Search found 2936 matches

by exxos
Tue Sep 18, 2018 6:15 pm
Forum: STF REMAKE PROJECT
Topic: ALPHA MODIFICATIONS
Replies: 26
Views: 450

Re: ALPHA MODIFICATIONS

BR PULL UP FIX

Bodge wire 1... Wire the thick yellow drawn wire as shown on the back of the pcb...

(Fixing missing pull up resistor on BR).

bw1.jpg
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by exxos
Tue Sep 18, 2018 6:12 pm
Forum: ALPHA USER BUILDS
Topic: Icky - Progress
Replies: 33
Views: 283

Re: Icky - Progress

OK.. "bodge wire 1" time...

bw1.jpg
bw1.jpg (278.2 KiB) Viewed 56 times
by exxos
Tue Sep 18, 2018 6:07 pm
Forum: ALPHA USER BUILDS
Topic: Forgottenmyname - Progress
Replies: 31
Views: 263

Re: Forgottenmyname - Progress

Forgottenmyname wrote:
Tue Sep 18, 2018 6:01 pm
Just the rising voltage problem on the data lines etc now
I'm not really following what you mean there... voltage on the buses should rise up to 5V unless the CPU sets it to 0V... voltage could be anything in between cycles, can appear like a 2V triangle etc.
by exxos
Tue Sep 18, 2018 6:05 pm
Forum: ALPHA USER BUILDS
Topic: Icky - Progress
Replies: 33
Views: 283

Re: Icky - Progress

hmmm.. I can't see a pull up on BR anywhere... so checking to see whats happened there...
by exxos
Tue Sep 18, 2018 6:02 pm
Forum: ALPHA USER BUILDS
Topic: Icky - Progress
Replies: 33
Views: 283

Re: Icky - Progress

Icky wrote:
Tue Sep 18, 2018 6:00 pm
BG and BGACK are high all the time but BR is low all the time
hmmm, AFAIK nothing should be requesting the bus during startup (other than DMA stuff, blitter, ) Even so, CPU isn't granting the bus to anything either.. so that is odd...
by exxos
Tue Sep 18, 2018 5:50 pm
Forum: ALPHA USER BUILDS
Topic: Forgottenmyname - Progress
Replies: 31
Views: 263

Re: Forgottenmyname - Progress

It makes me wonder to replace the composite transistor with a AND gate instead.. then also buffer the V&H sync though the same IC.. would need 3 gates and they normally have 4 . But would help protect and buffer the syncs and up the voltage on them... assuming thats the problem.. The syncs have diod...
by exxos
Tue Sep 18, 2018 5:33 pm
Forum: ALPHA USER BUILDS
Topic: Icky - Progress
Replies: 33
Views: 283

Re: Icky - Progress

Icky wrote:
Tue Sep 18, 2018 5:22 pm
BERR on CPU goes high 5v at start and stays there
What about BG, BGACK, BR ? All those should stay high all the time...
by exxos
Tue Sep 18, 2018 5:30 pm
Forum: ALPHA USER BUILDS
Topic: Forgottenmyname - Progress
Replies: 31
Views: 263

Re: Forgottenmyname - Progress

I might make a new cable with hsync and hsync. Would everything else be the same minus the comp sync obviously You should get near 5V from the GLUE on the sync then.. composite voltage might be a fraction to low.. I've seen it a lot before with sync faults on ST's... https://www.youtube.com/watch?f...
by exxos
Tue Sep 18, 2018 4:47 pm
Forum: ALPHA USER BUILDS
Topic: Forgottenmyname - Progress
Replies: 31
Views: 263

Re: Forgottenmyname - Progress

I did a quick simulation based on the 3904 & 337..

Basically the Atari 3904 outputs a tiny higher voltage, but not by much.. but could be enough to cause issues...

2.335V vs 2.397V.

I guess you could swap the BC337 out for the 2N3904 from a the donor ST board.. see if that helps...

s1.jpg
s1.jpg (77.52 KiB) Viewed 78 times
by exxos
Tue Sep 18, 2018 4:36 pm
Forum: ALPHA USER BUILDS
Topic: Forgottenmyname - Progress
Replies: 31
Views: 263

Re: Forgottenmyname - Progress

Probably the thing to do is check composite sync on a working ST and then the STF... it could just be the voltage is a fraction lower than the TV likes or something silly...