because a lot of people agree on something, doesn't make it a fact. ~exxos ~
People should find solutions to problems, not find problems with solutions.