CRT H-size - Page 1
Forum section: electronics / beginners

author: fabiodl
author_rank: Frequent Contributor
timestamp: May 23, 2021, 08:47:07 am
content: I havethis CRT tvwhich I'd like to use formister(yes, I am well aware of the dangers of CRTs' high voltage. I mess around with crts since I was 12 and I am still alive).I RGB modded it by replacing the OSD (this is the chip used for video selection).I have however a problem. The image is cropped on the sides.I could enter the service menu usingthis key combinationbut the only geometry related options areV-POS,H-POS and V-HET (which corresponds to the veritical size).This seems common.this postis noticing width tuning is missing on another panasonic tv (TH-21FA8). Same inthis reddit post.First, I wonder why it is "more difficult" to adjust the horizontal width then the vertical height.Second is there any hardware mod that could be done to change the width (I imagine adding a pot somewhere) ?This is the closest TV I found the manual of.Alternatively there is a submenu named "opt". According tothis articleit is " for adjustment at the plant. Stay away from this item, as it means adjustment of all items." but I cannot enter it. Does anyone know how to from experience on similar tvs?

author: PKTKS
author_rank: Super Contributor
timestamp: May 25, 2021, 02:07:19 pm
content: Quote from: fabiodl on May 23, 2021, 08:47:07 amFirst answer:- Horizontal sweep is designed to be phase locked by the incomingsignal - which is **ALL** horizontal frequency based.- Usually the vertical sweep is synch'ed by integrating the horizontalpulses (equalizing train inside the vertical blank..)- That signal will also provide synch to the FLYBACK in whichthe horizontal scan isthe primarysignal.- Vertical is piece of cake - horizontal is not - because it is tied to the FLYBACKSecond answer mostly overlaps the first.messing the horizontal sweep will undoubtedly mess the FLYBACK PSUin which you need a great care to not blow anything...OLD... circuits before these large integrated w/OSD stuff..usually have auxiliary coils on the collar/yoke mostly to correctconvergence but also to adjust cushion and size of screen..new stuff is too way cheap for that..And THAT stuff w/VCR inside is way too self oriented for thatPaul

author: PKTKS
author_rank: Super Contributor
timestamp: May 25, 2021, 02:17:57 pm
content: Checked the manual provided..YES anyone trying to change that will have a hard time...The mains PSU is a "modern" switched mode standaloneone and the FLYBACK is totally separated having dedicatedintegrated (digitally generated) stages..Cheap highly consumer oriented stuff..Not suited to be modded although possible...Unworthy the time effort.Paul

author: fabiodl
author_rank: Frequent Contributor
timestamp: May 26, 2021, 11:41:19 am
content: Quote from: PKTKS on May 25, 2021, 02:07:19 pmThank you very much. You state it is phase locked. Is only the phase adjusted or the frequency as well? I am thinking about editing the sync pulse generation on the FPGA to get a longer sync pulse. Would that do the trick?Quote from: PKTKS on May 25, 2021, 02:17:57 pmWhen modding it, I definitely had this impression. The tube itself may be not that bad though.

author: PKTKS
author_rank: Super Contributor
timestamp: May 26, 2021, 03:24:23 pm
content: Quote from: fabiodl on May 26, 2021, 11:41:19 amThat changed quite a bit along the first B&W models all TUBEbased ... then to NTSC/PAL signals all transistor... then...this kind of highly integrated digitally processed signals..The Horizontal sweep always had a free run local oscillatorwhich would be synch'ed w/the incoming broadcastedsignal .. or run free when no locking carrier...That oscillator in the old times could be adjusted as well...Introduction of NTSC/PAL sub carriers also introducedXTAL oscillators - multiple of the Horizontal sweep.Several variants exists and the digital ones do a hellof a mess producing the "local horizontal" signal back.This model incorporates a VCR in which the HEAD(s) signalis also XTAL controlled.. it would require a detail view ofhow they are being generated...It seem the FLYBACK is just "drived" by that huge video ICprocessor.. hard to say if you can externally adjust the signal..IMHO? not worthy - simple models would be easier than that.all circuitry is more or less connected in this model...Paul