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Old 12th Jan 2021, 12:37 pm   #1
P-Sussex
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Default Sanyo vtc9300 no audio on recording

I have obtained a Sanyo vtc9300 VCR, it was a spares or repairs. The idea is to restore it back to working condition, just as a fun learning project during the lockdown period.

Bit by bit I have gradually brought the machine back to life from near dead. Playback is now good and having adjusted the VR204 on the main board and replaced some of the e. capacitors around the area.

The main problem is with recording, which is via direct video/audio in. Both audio and video can be monitored during recording, so it is passing through OK. On playback no audio has been recorded, the previous sound recording is still present. I notice the video has some odd colour flashes that move around on the video. Slightly different to the rainbow loss of colour effect related to the VR204 adjustment. I found a reference elsewhere regarding a Sony machine having this problem and it was suggested that the erase head may be at fault or the bias oscillator may be at fault.

I'm simply a home tinker with school boy electronics experience so I do have a lot to learn. I was wondering if anyone else here has had a similar issue with this machine and any areas on the boards I should look at? I have the service manual as a reference.

Many thanks for reading.
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Old 12th Jan 2021, 1:14 pm   #2
G6ONEDave
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Default Re: Sanyo vtc9300 no audio on recording

The erase head is part of the fixed head assy, which also contains the audio head and control track head. It is located to the left of the drum assy, at least that's how it appears in the parts diagram. Check for broken wires at the head, then S604 at pcb (W2) video and audio circuit. After that check the bias oscillator circuit T601, Q606 (2SD438F) for actual oscillation. If T601 is OK, it could be a lazy transistor. Ideally you would check waveforms with an oscilloscope. The bias oscillator is on the bottom left of the W2 diagram. Also check that there is a supply voltage getting to the oscillator circuit.
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Old 12th Jan 2021, 7:21 pm   #3
P-Sussex
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Default Re: Sanyo vtc9300 no audio on recording

Thank you for the very helpful reply Dave.

I traced the audio erase block (ACE unit) back to the suggested points and all seems fine. The connections on both erase heads (I did not realise they are chained off each other) seemed OK too. I still need to understand how to test the the bias oscillator circuit T60, however on reassembly the sound was recording. Although I have not really done anything perhaps this is a temp fix due to dry joint? I notice this part seems very hard to obtain?

I don't have an oscilloscope as yet for such involved testing, however with the nature of my interest in old VCRs it seems it might be a good investment, and perhaps a steep learning curve. I would not have access to the numerous test tapes signal generators required that many service manual mention. Can you get by with just the oscilloscope?

Now that I can record the sound, I notice there is a noticeable buzz on the soundtrack. This buzz is present when the machine is on with no signal running through it. If I play a pre recored tape the buzz goes and is not present. But my own recording catch this buzz. Could this be a capacitor PSU issue? Should I be checking these?

Thank you again for helping me with what I hope to be a very satisfying and rewarding hobby.
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Old 13th Jan 2021, 12:17 am   #4
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Default Re: Sanyo vtc9300 no audio on recording

On the bottom panel there are 2 plastic type switches, if they are like a old VHS Panasonic VCR I was restoring the contacts get tarnished. I switched off and sprayed them with contact/switch cleaner and waited for it to dry and powered up and made another recording this was played back and the problem had gone. It's worth trying on your Sanyo I can't comment further as I no longer have the service manual. The way I found out about problems with the bias oscillator was when recording I was left with sound from the previous recordings. Is yours doing this then this could be what's wrong.

Regards, David.
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Old 13th Jan 2021, 10:36 am   #5
P-Sussex
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Default Re: Sanyo vtc9300 no audio on recording

Thank you for that advise. Currently it is recording sound after disconnecting and examining the ACE unit, albeit with a buzz on the soundtrack on new recordings. I suspect this may be simply down to luck of disconnection and reconnection that it now records. Yes the previous sound was not being erased. Do you think contact cleaner could help with the buzz I'm now getting or more of a capacitor issue maybe in the PSU?
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Old 13th Jan 2021, 11:00 am   #6
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Default Re: Sanyo vtc9300 no audio on recording

I wouldn't suspect capacitors yet, especially as the ones on these machines are pretty reliable. More likely are the connections as you've discovered, so check the pins' soldering and also clean the connectors by removing and re-inserting them several times, possibly with a small wipe of cleaner over the pins.
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Old 13th Jan 2021, 12:37 pm   #7
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Default Re: Sanyo vtc9300 no audio on recording

When checking the connector pins for bad solder joints, also check the actual heads to make sure that their pins are soldered properly to the mini pcb that the wires join to. The head pins can also become 'dry jointed'. Given that the audio record seems to be OK now but you have a new buzz, it could be a dodgy screening connector at one of the plug/socket termination points.

If the erase bias signal completely goes, you will still get a recorded vision signal but it will contain a lot of coloured noise on the playback image. The recorded audio will either be non existant or mixed with the original audio.

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Old 13th Jan 2021, 7:18 pm   #8
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Default Re: Sanyo vtc9300 no audio on recording

I am probably mentioning the obvious, but have you given the Audio erase head a really good clean, only I assume its Betamax and you did get some illogical symptoms at times, with Betamax.
Ken G6HZG.
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Old 14th Jan 2021, 10:00 am   #9
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Default Re: Sanyo vtc9300 no audio on recording

I used to get this sort of problem often on vcr’s of many makes, my solution was always to remove the plug/ socket and solder the wires directly. Th decks seldom came back in.
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Old 14th Jan 2021, 6:53 pm   #10
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Default Re: Sanyo vtc9300 no audio on recording

Thank you so much everyone for your very helpful comments. I'll have another go at it armed with all the info supplied.
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Old 16th Jan 2021, 1:37 am   #11
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Default Re: Sanyo vtc9300 no audio on recording

Hi. On the W1 board (servo, head pre-amp, located at the left-hand side of machine) there are two rec/play switches, and there's another rec/play switch on the W2 board (luminance, chroma, audio, located at the bottom side of machine) in the audio circuit. Clean the contacts of the switches with a contact cleaner like DeoxIT.
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Old 16th Jan 2021, 2:27 am   #12
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Default Re: Sanyo vtc9300 no audio on recording

Quote:
Originally Posted by G6ONEDave View Post
After that check the bias oscillator circuit T601, Q606 (2SD438F) for actual oscillation. If T601 is OK, it could be a lazy transistor.
Had a similar issue with a Philips machine some time ago, and it turned out to be a bad transistor. Definitely worth a check!
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