TT issue / horizontal lines across the screen

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Chandler
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TT issue / horizontal lines across the screen

Postby Chandler » Fri Oct 05, 2012 10:01 am

i would love to repair my own personal TT

had this issue for years

it works ok but as the pictures show below these lines appear in all resolutions shortly after switching the machine on (worse in high res)

have changed the memory and PSU so far

Image

Image

AtariLikerMan0
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Re: TT issue / horizontal lines across the screen

Postby AtariLikerMan0 » Fri Oct 05, 2012 10:41 am

I suspect the ROM or a graphics chip. Unless you've got something special installed or get a buzz from mending old equipment, maybe a look at Ebay is the easiest fix.

The Atari isn't modular in construction so mending one was virtually always a specialist job.

Chandler
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Re: TT issue / horizontal lines across the screen

Postby Chandler » Fri Oct 05, 2012 12:14 pm

roms are fine

i have changed the C398082-001A U204 video shifter chip

same..

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Re: TT issue / horizontal lines across the screen

Postby nativ » Fri Oct 05, 2012 12:51 pm

Is it 'static' not changing ? or more of an 'interference' like analog tv reception?

I guess you tried different monitor and cables?
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Mark_G
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Re: TT issue / horizontal lines across the screen

Postby Mark_G » Fri Oct 05, 2012 12:52 pm

I got the same problem.

After checking, it was the monitor cable.

Before you investigate the computer, try the TT with another monitor.

Mark

Chandler
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Re: TT issue / horizontal lines across the screen

Postby Chandler » Fri Oct 05, 2012 3:14 pm

monitor is fine on anything else i plug into it

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Re: TT issue / horizontal lines across the screen

Postby Guest » Sat Oct 06, 2012 12:32 pm

what revision is it
rev a-c or d-k???
you can see at a glance if it has a soldered on 68030 or daughter boards and pga chips
its more likely the funnel ics as it 'looks' like a ram issue it will be a bad funnel for sure
i have a test cart for the TT i can mail to you once youve finished send it back
or if you look here viewtopic.php?f=27&t=19784
the rom images are there so you can use any atari diag cart and just if needed remake the blob shorts
there is also some pics of the guts of it


funnels are quite easy to change out if they are in sockets {rev a-c}
if not then youll need to use a hot air reflow or IR unit to remove them
and solder on some sockets

i think best charges the usual $45 for one
i 'think' i have a spare set somewhere

other than this carefully check around ram and funnel area for any shorts
i would also check the full data paths between the funnels and the TTVIDEO chip

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Re: TT issue / horizontal lines across the screen

Postby Chandler » Sat Oct 06, 2012 7:04 pm

hi Simbo

it's a rev H

so all SMT chips :(

i do actually have a TT test cart, how can i use the cart to test this area further before i remove the chips?

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Re: TT issue / horizontal lines across the screen

Postby Guest » Sun Oct 07, 2012 5:55 am

Chandler wrote:hi Simbo
it's a rev H
so all SMT chips :(
i do actually have a TT test cart, how can i use the cart to test this area further before i remove the chips?


do a ram test and a video test

the ram and video tests will show up whats wrong
changing the funnels youll need a reflow unit for sure
they are to big for LOWmelt
if you dont have one cost is less than 80 quid on ebay for latest KADA
you will need to get some nozzles

Guest

Re: TT issue / horizontal lines across the screen

Postby Guest » Sun Oct 07, 2012 3:59 pm

could be ???nah ??
maybe well it might be
try this take the main cable and some womens nail polisher sticks cut in two
clean all the connections inside it and the connections at the TT
and try replacing the mains switch on the TT
you may find this fixes it without unneeded surgery
this could just be mains crackle on the video signals from carbonized contacts
on the cable
you did say you changed out the psu
most often its the main cable and its the last thing people change
also check its plug perhaps a screw has vibrated loose on its connectors
still have the ideas of the funnels
it defo has a digital content to the hashing

i think my approach would be to use / borrow an oscilloscope
and check the 5V supply at the TTvideo and funnels etc ic;s

this can also be caused by a noisy capacitor {bi pass caps {decoupling on the ram and around the pcb}
sometimes a cap will sit and generate hash to the ic's vdd pin
can be hard to locate without a scope
to check for noisy vdd
ive found handy in the past and IR night scope

you can see at a glance a warm cap they get warm {resistance } then they produce hash
then one day they go BANG !!!! :contract:
and destroy the ram in your machine
i can vouch for this very problem with the machine frank B found for me and im upgading to 16/12 MB
if i remember it took out the DRAM and the FUNNELS
the ram was red hot and the funnels fried :wink:
viewtopic.php?f=27&t=19784
so watch out for that one!!!
c505 was the one that did in those ic's

one thing you didnt tell us chandler is is it there from boot
or just at gem ??? ie is the white screen white memory test etc chars/sprites clean ???

Chandler
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Re: TT issue / horizontal lines across the screen

Postby Chandler » Mon Oct 08, 2012 10:50 am

ok thanks for your help Simbo

psu and power cable are fine / changed both

the lines appear when it gets to GEM, not on memory test (i think) will cheack again and come back

and it seems to get worse as it warms up

PS: do you still burn TT tos roms simbo? i may be looking for a spare set of 3.06, can you give me a price?

:)

Guest

Re: TT issue / horizontal lines across the screen

Postby Guest » Mon Oct 08, 2012 11:25 am

hi kool
ill look and see if i have enough 90ns ones left
i have some 120ns ones already made up i think ill check
as the TT is in a state i can test them at the moment

so.. as for your TT if it gets worse with time and does not do it from boot
leave it on a while and try a cold boot see if they appear on the pre gem screen once its warm

in my view its either a duff cap or a gubbed funnel

see what the cart says??

Guest

Re: TT issue / horizontal lines across the screen

Postby Guest » Mon Oct 08, 2012 11:31 am

ok after a little thought i have arrived at some good advice

go to maplin and buy a can of 'freezer spray' get a pencil ready
then leave the machine on for a while till it get's worse

a bath towel is a handy thing to speed up the fault condition over the machine but not over the fan!!

then spray the funnels one at a time and the ram next
to find the duff ic or ic's and mark them {any ic you spray and the fault changes}

even caps ..! just a little of it goes a long way so dont go crazy you can damage ics by over spraying them

at least this will help narrow it down
Last edited by Guest on Mon Oct 08, 2012 12:02 pm, edited 3 times in total.

Guest

Re: TT issue / horizontal lines across the screen

Postby Guest » Mon Oct 08, 2012 11:36 am

ok i checked i have 6 90ns left

i dont have slower 010's and i owe a pair to another member for his tos 1.62

so ill set up the programmer and burn a set of 3.06 for you today
im at a loose end anyway i either do this or solder up my TT stram riser project
hopefully ill post them and a few other bits off tomorrow
some people have been very patient with me so i better get a grip

ill put them in the fridge now
£2 per ic £5 fee {bottle of wine for me}

8 + 5 +1post = £14 quid total
i only want payed when they arrive and your happy and they work etc
ill send my paypal details then ,,, :coffe:

Guest

Re: TT issue / horizontal lines across the screen

Postby Guest » Mon Oct 08, 2012 12:06 pm

another thing post your copy of gembench i will run the same test from my machine

this can be helpfull to see if there is a unit not working to the same level

perhaps others can also run the test on there TT and note discrepancies ¬¬

do you have TT ram fitted or more STRAM on a riser added if so remove it
and retest and post...

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Cyprian
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Re: TT issue / horizontal lines across the screen

Postby Cyprian » Mon Oct 08, 2012 12:46 pm

simbo2 wrote:another thing post your copy of gembench i will run the same test from my machine

this can be helpfull to see if there is a unit not working to the same level

perhaps others can also run the test on there TT and note discrepancies ¬¬

do you have TT ram fitted or more STRAM on a riser added if so remove it
and retest and post...



or Chandler can do test with NemBench and compare it with other users' results from that thread:
viewtopic.php?f=27&t=17970
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Re: TT issue / horizontal lines across the screen

Postby Guest » Mon Oct 08, 2012 2:10 pm

pm me an address to send the eproms to
ive burned and tested them etc...

Chandler
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Re: TT issue / horizontal lines across the screen

Postby Chandler » Fri Nov 02, 2012 8:19 pm

briefly using the TT today to test a scsi HD and i noticed that when i formatted the drive the lines almost went

then came back after format complete

i also get vertical lines too and it seems to start when it gets to desktop, while booting (mem test) not at all but i do get some randon vertical line flashing

Guest

Re: TT issue / horizontal lines across the screen

Postby Guest » Sat Nov 03, 2012 12:31 pm

i think your MCU could have an issue

Guest

Re: TT issue / horizontal lines across the screen

Postby Guest » Thu Nov 22, 2012 9:31 pm

ok
things to check
1 you need a scope {the good news is you can just use a sound card in the pc and a probe ... to its line it .. youll find free/payed software online for this }
2 you need to scope the vcc rails at the TTVIDEO and FUNNELS
to check for noisy bypass caps C201 202 {TTVIDEO chip} & c203 c206 {funnels}
3 you need a frequency counter to check ... or change the dot clock TTL crystal pack U203
they do drift with time .... and i would say can cause this very issue if its drifted more than a few dozen Hz

this is defo a data issue with either or funnels or TTVIDEO

the first sign i had to my TT RAM latest blow up was a bad video output but the ram was seen aok

till the cap finally failed

as i say took out my ram and 1 funnel ... not good !!! look for any of the yellow resin dipped ones
look atall brown or browning.... darker than others

i have replaced about 50 in my TT

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Re: TT issue / horizontal lines across the screen

Postby 1st1 » Fri Nov 23, 2012 6:57 am

This looks very the same as when I built my own memory extension years back for my ST. To me the problem appeared when I used a generic PCB where I had to make the traces by hand as a proof of concept before making a professional layout and etching it. With that prototype I already was able to almost fix the problem by adding more ground connections to the mainboard of the ST and adding some pullups to the adress and data lines, only a few such effects stayed with the prototype. The final PCB did not have that problem then.

So in my opinion this is definitively a memory timing problem while the alternate/parallel access of the (TT-)shifter and CPU to the ST memory. It could be that one or more of the DRAM chips got tooo slow for that duruing the years.

If you have an extension board for ST memory in your TT, try to remove that and look if the problem disappears with only 2 MB onboard. If that's ok, try another ST-RAM memory card. If that's ok, something must be wrong with your memory card, maybe you should send it to simbo2 to replace the 2 MB chips by some with 8 MB in total... viewtopic.php?f=27&t=24048
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