Share:
Notifications
Clear all

Fisher vbs-7000/ Sanyo Vtc-9100 Betamax  

 
acj1980
(@acj1980)
Active V-Ratter Registered

God evening.

I have an old betamax vcr from Sanyo/Fisher , its the same giant machine, a very heavy tank :-), i have some issue in the picture, i hope you can spot the red horizontal stribes in the picture, does anyone know what that is? it´s only when i play a movie, i have seen this phenomenon before on other formats like older vhs

Stribes

 I hope someone know what that issue is and how i can fix it,

regards

Alex

ReplyQuote
Topic starter Posted : 26/08/2020 11:30 pm
irob2345
(@irob2345)
Active V-Ratter Registered

Do you have any LW or MW broadcasting transmitters nearby?

ReplyQuote
Posted : 27/08/2020 12:09 am
Doz
 Doz
(@doz)
Noble V-Ratter Registered

@acj1980 Is this direct video out or via the modulator?

ReplyQuote
Posted : 27/08/2020 8:02 am
acj1980
(@acj1980)
Active V-Ratter Registered

@irob2345

No, and im confident that it isn´t that issue, i think it could be a croma error

ReplyQuote
Topic starter Posted : 27/08/2020 10:44 am
acj1980
(@acj1980)
Active V-Ratter Registered

@doz

It´s via the RF, but the same picture if i used direct video connection

ReplyQuote
Topic starter Posted : 27/08/2020 10:45 am
irob2345
(@irob2345)
Active V-Ratter Registered

The chroma as picked up by the heads is in-band for MW radio. Used to be a common problem in Sydney around the Parramatta River basin.

Also, I seem to recall there is an adjustment that nulls the track-to-track crosstalk which mainly affects the down-converted chroma.

ReplyQuote
Posted : 27/08/2020 11:29 am
acj1980 liked
Doz
 Doz
(@doz)
Noble V-Ratter Registered

@acj1980

OK, that's me out! I seem to remember there being a modification (at least in the UK) , to the little modulator can behind the door at the top rear to stop this sort of thing... adding a 1uF cap if memory serves... but it was a long time ago...

ReplyQuote
Posted : 27/08/2020 12:14 pm
Horris and acj1980 liked
Katie Bush
(@katie-bush)
Famed V-Ratter Moderator

I remember seeing something very similar in a few Sharp branded machines from the late '80s. There was an excessive amount of gain somewhere in the video amplification path, on playback. In those machines, there were a couple of trimmer pots that could be adjusted. It reduced the video gain, and thus, the saturation on screen. It had the desired effect of removing 'Hanover bar' type of effect. The adjustment wasn't too critical, but critical enough, and there was always the temptation to ramp up the gain as far as possible before the effect became visible. The trouble was, not all recordings were recorded equally, so some played just fine, whilst others would show the effect.

The aim was to get the saturation 'off tape' to look something equal to that 'off-air'. It needed a few different recordings, a little time, and some patience - or alternatively, some expensive kit to set those levels as per factory.

ReplyQuote
Posted : 27/08/2020 6:16 pm
acj1980 liked
irob2345
(@irob2345)
Active V-Ratter Registered

The thing to remember is these machines used offset azimuth on the heads so that the track laid down by one head became the guard band for the other, thus allowing the crazy slow tape speeds and long recording times.

This works very well for the FM luminance signal but not so well for the down-converted chroma, which was recorded "AM" using the luminance signal as AC bias. Because it was lower in frequency, some of the A head signal would be picked up by the B head and vice versa.

VHS and Beta both use a nifty cancellation circuit to solve this issue. Yours might be broken or out of adjustment.

Philips VCRs used a larger azimuth offset and eschewed the chroma cancellation circuit.

Another thing that can cause a similar effect (more like ghost patches of colour) is if the tape has been erased and re-recorded. Complete erasure of the previous chroma signal sometimes doesn't happen. No problem with the luma, the capture effect of FM takes care of that.

I once had a Sony VHS VCR (always sounds like an oxymoron to me!) that would intermittently lose capstan servo lock on playback. Problem turned out to be remnant servo sync pulses (what do they call that track again??) from previous recordings. Lowering the gain in the servo head amp fixed this one.

ReplyQuote
Posted : 28/08/2020 6:00 am