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Old 10th May 2022, 12:40 pm   #1
Michael Maurice
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Default Toshiba RD-XV47 DVD/VCR Combo.

I suppose this just about fall into the vintage section. If not it could be moved to MT.

This machine is driving me nuts.

It came in with the cassette not functioning, so I replaced the LED and opto transistor. I also dismantled and cleaned the mode switch.

It now switches on, you can load a tape and do everything except that after a few seconds it switches to standby.

It does this whether a tape is loaded or not, whether its playing, rew or ff or not and even if its switched to DVD or HDD.

Can someone enlighten me as to what may be causing this?
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Old 10th May 2022, 1:04 pm   #2
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Default Re: Toshiba RD-XV47 DVD/VCR Combo.

Michael - you have my sympathies. This is a horrible fault on a nasty chassis.

There's a diode in the power supply, 1N5397 (D1150 on later models) on the 5v line that can cause this.
There are also a multitude of diodes (1N4001s) on the main board that can cause this. Despite you having ruled the VHS deck out it still might be this at the root of the problem, especially as I assume this didn't happen before.
The LED is a special type and might be causing it to shut down, but of course the original isn't available any more.
As you know taking the deck out is a tricky business - especially that ribbon cable - but I know your workmanship so I doubt you've made an error here. The trouble with these, unlike the Panasonics, is that removing either deck will cause it to shut down anyway.
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Old 10th May 2022, 2:03 pm   #3
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Default Re: Toshiba RD-XV47 DVD/VCR Combo.

If I remember correctly this is a Samsung unit. I didn't stock these as I would have to repair them if I did...John.
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Old 10th May 2022, 3:17 pm   #4
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Default Re: Toshiba RD-XV47 DVD/VCR Combo.

No, it's a Funai. Very wise move on your part, though, John!
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Old 10th May 2022, 4:29 pm   #5
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Default Re: Toshiba RD-XV47 DVD/VCR Combo.

Say no more! J.
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Old 10th May 2022, 7:55 pm   #6
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Default Re: Toshiba RD-XV47 DVD/VCR Combo.

remember doing quite a few of the funai and toshiba ones of these and like glyn would change the in5397first [even if it checks o/k on the meter. ]
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Old 10th May 2022, 8:12 pm   #7
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Default Re: Toshiba RD-XV47 DVD/VCR Combo.

+1 for 'That Diode', and don't expect it to look bad on a meter test. I nearly missed it on the one example I had and was only brought back to it by Glyn and others.

When I took it and a couple of others out - there are more than one of those diodes in the unit - the only way I could get the 'bad' diode to look different was by passing about an Amp through it with a current limited bench supply and measuring the forward voltage drop across it while doing that. The drop was much greater across the diode taken from D1150 position than across any other examples of the same diode from other parts of the circuit, but on a simple meter 'diode test' it looked no different.
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Old 23rd May 2022, 5:26 pm   #8
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Default Re: Toshiba RD-XV47 DVD/VCR Combo.

An update:

I replaced all the large diodes in the power supply with UF5408’s. I thought it had cured it but after around 10 mins it went to standby.

Next I replaced the 1N400- diodes at the back of the video deck but the problem still exists.
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Old 23rd May 2022, 6:00 pm   #9
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Default Re: Toshiba RD-XV47 DVD/VCR Combo.

Specifically, which diodes did you replace (which component numbers?)

The ones which are used as the rectifiers on the low voltage side (SB340, SB390) are Schottky types with low forward voltage drop. The diode which often causes problems on the similar RDXV60 (D01150) is in series with the input to one of the regulators and what happens is that the forward voltage drop across the diode increases to the point where the input voltage to the regulator is too low for the regulator to be able to work properly, and that is what causes the weird behaviour attributed to failure of that diode.

Attached, a section from the specific diagram for the RDXV47 showing the equivalent diode (D1101) ringed, along with one (D1121) which the diagram says has been removed and replaced with a wire link - it might be as well to check that yours does have a wire link and not a diode. All of those 'SB....' diodes are likely suspects but they need to be replaced with equivalent low drop Schottky types.
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Old 23rd May 2022, 7:06 pm   #10
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Default Re: Toshiba RD-XV47 DVD/VCR Combo.

Is the UF5408 a suitable replacement?
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Old 23rd May 2022, 7:31 pm   #11
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Default Re: Toshiba RD-XV47 DVD/VCR Combo.

on all the one i did back in the day ,had to fit the exact type of diode .as i said before the in5937 was the biggest culprit on these .
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Old 23rd May 2022, 7:55 pm   #12
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Default Re: Toshiba RD-XV47 DVD/VCR Combo.

Quote:
Is the UF5408 a suitable replacement?
For the SBs, not quite because although the UF5408 is a fast recovery diode its forward voltage drop is stated to be a maximum of 1.3V here:-

https://uk.rs-online.com/web/p/schot...ifiers/9033318

Information about ie. SB340 here, which states a maximum forward voltage drop of 0.5V.

https://uk.rs-online.com/web/p/schot...ifiers/8061996

That's quite a difference in the voltage drop - so much so that I wonder if the rather high voltage rated UF5408 is actually several lower voltage rated diodes in series inside one package. I would try putting the SB390s back where they came from and replace the SB340s, which are available from RS.

The SB390s seem a little bit harder to find which is why I am suggesting a staged approach - if replacing the SB340s with like for like works, great, you don't have to trawl the internet for SB390s. The SB390s are shown as in stock at the likes of Mouser and Digikey.

The fact that changing the diodes made such a big difference to the nature of the fault (delayed the onset of the fault by quite a bit) makes me think you are very close to the finish line now. I think you may just need to fit the correct diode types, and it should be a relatively cheap thing to try.
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Old 23rd May 2022, 8:58 pm   #13
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Default Re: Toshiba RD-XV47 DVD/VCR Combo.

I don't have the original diodes, what I'll do is order some SB340's and SB3100 (40V and 100V PIV) and use the 3100 in place of the 390's. Lets see what happens.

Also, I used 1N5399 instead of the 1N4006. I will replace with 1N4006's or 4007's.
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Old 24th May 2022, 11:41 am   #14
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Default Re: Toshiba RD-XV47 DVD/VCR Combo.

Quote:
Originally Posted by Michael Maurice View Post
Is the UF5408 a suitable replacement?
Only for normal fast rectifiers, not for Schottky types.
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Old 24th May 2022, 6:17 pm   #15
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Default Re: Toshiba RD-XV47 DVD/VCR Combo.

I confess when I looked at this link (as given above)

https://uk.rs-online.com/web/p/schot...ifiers/9033318

I was surprised to see the UF5408 listed under 'Schottky Diodes....' as I didn't think it was, whereas the SB series definitely are Schottky. Only when I looked again did I see that the UF5408 is listed under 'Schottky Diodes and Rectifiers, but that is good, as it reinforces the idea that the diodes really need to be the correct (Schottky) type.
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Old 26th May 2022, 8:00 am   #16
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Default Re: Toshiba RD-XV47 DVD/VCR Combo.

I've changed the diodes for those specified in the service manual. It now comes on, stays on for 10 seconds, the display shows 'POWER OFF' then it shuts down.
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Old 26th May 2022, 7:39 pm   #17
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Default Re: Toshiba RD-XV47 DVD/VCR Combo.

ooops, the most likely culprit is d1150 [in5397 ][ not in5937 my typo] did quite a few of these back in the day . dont bother testing it with a meter just change it. we used to fit the exact one in5397 is 600v piv and 1.5a as far as i remember that was the only problem we had with them. regards brian at least these did,nt have the dvd ram problems like all the panasonics we did of the day ez47/48/49
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Old 26th May 2022, 11:43 pm   #18
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Default Re: Toshiba RD-XV47 DVD/VCR Combo.

There is no D1150 on this model and I've changed all the others using the parts specified in the manual.
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Old 9th Jun 2022, 6:14 pm   #19
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Default Re: Toshiba RD-XV47 DVD/VCR Combo.

Quote:
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I've changed the diodes for those specified in the service manual. It now comes on, stays on for 10 seconds, the display shows 'POWER OFF' then it shuts down.
I’m no further forward with this. all the large diodes in the PSU secondary have been changed.

All the 1N diodes on the VCR board have been replaced.

The mode switch has been cleaned, the photo transistor and LED under the deck has been replaced. Where do I go from here?
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Old 9th Jun 2022, 6:28 pm   #20
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Default Re: Toshiba RD-XV47 DVD/VCR Combo.

Secondary psu caps ?
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