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  #1  
Old 08-12-2017, 01:56 AM
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Sony Karaoke VCR Dim VFD

I was given a Sony SLV-KH3(ME) karaoke VCR which is basically a multi-region VCR with a few extra features so you can use it for karaoke. I particularly like the pitch bender and surround effects. Makes some movie scenes absolutely hilarious.

At first though I thought the VFD was dead but when I turned the lights off it's actually there, just really, really dim from presumably running for thousands of hours. Understanding it is likely weak with age is there any way to brighten it even a little?
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Old 08-12-2017, 06:07 AM
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While I've not worked on that model of Sony, some later Sony VCRs had a 1uF cap on the VFD display driver board that would open, causing no display. The 1uF cap was a low-ESR type, available only from Sony. The "fix" was to use a common 3.3uF cap of the same voltage (IIRC, 160V or so...) to get the same low-ESR effect.

The cap was the filter for the switching "boost" converter supply for the VFD. The output of the supply was AC in the 30-80KHz range.

Some VFD's use a variable duty cycle to vary the display brightness - you may have one similar - you'd have to scope the filaments to see if you have a small duty cycle (narroww pulses) - the microprocessor typically controlled that. In operation (tape playing/REW/FF/loading), the display is brighter, and when idle, the display is dimmer - all done by varying the duty cycle of the filaments.

EDit: The third possibility is that, yes, your VFD is tired/worn out. I've seen this in car clocks, and digital scales used by trucking firms.

Most of those Karaoke VCRs went for 600 bucks or more in the 90s.
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Old 08-14-2017, 01:43 AM
centralradio centralradio is offline
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My Sharp VCR has a dim display on it since I picked it up at the fleamarket years ago.I got to check it out.I remember at the shop years ago when RCA/GE send out a supplement to put into the service manuals and had a kit to fix their VCRs with dim displays.

BTW thanks for the tip Brian.
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Old 08-14-2017, 09:37 AM
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Quote:
Originally Posted by centralradio View Post
I remember at the shop years ago when RCA/GE send out a supplement to put into the service manuals and had a kit to fix their VCRs with dim displays.
That could cover a LOT of models! There were the Hitachi-made VCRs with either discrete components in the DC-DC converter circuit, or had the DC-DC conv. module, either would fail from bad caps. Then there were the Samsung-made RCA-GE units with capacitors failing in the power supply. Thompson issued a rebuild kit for those. The driver transistor would often fail in those too. I would take that out and check the gain of the transistor since it wouldn't actually go open or short and read fairly normal with simple testing with a meter, and replace it as needed.
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Old 08-14-2017, 01:01 PM
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Quote:
Originally Posted by Ed in Tx View Post
That could cover a LOT of models! There were the Hitachi-made VCRs with either discrete components in the DC-DC converter circuit, or had the DC-DC conv. module, either would fail from bad caps. Then there were the Samsung-made RCA-GE units with capacitors failing in the power supply. Thompson issued a rebuild kit for those. The driver transistor would often fail in those too. I would take that out and check the gain of the transistor since it wouldn't actually go open or short and read fairly normal with simple testing with a meter, and replace it as needed.
Thanks Ed for the details.It was awhile back and could not remember all the info .On the Sony VCRs I had several issues when those transistor look alike circuit protectors blown out. At first It took me on the loop troubleshooting it until I read up on it and found out what they were..The Sony SLV-KH3 is will worth it to fix it.
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Old 08-14-2017, 02:22 PM
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Quote:
Originally Posted by Ed in Tx View Post
That could cover a LOT of models! There were the Hitachi-made VCRs with either discrete components in the DC-DC converter circuit, or had the DC-DC conv. module, either would fail from bad caps. Then there were the Samsung-made RCA-GE units with capacitors failing in the power supply. Thompson issued a rebuild kit for those. The driver transistor would often fail in those too. I would take that out and check the gain of the transistor since it wouldn't actually go open or short and read fairly normal with simple testing with a meter, and replace it as needed.
For the Hitachis, they made two kits - one early and one later - here's the later.

For the Samsungs, there were so many Goldenrods about them, they made a booklet identifying the changes that were to be made. Rectifiers, caps, spacer on a gear, and a check of the mode switch type. I have the booklet here somewhere, a freebie from RCA that came with our service lit subscription. All of the goldenrods I have are on microfiche, so not easily transcribed. Last time I printed from a microfiche, the ODU library was getting 70 cents a page...

The later VCRs with the VEPSXXXXX power supply modules, we got the kits from MAT or RCA, save for warranty work, where RCA made us swap supplies. The duds went back to RCA, so we had some fun and marked them with a small knife. After rebuild in Mexico, they were issued as new stock - proof that even RCA passed used goods off as new stuff. No reconditioned stickers like the modules and tuners - just a sealed bag with a rebuilt power supply. They paid 0.7 hours labor to replace the supply and more than that for "processing" the claim. Good money for an easy fix. Lightning killed them all - but RCA honored the warranty.
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Old 08-14-2017, 02:27 PM
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OP/MIPS, I checked my Sony ESI library CDs (23 of them...) and haven't found a service manual. Odd unit, or too new for my stuff, which ended in 2005. A google search turned up the usual manual sellers, none of which showed a front page of the manual - handy to search with, as the Sony part number (9XXXXXXX number) is usually on the front page.
Union Electronics or Encompass might still have one if you need a manual, but they charge $$$$ for most Sony manuals.
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Old 08-14-2017, 07:09 PM
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I am in the process of saving my pennies right now for the service manual for an unrelated Pioneer LC-V300.
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