Search found 10 matches

by dac
Sat Jul 31, 2021 8:59 pm
Forum: ZX Spectrum Lounge
Topic: Harlequin video modifications
Replies: 40
Views: 41104

Re: Harlequin video modifications

Yes, you are right: original resistors values give the best image.

For RGB CSYNC I omitted R48, R49, C35 and changed R18 from 270 to 1K, that gives a CSYNC amplitude of 0.3V.
by dac
Sat Jul 31, 2021 8:51 pm
Forum: ZX Spectrum Lounge
Topic: Harlequin strange video artefact
Replies: 0
Views: 1194

Harlequin strange video artefact

I'll do my best to describe it:
If paper 0 (black) meets right border, then on the left border appears a grey, half pixel wide line.
If similar ink 0 meets right border, nothing appears on the left side.
IMG_0497.jpg
IMG_0499.jpg
IMG_0498.jpg
Has anyone seen this behaviour before?
by dac
Wed Jul 14, 2021 9:20 pm
Forum: ZX Spectrum Lounge
Topic: Harlequin video modifications
Replies: 40
Views: 41104

Re: Harlequin video modifications

It goes to GND on my PCB. All it does is insignificantly lowering the sync voltage (by almost doubling Q1 Ic current).
by dac
Wed Jul 14, 2021 7:55 pm
Forum: ZX Spectrum Lounge
Topic: Harlequin video modifications
Replies: 40
Views: 41104

Re: Harlequin video modifications

Does anyone know the purpose of R48 (270 ohm)? It connects Q1 emitter to the ground and is in fact in parallel to R18 + 75 ohm (from TV).
It seems pointless to me...
by dac
Tue Jul 13, 2021 8:21 pm
Forum: ZX Spectrum Lounge
Topic: Harlequin video modifications
Replies: 40
Views: 41104

Re: Harlequin video modifications

Alternatively, one might try replacing those 18k resistors with 13k ones (instead of adding 47k in paralel).
by dac
Tue Jul 13, 2021 8:03 pm
Forum: ZX Spectrum Lounge
Topic: Harlequin video modifications
Replies: 40
Views: 41104

Re: Harlequin video modifications

It seems that three 47k resistors soldered in paralel with each of the 18k resistors (R23, R26, R29 Harlequin 128k) would do the trick! (and replacing three 68 ohm resistors with 75 ohm ones - R34, R38, R43) Since my Harlequin is not complete yet, can anyone test this before I do, and provide some p...
by dac
Fri Jul 09, 2021 11:40 am
Forum: ZX Spectrum Lounge
Topic: Harlequin video modifications
Replies: 40
Views: 41104

Re: Harlequin video modifications

For example, changing resistors R34, R19, R20, R38, R21, R43 from 68 ohm to 75 ohm, and adding 3 x 56k resistors in paralel to 18k resistors R23, R26, R29 should give a bright voltage of 0.701V and a normal voltage of 0.467V, for a ratio of 0.667. I will test this in near future and come back with r...
by dac
Fri Jul 09, 2021 9:59 am
Forum: ZX Spectrum Lounge
Topic: Harlequin video modifications
Replies: 40
Views: 41104

Re: Harlequin video modifications

What do you think about normal colour / bright colour voltage levels? Watching various clips and pictures online, it seems to me that the contrast between normal blue and bright blue is too low. According to schematics, bright blue voltage across the 75 ohm resistor is about 0.700V, while normal blu...
by dac
Thu Jul 08, 2021 3:14 pm
Forum: ZX Spectrum Lounge
Topic: Harlequin video modifications
Replies: 40
Views: 41104

Re: Harlequin video modifications

Well, there might be some timing difference between CSYNC and LUMA sync, therefore some different horizontal alignment between those 2 cases (one might work better than the other with different displays). I used to sync SCART RGB with composite video, but doing so, the chrominance subcarrier (4.433 ...
by dac
Thu Jul 08, 2021 9:13 am
Forum: ZX Spectrum Lounge
Topic: Harlequin video modifications
Replies: 40
Views: 41104

Re: Harlequin video modifications

Hello everybody!

I can’t help but thinking that the original intention was to provide two possibilities for RGB syncing: either CSYNC, or LUMA signals (and the PCB has a mistake connecting that trace to CHROMA), but not both at the same time!