Gold Fish Zeddy
Gold Fish Zeddy
Right...
As I mentioned earlier, I dug my shiny Issue 1 zeddy out and set it up with an old telly.
I was having a frustrating time tuning it in so I did a quick trawl and found the transistor - resistor composite mod.
Almost identical mod to the speccy one so I carried it out and hey presto a half decent image.
The keyboard is fully working... almost smug at this point
'K' cursor at the ready I typed in 10 Print "Hello World";
and.... it printed hello world!! no retention of the program... I let it go cold and tried again... nothing.
I've been round the board tidying up suspicious solder joints.
I'm guessing I've part blown the ULA
Is this a known curable fault or do I need a new zeddy??? I'm guessing ULAs are scarce....
Any help gratefully anticipated
As I mentioned earlier, I dug my shiny Issue 1 zeddy out and set it up with an old telly.
I was having a frustrating time tuning it in so I did a quick trawl and found the transistor - resistor composite mod.
Almost identical mod to the speccy one so I carried it out and hey presto a half decent image.
The keyboard is fully working... almost smug at this point
'K' cursor at the ready I typed in 10 Print "Hello World";
and.... it printed hello world!! no retention of the program... I let it go cold and tried again... nothing.
I've been round the board tidying up suspicious solder joints.
I'm guessing I've part blown the ULA
Is this a known curable fault or do I need a new zeddy??? I'm guessing ULAs are scarce....
Any help gratefully anticipated
Re: Gold Fish Zeddy
Hi Marcus,
When you say the program was not retained....
Do you mean that you entered:
10 PRINT "HELLO WORLD"
RUN
LIST
and there was no program there?
Or did you forget to enter the command LIST (which means list the program)?
When you say the program was not retained....
Do you mean that you entered:
10 PRINT "HELLO WORLD"
RUN
LIST
and there was no program there?
Or did you forget to enter the command LIST (which means list the program)?
Rich Mellor
RWAP Software
RWAP Adventures
SellMyRetro
Retro-Printer Module
Also Involved in:
Icephorm
RWAP Software
RWAP Adventures
SellMyRetro
Retro-Printer Module
Also Involved in:
Icephorm
Re: Gold Fish Zeddy
Hi
It executes immediately, as though there was no line number enteredWhen you say the program was not retained....
- 1024MAK
- Posts: 5118
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: Gold Fish Zeddy
Strange...
What about if you enter
Does that get stored?
It does not sound like a ULA fault. More likely suspects are:
What about if you enter
Code: Select all
1 REM TEST
It does not sound like a ULA fault. More likely suspects are:
- RAM (have you got an external RAM pack to test with?)
- ROM
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
Re: Gold Fish Zeddy
Hi Mark
'1 REM TEST ' no it just flags 0/0
RAM (have you got an external RAM pack to test with?)
Yes, I've just tried my MEMOPAK 16k and its working... phew
The little chap is starting to remember the lines as entered
There are a few 'bits' flashing randomly around the screen that disappear when I gently press the ULA
Wow this gets hot rapidly
'1 REM TEST ' no it just flags 0/0
RAM (have you got an external RAM pack to test with?)
Yes, I've just tried my MEMOPAK 16k and its working... phew
The little chap is starting to remember the lines as entered
There are a few 'bits' flashing randomly around the screen that disappear when I gently press the ULA
Wow this gets hot rapidly
- 1024MAK
- Posts: 5118
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: Gold Fish Zeddy
Yes, the ULAs do run hot.
With the power disconnected, if the ULA is in a socket, carefully using a blunt flat knife, or a suitable flat bladed screwdriver, gently lift one end of the ULA. But only about 2 to 3mm. Then do the same at the other end of the chip. Repeat so that the chip is gradually eased out. Don't let the knife or screwdriver press into the PCB or the tracks could be damaged. As the chip becomes more free, hold a finger or thumb on top to prevent it moving too far when the socket finally lets go. If you don't do this, the chip will move suddenly and then some of the pins will bend and may break off when you try to straighten them.
Once out, clean the pins. Check that the socket contacts all look the same. Then carefully put the ULA back in. It's also worthwhile checking the solder joints on the underside of the circuit board. If you see any poorly made joints or dry joints, then the joint needs to be resoldered.
Mark
With the power disconnected, if the ULA is in a socket, carefully using a blunt flat knife, or a suitable flat bladed screwdriver, gently lift one end of the ULA. But only about 2 to 3mm. Then do the same at the other end of the chip. Repeat so that the chip is gradually eased out. Don't let the knife or screwdriver press into the PCB or the tracks could be damaged. As the chip becomes more free, hold a finger or thumb on top to prevent it moving too far when the socket finally lets go. If you don't do this, the chip will move suddenly and then some of the pins will bend and may break off when you try to straighten them.
Once out, clean the pins. Check that the socket contacts all look the same. Then carefully put the ULA back in. It's also worthwhile checking the solder joints on the underside of the circuit board. If you see any poorly made joints or dry joints, then the joint needs to be resoldered.
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
Re: Gold Fish Zeddy
If the ULA is socketed - remove it and push it back in (whilst the ZX81 is off of course!) in case there is a build up on the legs...
I have 6116 RAM chips on sellmyretro.com if you want to replace the internal RAM, but there is no need if you are going to use the external RAM pack - it might just need the RAM re-soldering
I have 6116 RAM chips on sellmyretro.com if you want to replace the internal RAM, but there is no need if you are going to use the external RAM pack - it might just need the RAM re-soldering
Rich Mellor
RWAP Software
RWAP Adventures
SellMyRetro
Retro-Printer Module
Also Involved in:
Icephorm
RWAP Software
RWAP Adventures
SellMyRetro
Retro-Printer Module
Also Involved in:
Icephorm
Re: Gold Fish Zeddy
The ULA is soldered to the PCB
Re: Gold Fish Zeddy
I've just re-soldered all joints on the underside. No change to the random screen bits flashing.
Now I'm about to change the 2 electrolytic caps
Now I'm about to change the 2 electrolytic caps
Re: Gold Fish Zeddy
I changed the caps and added a heatsink to the ULA
It now seems to be operating without the screen artifacts
I'll swap the 7805 for a switch mode unit so I can stop burning myself on the glowing heatsink.
Then I can give it a soak test.
Thanks for the pointers
It now seems to be operating without the screen artifacts
I'll swap the 7805 for a switch mode unit so I can stop burning myself on the glowing heatsink.
Then I can give it a soak test.
Thanks for the pointers