VHS VCRs with easily adjustable head switch point? - UK Vintage Radio Repair and Restoration Discussion Forum

ben · 11th Dec 2020, 11:39 pm

Here's an odd one.
My first camcorder was a Panasonic RX1, VHS-C. It worked okay but the head switching point was misadjusted, as evidenced by a bar about 1/8 way up the screen when those tapes were replayed on anything other than the camcorder. Note this was not a tape path problem, as you could partially track it out of the picture or 'move' it to some extent.

This was not a problem back then, as I used to dub the tapes from the camcorder and you could see little if any interference. I never felt comfortable enough to open it up to investigate it!

Now, however, the camcorder's mechanism doesn't work properly so I have to play those VHS-C tapes on a VHS cassette adaptor on another VHS deck if I want to view/digitize them. Which means I get noise.

So, I was wondering if anyone particularly recalls if there were any machines with an easily adjustable/acccessible head sw. point pot, so I can 'tune' the deck to the tapes. I imagine later built models would do this with a service menu. It's been years since I made that adjustment on a video, and have racked my brains trying to think of the board layouts but can't pin one down.

I have a large stack of possible candidates for twiddling, including:

1980s
Amstrad VCR 6000
Panasonic NV-G10, NV-G12, NV-G21, NV-D40, NV-250, NV-850.
PHILCO PH-883V (JVC HR-D110 clone Ferg. 3v35?)
Telefunken vr3940c (FERGUSON FV31R clone)
TOSHIBA V-66 (JVC HR-D140 Clone)
SHARP VC-481
Fisher FVH-P720

1990s
Samsung SX1260
Sony SLV-252
Philips vr 262
Goldstar T201
Samsung SV60

If al else fails I will just open them up one by one until I find one that's easy to adjust. My gut instinct suggests the Panny NV-G10 might be a good 'un for this experiment!

Graham G3ZVT · 12th Dec 2020, 12:06 am

If I've remembered my helical scan theory correctly...
How high up the head crossover occurs whilst recording is set by the "record timing pot" which basically sets the angular position of the drum when the frame sync occurs so, as I see it, the error will be burnt in to the recording thereafter

The actual switching point adjustment is a playback affair I don't really understand how the original camcorder moved the disturbance caused by incorrect record timing.

When you do the digital transfer you could zoom the image to 16:9 and crop the bottom edge. Sacrilege, but good enough for BBC/ITV et al

emeritus · 12th Dec 2020, 2:38 am

AFAIR the instructions for my VHS-C indicated that recordings made on the long play speed should only be played back usng the camera they were recorded on. I only used to record using standard play and had no problems playing back in an ordinary VHS using an adaptor so I don't know whether there was in fact a problem with long play recordings.

ben · 12th Dec 2020, 10:08 am

The recordings are all SP. The camcorder does not have LP.

Maarten · 12th Dec 2020, 8:52 pm

I'd try any of the 1980's recorders. I'd first go for the Panasonic as well.

dj_fivos_sak · 14th Dec 2020, 11:15 am

Hi. Most of my old Panasonic machines (NV-7500, NV-380 etc) have an adjustment on the servo board marked "PG shifter". This adjusts the postition of the head switching point. Some machines have seperate adjustments for head A and head B. Head switching should normally occur 6 or 7 horizontal lines before the vertical sync pulse.

Fivos

ben · 14th Dec 2020, 11:24 am

Thanks for the responses. I will get back to you once I've started my quest !

ben · 14th Dec 2020, 12:40 pm

First up a Thomson v510/JVC HRD140. A few pots but nothing clearly labelled and I don't know if I have the SM. May lift the pcb to double check.

dj_fivos_sak · 15th Dec 2020, 1:39 am

Hi. Here is a screenshot from the HR-D150 manual. It's not the exact same model but the procedure should be the same.

Fivos

dj_fivos_sak · 15th Dec 2020, 1:45 am

In case the screenshot is unreadable, R429 adjusts the PG (pulse generator/sw position) of head A and R427 adjust the PG of head B.

ben · 15th Dec 2020, 10:14 am

Thanks Fivos. Will take a look, but I have since discovered this is actually an HR-D170 not an HR-D140. I do have that manual somewhere.

dj_fivos_sak · 15th Dec 2020, 2:47 pm

OK. R443 is the variable resistor that alters the switching point on the HR-D170, according to the service manual.

Fivos

ben · 15th Dec 2020, 3:42 pm

Thanks Fivos. After I have sorted out the loading belt (details in this thread) I will try it.

11th Dec 2020, 11:39 pm	#1
ben Dekatron Join Date: Aug 2006 Location: Madrid, Spain / Wirral, UK Posts: 7,498	VHS VCRs with easily adjustable head switch point? Here's an odd one. My first camcorder was a Panasonic RX1, VHS-C. It worked okay but the head switching point was misadjusted, as evidenced by a bar about 1/8 way up the screen when those tapes were replayed on anything other than the camcorder. Note this was not a tape path problem, as you could partially track it out of the picture or 'move' it to some extent. This was not a problem back then, as I used to dub the tapes from the camcorder and you could see little if any interference. I never felt comfortable enough to open it up to investigate it! Now, however, the camcorder's mechanism doesn't work properly so I have to play those VHS-C tapes on a VHS cassette adaptor on another VHS deck if I want to view/digitize them. Which means I get noise. So, I was wondering if anyone particularly recalls if there were any machines with an easily adjustable/acccessible head sw. point pot, so I can 'tune' the deck to the tapes. I imagine later built models would do this with a service menu. It's been years since I made that adjustment on a video, and have racked my brains trying to think of the board layouts but can't pin one down. I have a large stack of possible candidates for twiddling, including: 1980s Amstrad VCR 6000 Panasonic NV-G10, NV-G12, NV-G21, NV-D40, NV-250, NV-850. PHILCO PH-883V (JVC HR-D110 clone Ferg. 3v35?) Telefunken vr3940c (FERGUSON FV31R clone) TOSHIBA V-66 (JVC HR-D140 Clone) SHARP VC-481 Fisher FVH-P720 1990s Samsung SX1260 Sony SLV-252 Philips vr 262 Goldstar T201 Samsung SV60 If al else fails I will just open them up one by one until I find one that's easy to adjust. My gut instinct suggests the Panny NV-G10 might be a good 'un for this experiment! __________________ Regards, Ben.

12th Dec 2020, 12:06 am	#2
Graham G3ZVT Dekatron Join Date: May 2010 Location: Greater Manchester, UK. Posts: 18,725	Re: VHS VCRs with easily adjustable head switch point? If I've remembered my helical scan theory correctly... How high up the head crossover occurs whilst recording is set by the "record timing pot" which basically sets the angular position of the drum when the frame sync occurs so, as I see it, the error will be burnt in to the recording thereafter The actual switching point adjustment is a playback affair I don't really understand how the original camcorder moved the disturbance caused by incorrect record timing. When you do the digital transfer you could zoom the image to 16:9 and crop the bottom edge. Sacrilege, but good enough for BBC/ITV et al __________________ -- Graham. G3ZVT

12th Dec 2020, 2:38 am	#3
emeritus Dekatron Join Date: Jan 2012 Location: Brentwood, Essex, UK. Posts: 5,349	Re: VHS VCRs with easily adjustable head switch point? AFAIR the instructions for my VHS-C indicated that recordings made on the long play speed should only be played back usng the camera they were recorded on. I only used to record using standard play and had no problems playing back in an ordinary VHS using an adaptor so I don't know whether there was in fact a problem with long play recordings.

12th Dec 2020, 10:08 am	#4
ben Dekatron Join Date: Aug 2006 Location: Madrid, Spain / Wirral, UK Posts: 7,498	Re: VHS VCRs with easily adjustable head switch point? The recordings are all SP. The camcorder does not have LP. __________________ Regards, Ben.

12th Dec 2020, 8:52 pm	#5
Maarten Dekatron Join Date: Dec 2007 Location: Haarlem, Netherlands Posts: 4,203	Re: VHS VCRs with easily adjustable head switch point? I'd try any of the 1980's recorders. I'd first go for the Panasonic as well.

14th Dec 2020, 11:15 am	#6
dj_fivos_sak Heptode Join Date: Mar 2015 Location: Lefkada, Greece Posts: 969	Re: VHS VCRs with easily adjustable head switch point? Hi. Most of my old Panasonic machines (NV-7500, NV-380 etc) have an adjustment on the servo board marked "PG shifter". This adjusts the postition of the head switching point. Some machines have seperate adjustments for head A and head B. Head switching should normally occur 6 or 7 horizontal lines before the vertical sync pulse. Fivos

14th Dec 2020, 11:24 am	#7
ben Dekatron Join Date: Aug 2006 Location: Madrid, Spain / Wirral, UK Posts: 7,498	Re: VHS VCRs with easily adjustable head switch point? Thanks for the responses. I will get back to you once I've started my quest ! __________________ Regards, Ben.

14th Dec 2020, 12:40 pm	#8
ben Dekatron Join Date: Aug 2006 Location: Madrid, Spain / Wirral, UK Posts: 7,498	Re: VHS VCRs with easily adjustable head switch point? First up a Thomson v510/JVC HRD140. A few pots but nothing clearly labelled and I don't know if I have the SM. May lift the pcb to double check. Attached Thumbnails __________________ Regards, Ben.

15th Dec 2020, 1:39 am	#9
dj_fivos_sak Heptode Join Date: Mar 2015 Location: Lefkada, Greece Posts: 969	Re: VHS VCRs with easily adjustable head switch point? Hi. Here is a screenshot from the HR-D150 manual. It's not the exact same model but the procedure should be the same. Fivos Attached Thumbnails

15th Dec 2020, 1:45 am	#10
dj_fivos_sak Heptode Join Date: Mar 2015 Location: Lefkada, Greece Posts: 969	Re: VHS VCRs with easily adjustable head switch point? In case the screenshot is unreadable, R429 adjusts the PG (pulse generator/sw position) of head A and R427 adjust the PG of head B.

15th Dec 2020, 10:14 am	#11
ben Dekatron Join Date: Aug 2006 Location: Madrid, Spain / Wirral, UK Posts: 7,498	Re: VHS VCRs with easily adjustable head switch point? Thanks Fivos. Will take a look, but I have since discovered this is actually an HR-D170 not an HR-D140. I do have that manual somewhere. __________________ Regards, Ben.

15th Dec 2020, 2:47 pm	#12
dj_fivos_sak Heptode Join Date: Mar 2015 Location: Lefkada, Greece Posts: 969	Re: VHS VCRs with easily adjustable head switch point? OK. R443 is the variable resistor that alters the switching point on the HR-D170, according to the service manual. Fivos

15th Dec 2020, 3:42 pm	#13
ben Dekatron Join Date: Aug 2006 Location: Madrid, Spain / Wirral, UK Posts: 7,498	Re: VHS VCRs with easily adjustable head switch point? Thanks Fivos. After I have sorted out the loading belt (details in this thread) I will try it. __________________ Regards, Ben.