Re: Resistor R55
Quoting Leszek Chmielewski retr...@gmail.com: My SAM has no BRIGHT too. There was a shortcut between Composite and +12V, so the MC1377P was burned out (Just got a replacement by desoldering a Atari Mega STE), I lost BRIGHT too as the ASIC was toasted a little too. After replacing it with ASIC from my spare SAM the BRIGHT is back again. It is time to design a replacement ASIC. Velesoft is working on one since years, but he is too ambitious: 4096 Colours, Hardware sprites and scrolling... LCD A replacement ASIC is ambitious - but these days, not impossible. Could we use the work done on the Spectrum ULA to give a start to this?
Re: Resistor R55
- Original Message - From: Leszek Chmielewski To: sam-users@nvg.ntnu.no Sent: Tuesday, October 04, 2011 11:11 AM Subject: Re: Resistor R55 My SAM has no BRIGHT too. There was a shortcut between Composite and +12V, so the MC1377P was burned out (Just got a replacement by desoldering a Atari Mega STE), I lost BRIGHT too as the ASIC was toasted a little too. After replacing it with ASIC from my spare SAM the BRIGHT is back again. It is time to design a replacement ASIC. Velesoft is working on one since years, but he is too ambitious: 4096 Colours, Hardware sprites and scrolling... LCD Hi. My project is SAM COUPE clone (but no ASIC replacement). First prototype will based on big CPLD + fast Z80cpu + big sram + saa1099 sound chip. Here is components for first SAM clone: http://velesoft.speccy.cz/other/ula-xc95288xl.jpg http://velesoft.speccy.cz/IMGP3176.JPG http://velesoft.speccy.cz/IMGP3178.JPG Priorities: - compatibility with SAM COUPE - more colours (minimal 256 colors palette) - faster CPU - possibility run at full speed 6MHz in all graphic modes (not contended memory) - better compatibility with ZX Spectrum (ZX mode can work as ZX128) - big ram + big rom - internal peripherals... Actuallly I must finish ZX projects: K-MOUSE 2011, complette RGBVGA convertor, ULA1 clone (zx clone based on old russian chil ULA1). After it I can continue on SAM projects... VELESOFT
Re: Resistor R55
Look forward to seeing more on this. What status are you at with the ASIC module? Are you looking at replacing the 1772 as well? Any plans to make the ASIC code available - as it may allow others to help with your development perhaps? Quoting VELESOFT veles...@seznam.cz: - Original Message - From: Leszek Chmielewski To: sam-users@nvg.ntnu.no Sent: Tuesday, October 04, 2011 11:11 AM Subject: Re: Resistor R55 My SAM has no BRIGHT too. There was a shortcut between Composite and +12V, so the MC1377P was burned out (Just got a replacement by desoldering a Atari Mega STE), I lost BRIGHT too as the ASIC was toasted a little too. After replacing it with ASIC from my spare SAM the BRIGHT is back again. It is time to design a replacement ASIC. Velesoft is working on one since years, but he is too ambitious: 4096 Colours, Hardware sprites and scrolling... LCD Hi. My project is SAM COUPE clone (but no ASIC replacement). First prototype will based on big CPLD + fast Z80cpu + big sram + saa1099 sound chip. Here is components for first SAM clone: http://velesoft.speccy.cz/other/ula-xc95288xl.jpg http://velesoft.speccy.cz/IMGP3176.JPG http://velesoft.speccy.cz/IMGP3178.JPG Priorities: - compatibility with SAM COUPE - more colours (minimal 256 colors palette) - faster CPU - possibility run at full speed 6MHz in all graphic modes (not contended memory) - better compatibility with ZX Spectrum (ZX mode can work as ZX128) - big ram + big rom - internal peripherals... Actuallly I must finish ZX projects: K-MOUSE 2011, complette RGBVGA convertor, ULA1 clone (zx clone based on old russian chil ULA1). After it I can continue on SAM projects... VELESOFT
Re: Resistor R55
Hopefully we understand the behaviour of the current ASIC well enough for someone to create a replacement, or (as you're suggesting) and enhanced version that is backwards compatible. It's not a small task though! I have a bunch of test programs that Dave and I wrote for SimCoupe, which tested tested various fringe cases and display quirks. It'd be cool for those to contribute back to real hardware :) Si On 8 Oct 2011, at 15:03, VELESOFT wrote: Hi. My project is SAM COUPE clone (but no ASIC replacement). First prototype will based on big CPLD + fast Z80cpu + big sram + saa1099 sound chip. Here is components for first SAM clone: http://velesoft.speccy.cz/other/ula-xc95288xl.jpg http://velesoft.speccy.cz/IMGP3176.JPG http://velesoft.speccy.cz/IMGP3178.JPG Priorities: - compatibility with SAM COUPE - more colours (minimal 256 colors palette) - faster CPU - possibility run at full speed 6MHz in all graphic modes (not contended memory) - better compatibility with ZX Spectrum (ZX mode can work as ZX128) - big ram + big rom - internal peripherals... Actuallly I must finish ZX projects: K-MOUSE 2011, complette RGBVGA convertor, ULA1 clone (zx clone based on old russian chil ULA1). After it I can continue on SAM projects... VELESOFT
Re: Resistor R55
Some years ago I work on ZX ULA clone: http://velesoft.speccy.cz/cpld128ula.JPG More tech information about ASIC I have on papers and in my head :) It's not so hard for implement with modern hardware :) Some parts of ASIC clone projects exist as my old sources, but I must all rewrite. Color palette will in external sram memory, CPLD will contain only logic and paging ports. VL1772 can be replaced later }with external coprocessor... About ASIC code - I write all in ABEL language, it's not VHDL source. I will rewrite all parts of ASIC to schematic for Eagle... after finish code. Source development is very fast (some days/one week), and next time will used for fixing bugs... VELESOFT - Original Message - To: sam-users@nvg.ntnu.no; VELESOFT Sent: Saturday, October 08, 2011 5:14 PM Subject: Re: Resistor R55 Look forward to seeing more on this. What status are you at with the ASIC module? Are you looking at replacing the 1772 as well? Any plans to make the ASIC code available - as it may allow others to help with your development perhaps? Quoting VELESOFT - Original Message - From: Leszek Chmielewski To: sam-users@nvg.ntnu.no Sent: Tuesday, October 04, 2011 11:11 AM Subject: Re: Resistor R55 My SAM has no BRIGHT too. There was a shortcut between Composite and +12V, so the MC1377P was burned out (Just got a replacement by desoldering a Atari Mega STE), I lost BRIGHT too as the ASIC was toasted a little too. After replacing it with ASIC from my spare SAM the BRIGHT is back again. It is time to design a replacement ASIC. Velesoft is working on one since years, but he is too ambitious: 4096 Colours, Hardware sprites and scrolling... LCD Hi. My project is SAM COUPE clone (but no ASIC replacement). First prototype will based on big CPLD + fast Z80cpu + big sram + saa1099 sound chip. Here is components for first SAM clone: http://velesoft.speccy.cz/other/ula-xc95288xl.jpg http://velesoft.speccy.cz/IMGP3176.JPG http://velesoft.speccy.cz/IMGP3178.JPG Priorities: - compatibility with SAM COUPE - more colours (minimal 256 colors palette) - faster CPU - possibility run at full speed 6MHz in all graphic modes (not contended memory) - better compatibility with ZX Spectrum (ZX mode can work as ZX128) - big ram + big rom - internal peripherals... Actuallly I must finish ZX projects: K-MOUSE 2011, complette RGBVGA convertor, ULA1 clone (zx clone based on old russian chil ULA1). After it I can continue on SAM projects... VELESOFT
Re: Resistor R55
On 03/10/11 23:40, Andrew Collier wrote:
On 3 Oct 2011, at 16:22, Thomas Harte wrote:
It looks like a previous owner of my current SAM has had occasion
to replace resistor R55, or at least, to solder an additional copy
of R55 on top of the existing one. See
http://postimage.org/image/1g4kbz490/
Immediate follow-on questions, mostly resulting from me being an
electrical dunce, are: what does R55 do, what would be the likely
effect if it was a bit dodgy and is it really okay just to solder
an extra resistor on top of an existing one?
According to the schematics in the tech manual, R55 is doing
something to do with the MIC tape interface, and should be a 100kΩ
resistor - which if I'm reading the photo correctly (the colour bands
look {brown, black, yellow, gold}) is exactly what it is.
Two of them wired in parallel are equivalent to a single resistor of
50kΩ (assuming they both work) though I'm not certain what the
implication of that is for the rest of the circuit.
R55 and C28 form a feedback circuit that should square up the audio
signal coming from the tape cassette. Reducing R55 from 100K to 50K, by
putting two in parallel, will increase the amount of feedback.
The Bright signal is generated by the ASIC and appears on pin 18 (If I
read my diagram correctly). It then goes to R65, R69 and R73 (all 36K
[orange, blue, orange stripes]) to drive each of the colour driver
transistors M3(green), M4(red) and M5(blue) (3x BC547).
If you have lost bright on one colour look at the corresponding resistor
and PCB connections. If the transistor has blown you would lose that
colour completely. If you have no bright on any colour then check the
output of the ASIC and the PCB connections from there to the 3 resistors
for cracks, dry joints, broken through plating etc.
If there is no signal coming out of the ASIC then get used to a dull
life. :-(
Nev
Re: Resistor R55
2011/10/4 nev young pasiphae1...@yahoo.co.uk
On 03/10/11 23:40, Andrew Collier wrote:
On 3 Oct 2011, at 16:22, Thomas Harte wrote:
It looks like a previous owner of my current SAM has had occasion
to replace resistor R55, or at least, to solder an additional copy
of R55 on top of the existing one. See
http://postimage.org/image/1g4kbz490/
Immediate follow-on questions, mostly resulting from me being an
electrical dunce, are: what does R55 do, what would be the likely
effect if it was a bit dodgy and is it really okay just to solder
an extra resistor on top of an existing one?
According to the schematics in the tech manual, R55 is doing
something to do with the MIC tape interface, and should be a 100kΩ
resistor - which if I'm reading the photo correctly (the colour bands
look {brown, black, yellow, gold}) is exactly what it is.
Two of them wired in parallel are equivalent to a single resistor of
50kΩ (assuming they both work) though I'm not certain what the
implication of that is for the rest of the circuit.
R55 and C28 form a feedback circuit that should square up the audio
signal coming from the tape cassette. Reducing R55 from 100K to 50K, by
putting two in parallel, will increase the amount of feedback.
The Bright signal is generated by the ASIC and appears on pin 18 (If I
read my diagram correctly). It then goes to R65, R69 and R73 (all 36K
[orange, blue, orange stripes]) to drive each of the colour driver
transistors M3(green), M4(red) and M5(blue) (3x BC547).
If you have lost bright on one colour look at the corresponding resistor
and PCB connections. If the transistor has blown you would lose that
colour completely. If you have no bright on any colour then check the
output of the ASIC and the PCB connections from there to the 3 resistors
for cracks, dry joints, broken through plating etc.
If there is no signal coming out of the ASIC then get used to a dull
life. :-(
Nev
My SAM has no BRIGHT too. There was a shortcut between Composite and +12V,
so the MC1377P was burned out (Just got a replacement by desoldering a Atari
Mega STE), I lost BRIGHT too as the ASIC was toasted a little too. After
replacing it with ASIC from my spare SAM the BRIGHT is back again.
It is time to design a replacement ASIC. Velesoft is working on one since
years, but he is too ambitious: 4096 Colours, Hardware sprites and
scrolling...
LCD
Re: Resistor R55
I hadn't considered that bright might be variable by channel — I'll
have to check that out.
If it were MC1377P affecting all channels then presumably I'd see the
effect only through the aerial or a single-line video output? If I
were to find a suitable RGB scart cable then I'd still get the
expected output?
Re: the ASIC and primarily because I'm curious, how would making a
replacement for that work? Are there readily available FPGAs that
could drop straight into the same slot, if not then how expensive is
it to build some sort of bridge? As I said, I'm quite an electrical
dunce so don't hesitate to be patronising.
Given that at least some of my bright comes and goes, my floppy drive
seems to be dead (it makes a spinning noise and lights up but fails to
report that a disk is inserted) and there's a real chance I may
emigrate soon it might be time for me to put my real SAM away for
good. That'd be a little sad.
On Tue, Oct 4, 2011 at 10:11 AM, Leszek Chmielewski retr...@gmail.com wrote:
2011/10/4 nev young pasiphae1...@yahoo.co.uk
On 03/10/11 23:40, Andrew Collier wrote:
On 3 Oct 2011, at 16:22, Thomas Harte wrote:
It looks like a previous owner of my current SAM has had occasion
to replace resistor R55, or at least, to solder an additional copy
of R55 on top of the existing one. See
http://postimage.org/image/1g4kbz490/
Immediate follow-on questions, mostly resulting from me being an
electrical dunce, are: what does R55 do, what would be the likely
effect if it was a bit dodgy and is it really okay just to solder
an extra resistor on top of an existing one?
According to the schematics in the tech manual, R55 is doing
something to do with the MIC tape interface, and should be a 100kΩ
resistor - which if I'm reading the photo correctly (the colour bands
look {brown, black, yellow, gold}) is exactly what it is.
Two of them wired in parallel are equivalent to a single resistor of
50kΩ (assuming they both work) though I'm not certain what the
implication of that is for the rest of the circuit.
R55 and C28 form a feedback circuit that should square up the audio
signal coming from the tape cassette. Reducing R55 from 100K to 50K, by
putting two in parallel, will increase the amount of feedback.
The Bright signal is generated by the ASIC and appears on pin 18 (If I
read my diagram correctly). It then goes to R65, R69 and R73 (all 36K
[orange, blue, orange stripes]) to drive each of the colour driver
transistors M3(green), M4(red) and M5(blue) (3x BC547).
If you have lost bright on one colour look at the corresponding resistor
and PCB connections. If the transistor has blown you would lose that
colour completely. If you have no bright on any colour then check the
output of the ASIC and the PCB connections from there to the 3 resistors
for cracks, dry joints, broken through plating etc.
If there is no signal coming out of the ASIC then get used to a dull
life. :-(
Nev
My SAM has no BRIGHT too. There was a shortcut between Composite and +12V,
so the MC1377P was burned out (Just got a replacement by desoldering a Atari
Mega STE), I lost BRIGHT too as the ASIC was toasted a little too. After
replacing it with ASIC from my spare SAM the BRIGHT is back again.
It is time to design a replacement ASIC. Velesoft is working on one since
years, but he is too ambitious: 4096 Colours, Hardware sprites and
scrolling...
LCD
Re: Resistor R55
Am 04.10.2011 17:32, schrieb Thomas Harte:
I hadn't considered that bright might be variable by channel — I'll
have to check that out.
If it were MC1377P affecting all channels then presumably I'd see the
effect only through the aerial or a single-line video output? If I
were to find a suitable RGB scart cable then I'd still get the
expected output?
MC1377P mixes RGB to composite video, so if it is dead, you wont see any
picture on composite output, but all is looking normal on RGB output. If
you have no bright, but composite video is otherwise okay, then MC1377P
is okay.
Re: the ASIC and primarily because I'm curious, how would making a
replacement for that work? Are there readily available FPGAs that
could drop straight into the same slot, if not then how expensive is
it to build some sort of bridge? As I said, I'm quite an electrical
dunce so don't hesitate to be patronising.
I think, the supply voltages are maybe on different pins, and different
levels (Modern FCGA chips use often 3.3 Volt or less, but SAM has 5
Volt). If so, there will be no drop in replacement
Using SMD technology it would still be possible to create a drop-in
board with powerful chip that can act as relpacement for the ASIC.
Given that at least some of my bright comes and goes, my floppy drive
seems to be dead (it makes a spinning noise and lights up but fails to
report that a disk is inserted) and there's a real chance I may
emigrate soon it might be time for me to put my real SAM away for
good. That'd be a little sad.
Check how stable the voltage from your transformator is, maybe one of
the capacitors is dried out.
I just ordered a SAM drive board without the WD1772 controller (I still
have some working controllers desoldered from old Ataris ST, these are
very cheap on eBay) and drive from samcoupe.com I think, your problem is
the drive too, not the controller, as mine is.
LCD
On Tue, Oct 4, 2011 at 10:11 AM, Leszek Chmielewskiretr...@gmail.com wrote:
2011/10/4 nev youngpasiphae1...@yahoo.co.uk
On 03/10/11 23:40, Andrew Collier wrote:
On 3 Oct 2011, at 16:22, Thomas Harte wrote:
It looks like a previous owner of my current SAM has had occasion
to replace resistor R55, or at least, to solder an additional copy
of R55 on top of the existing one. See
http://postimage.org/image/1g4kbz490/
Immediate follow-on questions, mostly resulting from me being an
electrical dunce, are: what does R55 do, what would be the likely
effect if it was a bit dodgy and is it really okay just to solder
an extra resistor on top of an existing one?
According to the schematics in the tech manual, R55 is doing
something to do with the MIC tape interface, and should be a 100kΩ
resistor - which if I'm reading the photo correctly (the colour bands
look {brown, black, yellow, gold}) is exactly what it is.
Two of them wired in parallel are equivalent to a single resistor of
50kΩ (assuming they both work) though I'm not certain what the
implication of that is for the rest of the circuit.
R55 and C28 form a feedback circuit that should square up the audio
signal coming from the tape cassette. Reducing R55 from 100K to 50K, by
putting two in parallel, will increase the amount of feedback.
The Bright signal is generated by the ASIC and appears on pin 18 (If I
read my diagram correctly). It then goes to R65, R69 and R73 (all 36K
[orange, blue, orange stripes]) to drive each of the colour driver
transistors M3(green), M4(red) and M5(blue) (3x BC547).
If you have lost bright on one colour look at the corresponding resistor
and PCB connections. If the transistor has blown you would lose that
colour completely. If you have no bright on any colour then check the
output of the ASIC and the PCB connections from there to the 3 resistors
for cracks, dry joints, broken through plating etc.
If there is no signal coming out of the ASIC then get used to a dull
life. :-(
Nev
My SAM has no BRIGHT too. There was a shortcut between Composite and +12V,
so the MC1377P was burned out (Just got a replacement by desoldering a Atari
Mega STE), I lost BRIGHT too as the ASIC was toasted a little too. After
replacing it with ASIC from my spare SAM the BRIGHT is back again.
It is time to design a replacement ASIC. Velesoft is working on one since
years, but he is too ambitious: 4096 Colours, Hardware sprites and
scrolling...
LCD
Re: Resistor R55
If the original R55 has blown, i.e no current is able to pass through it, then the piggy backed R55 will restore the circuit as intended. If the piggy-backed one has blown as well I'd be concerned as to what is causing this to happen!
Re: Resistor R55
Thomas Harte wrote: It looks like a previous owner of my current SAM has had occasion to replace resistor R55, or at least, to solder an additional copy of R55 on top of the existing one. See http://postimage.org/image/1g4kbz490/ That's something I've seen on a lot of SAM motherboards by soldering another idential resistor on top (in parallel) the resistance in the circuit is halved. But, i've never actually bothered to see where in the circuit R55 lines to see why they wanted to reduce it... Colin = Quazar : Hardware, Software, Spares and Repairs for the SAM Coupé 1995-2011 - Celebrating 17 Years of developing for the SAM Coupé Website: http://www.samcoupe.com/
Re: Resistor R55
On 3 Oct 2011, at 16:22, Thomas Harte wrote:
It looks like a previous owner of my current SAM has had occasion to
replace resistor R55, or at least, to solder an additional copy of R55
on top of the existing one. See http://postimage.org/image/1g4kbz490/
Immediate follow-on questions, mostly resulting from me being an
electrical dunce, are: what does R55 do, what would be the likely
effect if it was a bit dodgy and is it really okay just to solder an
extra resistor on top of an existing one?
According to the schematics in the tech manual, R55 is doing something to do
with the MIC tape interface, and should be a 100kΩ resistor - which if I'm
reading the photo correctly (the colour bands look {brown, black, yellow,
gold}) is exactly what it is.
Two of them wired in parallel are equivalent to a single resistor of 50kΩ
(assuming they both work) though I'm not certain what the implication of that
is for the rest of the circuit.
(R61 to R75 look like they are something to do with video generation).
Andrew
