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Old 18th May 2021, 11:01 am   #1
Paul Stenning
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Default Mitsubishi HS-B52 VHS VCR playing slowly

I have just received a Mitsubishi HS-B52 VHS VCR (which was offered as untested due to no tapes) that has a weird problem.

When playing pre-recorded tapes (which are SP speed) they are played too slowly. It seems that the VCR thinks SP tapes are LP. I cannot see anything on the remote or the multitude of front panel controls to set playback speed, and indeed it shouldn't be necessary.

Does anyone have any ideas what could cause this and how I can resolve it, or even fix it to always work in SP regardless please?

I don't have a service manual (or even a user manual, although I have just ordered a copy of that).

Thank you!
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Old 18th May 2021, 11:35 am   #2
toshiba tony
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Default Re: Mitsubishi HS-B52 VHS VCR playing slowly

I'd be looking for CTL pulses on the control head, didn't these revert to LP in the event of the pulses being absent? What is the clock display showing on playback?
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Old 18th May 2021, 11:36 am   #3
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Default Re: Mitsubishi HS-B52 VHS VCR playing slowly

The first thing I'd do is to get hold of a genuine LP tape and see if that plays correctly with good servo lock. If it does then you have a very odd speed switching fault - the LP sign would then be on the display. If it doesn't then I'd be looking at the capstan motor - is it free and is the driven clutch not slowing it down?

Crossed with Tony - do check the ACE head is clean and in visual alignment. You never know who's been here before you!
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Old 18th May 2021, 11:44 am   #4
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Default Re: Mitsubishi HS-B52 VHS VCR playing slowly

I don't have an oscilloscope so can't check for pulses. The time on the display doesn't change when playing, which I guess points to the pulses being missing. Neither SP or LP are lit when playing (although SP is lit when not playing).

Sounds like the first place to look is the control/audio head, make sure it's clean and has no dry joints, and that the tape appears to be passing over it and the adjacent guides smoothly.

The tapes I tried have hi-fi sound so the audio on the control/audio head wouldn't be used. I do have a couple with only linear mono sound which will be interesting to check.

I don't have any LP tapes; the only tapes I have are pre-recorded SP ones. Although I could probably record something on an unwanted tape in LP between two other VCRs.

Quote:
Originally Posted by Welsh Anorak View Post
You never know who's been here before you!
This is very true. Apparently the main belt and pinch roller were replaced a few years ago and the old ones were included with the unit. The lid screws are rather loose too, and the eject button had fallen inside.
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Old 18th May 2021, 11:57 am   #5
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Default Re: Mitsubishi HS-B52 VHS VCR playing slowly

I think you're on the right track (no pun intended). A good polish might be all that's needed.
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Old 18th May 2021, 1:48 pm   #6
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Default Re: Mitsubishi HS-B52 VHS VCR playing slowly

Progress! The head appeared to be correctly aligned (as far as I can see by eye) and cleaning had no effect. However unplugging and replugging the cable to the top of the audio/control head PCB has got it playing at the correct speed.

So must have been a dodgy connection. I am reluctant to use any contact cleaner there though in case it finds its way into the tape path. Gently moving the cable while it's playing doesn't have any effect so it seems to be connected OK now.

The next issues are:

1. The left audio channel level indicator on the display is scarcely moving while the right channel indicating is peaking at the first red box (can't see the number as the display is rather dim). However the sound from speakers is equal level (by ear) on both channels. That's not really an issue.

2. The picture is a bit dark and over-saturated, as though the chroma is OK but the luminance is low. The TV is also having occasional problems syncing to it, either random pulling left or right in the top half, or losing sync completely. The hi-fi sound continues cleanly throughout. This TV works fine with Philips VR-840 VCRs. Unfortunately without a 'scope I can't view the composite video signal.

I suspect there are more iffy plug connections and maybe also iffy presets. Maybe some unplugging and replugging, and adjusting presets back and forth and returning to original position could help?

I don't suppose anyone has a service manual for this unit?
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Old 18th May 2021, 1:56 pm   #7
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Default Re: Mitsubishi HS-B52 VHS VCR playing slowly

Thought I might be on the right theme, there were other machines that went to LP by default. Well done.
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Old 18th May 2021, 3:29 pm   #8
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Default Re: Mitsubishi HS-B52 VHS VCR playing slowly

I have dismantled it further and am now looking suspiciously at a 1000uF 6.3V capacitor in what appears to be the video output buffer to the SCART socket on the "SIGNAL" board. There is what appears to be some yellow discharge on one of its legs. If it is the signal coupling to the SCART and is unwell (high ESR) it could explain the problem.

A couple of presets on the PCB in that area seem to have a momentary effect on the saturation before it returns to the usual dull. They are now returned to the original positions until I have replaced that capacitor and a couple of others in the same area.

No progress with the audio level indicators yet, but with the number of cables going from the "HIFI/NICAM" board to the front panel, I'm wondering if there is an IC on the front panel PCB for the level indicators.

It will probably be tomorrow evening before I do much more with it.
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Old 18th May 2021, 5:57 pm   #9
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Default Re: Mitsubishi HS-B52 VHS VCR playing slowly

Pull the PSU and give it the once-over. I've had nineties Mitsubishi's before where power supply secondaries have leaked creating quite the mess! Almost to the point of looking like a spillage/ liquid damage has occurred. The smell is, of course, a dead (fish) giveaway! A real kipper of commiseration!

A dim display can often be a tell-tale indicator of poor PSU health. The VFD, naturally, being the window to the VCR's soul!
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Old 14th Jun 2021, 7:31 pm   #10
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Default Re: Mitsubishi HS-B52 VHS VCR playing slowly

I have now given up trying to repair this and am offering it free here https://www.vintage-radio.net/forum/...d.php?t=181106
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