Pet 8296 blown fuse with monitor connected, and no chirp sound

[demonlg]

An idea came to me, tell me if it's crazy or is it possible in some way, I checked the faulty PROM and confirm what was reported in the videos previous to this post, I then checked PIN 9 of UC2 and saw that the signal is correct but for 40 columns reported on schematic diagram jumpers J3 and J4 attached, it has two negative pulses with a different frequency instead of just one negative pulse i aspected, I could somehow take the output signal from PIN 9 of UC2 and transform it into what I would need for 80 columns which should I have it on PIN 7 of UC2?

 

[demonlg]

This is the signal on PIN 9 of UC2

 

[daver2]

That is pretty conclusive.

I assume that the inputs A-E look the same?

Dave

 

[daver2]

I suspect (internally) that the logic for the output pins 7 and UC2 are somehow 'intermingled'.

Internally, pin 9 will be whatever is on pin 7 divided by 2.

It is easier with logic to divide by 2 than to multiply a frequency by 2...

Dave

 

[demonlg]

I suspect (internally) that the logic for the output pins 7 and UC2 are somehow 'intermingled'.

Yes, seem to be intermittent signal.

Internally, pin 9 will be whatever is on pin 7 divided by 2.

Yes

It is easier with logic to divide by 2 than to multiply a frequency by 2...

Ok, in this case i have to divide or moltiplicate signal on PIN 9?

Dave

 

[demonlg]

That is pretty conclusive.

I assume that the inputs A-E look the same?

Yes all are the same, onli UC2 PIN 7 are wrong!

Dave

 

[daver2]

>>> Ok, in this case i have to divide or moltiplicate signal on PIN 9?

You have to MULTIPLY the frequency of pin 9 by 2 to give the same as on pin 7. I.e. the difficult solution!

See if there is anyone local to you on VCFED who may be able to program a '288 for you.

Dave

 

[demonlg]

Where?

 

[demonlg]

I have found this adapter online, is possible to working for you?

http://www.zaccaria-pinball.com/mrgame/video.html

 

[daver2]

>>> Where?

On the VCFED "Vintage Computer Services Offered/Needed" forum.

As for the adapter, I wouldn't know. It all depends upon your EPROM programmer. You can try it... You may destroy the '288 you are trying to program or even destroy your EPROM programmer...

It could also be possible that it may take a few attempts to understand how to program the '288. Once you have attempted to program a '288 (and it goes wrong) it is toast... If you have bought two (2) blank parts - you have one failed attempt...

Your choice.

Dave

 

[demonlg]

Hi Dave,

this is not an adapter used for programming 74s288 but it is an adapter to use a simple 2516/2716 in the place of original 74s288.

 

[daver2]

I am not sure a 2716 is going to be fast enough... Is it?

Dave

 

[demonlg]

I don't know too, but in the link author reports yes on a Zaccaria pinball, i have made now the adapter, tomorrow i burn old 2516 and try, if it working is a good solution for now.

The adapter is orrible now but, it is a first and on a multi hole board, but connections are good and coresponding to table in the link (i have fitted 2532 only for the photo).

I update you tomorrow.

 

[daver2]

The data sheets for the '288 and 2716 you are using will tell you.

Dave

 

[demonlg]

First test, machine boot with chirp and monitor receive vdata e video, and glow but no character on screen, with chip totally removed the machine not boot anymore and not chirp, i try with different type of eprom.

I have to check signals now if is all present and correct or not.

 

[daver2]

A DM74S288 has an access time of 25 ns.

A 2716 EPROM has (at best) a 250 ns access time. An order of magnitude too slow...

There is no guarantee that the 25 ns is actually required - and it may be relaxed - but whether you could use something as slow as a 2716 in this machine is debatable.

If the pinball machine had a slow-speed requirement, then this might work.

Dave

 

[demonlg]

Second test, i have burned a ST2716 market as FAST on top, with this the machine boot, i have Commodore screen and ready but with cursor in a wrong position, is all to the right of ready and i have a blank square in the bottom right corner, keyboard working and machine respond to the command but cursor stays in the right.

With all other type of 2716 or 2516 the machine not boot or boot with garbage, but cheeper is present and correct.

This is confirm the speed problem of EPROM, i make other test with this fast 2716 model, i have to check if the adapter made is ok or not.

I have also 2732-45ns but i don't kwnow if i made modify on the adapter for this.

 

[daver2]

If it is a -45 EPROM it is actually 450 ns.

Please check the data sheets for the parts to determine the actual parameters from the part numbers.

Dave

 

[demonlg]

Yes i have readed 450ns.....

 

[demonlg]

This is the model with machine boot with the cursor problem.