Search found 84 matches

by patters
Wed Apr 14, 2021 11:13 am
Forum: Hardware
Topic: Composite mod issue: left side of screen missing - solved!
Replies: 62
Views: 2292

Re: Composite mod issue: left side of screen missing - solved!

Thanks for taking the time to write that out, very detailed. One other observation I've noticed is that the remaining 10K trimmer seems to drift with temperature, or perhaps it's the ULA drifting as it warms up. The trimmer we removed seemed to set the duration of the back porch in the h-sync pulse....
by patters
Tue Apr 13, 2021 8:48 pm
Forum: Hardware
Topic: ZX-WESPI - add a cheap wifi-enabled fileserver to your Zeddy!
Replies: 12
Views: 789

Re: ZX-WESPI - add a cheap wifi-enabled fileserver to your Zeddy!

Thanks for the confirmation, I'll raise an issue on the project's GitHub.
by patters
Tue Apr 13, 2021 8:03 pm
Forum: Hardware
Topic: Composite mod issue: left side of screen missing - solved!
Replies: 62
Views: 2292

Re: Composite mod issue: left side of screen missing - solved!

I went back and re-watched the Joulespercoulomb video and according to him the black pixels should be at 0V which they're some way off on your oscilloscope traces. Is there an easy fix for that? Is that what the additional 1K resistor was aiming to fix? I notice that the circuit with your fixes is s...
by patters
Tue Apr 13, 2021 1:47 pm
Forum: Hardware
Topic: Diagnosing tape loading issues
Replies: 46
Views: 1731

Re: Diagnosing tape loading issues

Opened up my working Issue 1 to test:
ULA pin 20 to +5V = 1.737
ULA pin 20 to GND = 0.768

So the values are pretty consistent. Which is odd because it kind of suggests that the ULA circuitry on the defective Issue 3 should be ok.
by patters
Tue Apr 13, 2021 2:24 am
Forum: Hardware
Topic: ZX-WESPI - add a cheap wifi-enabled fileserver to your Zeddy!
Replies: 12
Views: 789

Re: ZX-WESPI - add a cheap wifi-enabled fileserver to your Zeddy!

I secured the WESPI board to the bottom case using a strip of adhesive hook and loop fastener which worked well. I like having it hidden inside. Wolf in sheep's clothing :D
by patters
Mon Apr 12, 2021 5:43 pm
Forum: Hardware
Topic: Diagnosing tape loading issues
Replies: 46
Views: 1731

Re: Diagnosing tape loading issues

Hang on, looks like I measured my resistances wrong. I didn't realise it would be directional, and it only works with the probes one way around. Is that because the connectivity to +5V and GND is going via a diode inside or upstream of the ULA? If I put the negative probe on the ULA pin 20, and with...
by patters
Mon Apr 12, 2021 12:49 am
Forum: Hardware
Topic: Diagnosing tape loading issues
Replies: 46
Views: 1731

Re: Diagnosing tape loading issues

I'm considering removing the ULA and socketing it, and then trying to buy a battered Zeddy on eBay to be a donor. Is this madness, or can it reasonably be removed - if for example I've previously managed to successfully remove the RAM chips without damage?
by patters
Sun Apr 11, 2021 1:31 am
Forum: Hardware
Topic: Diagnosing tape loading issues
Replies: 46
Views: 1731

Re: Diagnosing tape loading issues

My multimeter reads "1." for both when I do that, which is the same reading it gives when neither probe is touching anything, so I guess that means there is no short of pin 20.
by patters
Sun Apr 11, 2021 12:49 am
Forum: Hardware
Topic: Diagnosing tape loading issues
Replies: 46
Views: 1731

Re: Diagnosing tape loading issues

I have replaced C10. No change. R33 and R34 were measuring their correct resistances. All the continuity back to ULA pin 20 is fine. I used the test program linked above and it just detects zeros whatever is playing via EAR. I have replaced the 4K7 resistor at R33 for a 3K3 one and it made no differ...