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Thread: Fostex G24S Meter Problem

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    Fostex G24S Meter Problem

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    I figured that I'd post this question here as I know that there have been some good G24 threads on here in the past.

    I have a slightly sick G24 which I'm sure was working better when I last tried it a few months ago. Some of the issues are down to the notorious capacitors on the audio cards and, while I'm not usually a fan of wholesale recapping, I've just taken delivery of 600 replacement capacitors so I'll be busy with the soldering iron over the next few weeks.

    However, I was wondering whether anyone might have come across another issue that I'm seeing? The meters flicker rapidly whenever there are more than about 3 LED's alight on a channel - and sometimes just when a single LED is alight on some channels. The power on sequence shows that all LED's are working and the rest of the control panel seems fine so I think the problem must lie at the other end in the main machine. For those that don't know the G24, as far as I can work out, the analogue meter signals go into a multiplexer where 4 channels are multiplexed into one which is fed to an ADC so that only digital information is sent to the control panel.

    So I thought I'd ask whether anyone has seen this flickering meter behaviour and managed to fix it?
    JRP Music - Audio Mastering and Restoration
    http://www.jrpmusic.co.uk

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    Not sure the exact cause of flicker meters...but your audio card issues (and maybe the meters too) are most likely due to the Dolby S chips...and no recapping will fix that...you would need to replace the Dolby S chips, which have been out of production for a long time.
    Pretty much everyone with a Fostex Dolby S machine that's had issues, it was due to the chips going bad, and those decks were done...not repairable, AFAIK.

    I had a G16, but it was the earlier Dolby C...and they never had problems...and no, you can't swap C chips into the machines designed for S.

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    Quote Originally Posted by miroslav View Post
    ...but your audio card issues (and maybe the meters too) are most likely due to the Dolby S chips...and no recapping will fix that...you would need to replace the Dolby S chips, which have been out of production for a long time.
    Thanks for the reply. I've been working with the Dolby bypassed (and the service manual shows that the Dolby modules are not in the signal path when bypassed) so they're not an issue. On the working channels the audio is fine when the meters are flickering (and the meter levels look sensible if they weren't flickering). Dolby S isn't really needed at the moment as most of the tapes that I'm likely to be playing are old 8 tracks which would use Dolby A if they used any noise reduction at all. I'll start with the capacitors that are obviously leaking - the ones with little blobs of brown stuff coming out and keep going. Does the G16 use surface mount components?
    JRP Music - Audio Mastering and Restoration
    http://www.jrpmusic.co.uk

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    OK...you're talking about playback of older tapes not needing the Dolby S engaged...but then you say "8 tracks"...?
    How are you playing old 8 track tapes on a G24S 24-track machine that used 1" tape?
    What tape format are the 8 track tapes...?

    Sorry...it's just not making any sense, and I don't know how that would even work and provide good playback, regardless of the Dolby S issue...thought I may be misunderstanding your post altogether.

    Oh...I no longer have the G16...but it was pretty much the same basic design as the G24...just 1/2" 16 tracks, and mine was the initial Dolby C version...I think the S version came out pretty soon afterward, like maybe 2 years later, along with the G24S.

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    It sounds like he has some 1" 8-track masters from the 60s or 70s and is using the G24 to digitise them. I have done this with the MSR24 and it does work, though the quality is not likely to be as good as an actual 8-track head.

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    I know nothing of the G24 but from first principles...You either have a drive amplifier going instable and duff caps could certainly be the problem there or you have ripple on the supply lines which could be capacitors or a faulty regulator.

    My first diagnostic step would be to scope the supply rails. Don't have a scope? Oooo! You are going to struggle with annyloggy tape machines without one!

    Dave.

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    Quote Originally Posted by jpmorris View Post
    It sounds like he has some 1" 8-track masters from the 60s or 70s and is using the G24 to digitise them. I have done this with the MSR24 and it does work, though the quality is not likely to be as good as an actual 8-track head.
    I kinda thought it might be something like that...and considering that the 1" 8-track has wider track widths, the G24 would certainly pick them up on playback, though TBH, I would also think there would be some overlap....like every 3 tracks of the G24 would cover 1 track of the 1" 8-track...and even then, I doubt the the actual position would line up perfectly, and as you say, the quality is not likely to be as good....so I kinda wonder if it is worth it, I mean, to go to all the trouble of recapping the G24 just to get some playback from it, knowing that the Dolby S chips are critical for actually ever recording with the deck....?

    I guess if I had enough old 1" 8 track tapes that needed transfer...I would source a 1" 8 track deck that was closer in spec to the tapes.
    Maybe not an easy thing to find, but I just don't see much value in fixing the G24, knowing its S-chip issues.

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    Quote Originally Posted by miroslav View Post
    I kinda thought it might be something like that...and considering that the 1" 8-track has wider track widths, the G24 would certainly pick them up on playback, though TBH, I would also think there would be some overlap....like every 3 tracks of the G24 would cover 1 track of the 1" 8-track...and even then, I doubt the the actual position would line up perfectly, and as you say, the quality is not likely to be as good....so I kinda wonder if it is worth it, I mean, to go to all the trouble of recapping the G24 just to get some playback from it, knowing that the Dolby S chips are critical for actually ever recording with the deck....?
    Well, it looks like he does format conversion as a service, going by his signature I'd expect him to use the 2" deck for recording anything serious, so the G24 most likely is being used as a playback-only affair. What I did when transferring an 8-track tape on the MSR-24 was to record all 24 tracks, and pick the best from each triplet once it was in the computer.
    And yeah, an Otari MX70 with the 8-track head, a Soundcraft 381 or Brenell Mini-8 would certainly be closer to the mark, but all of those are pretty rare, and the MX70 is fairly large. I couldn't really justify buying one for a single master tape and I don't know how many he needs to transfer.

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    Quote Originally Posted by jpmorris View Post
    Well, it looks like he does format conversion as a service, going by his signature I'd expect him to use the 2" deck for recording anything serious, so the G24 most likely is being used as a playback-only affair. What I did when transferring an 8-track tape on the MSR-24 was to record all 24 tracks, and pick the best from each triplet once it was in the computer.
    And yeah, an Otari MX70 with the 8-track head, a Soundcraft 381 or Brenell Mini-8 would certainly be closer to the mark, but all of those are pretty rare, and the MX70 is fairly large. I couldn't really justify buying one for a single master tape and I don't know how many he needs to transfer.
    Yeah...I get all that...but it just seems like a lot of work to try and recap the G24 with its surface-mount components...just to end up with a less than perfect 8-track format transfer machine, that will be playback-only even after the overhaul.
    I can understand using the odd transfer format for maybe a tape or two, for private , non-critical use...but not if it's for a commercial transfer service., especially considering that the audio quality (and decision of using a 1" 8-track to record)...will be reduced with the smaller format G24, IMO.

    Anyway...it's his call, his transfer service and his time and effort repairing the G24...good luck, and let us know how it comes out!

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    Yes - this is a 1" 8 track tape that I'm trying to transfer. I don't get many 1" tapes coming through so I've not used the machine in a while although I try to remember to power it up every few months to keep the capacitors formed. I didn't know about the leaking capacitor issue until I started troubleshooting these problems. Fortunately in this case the client just wants to check that what is on the tape matches the label so I don't need every track working but I'm aiming to get 8 good tracks by the end of next week.

    I've just started this evening and so far I've replaced the obviously leaking capacitors on just 2 boards - this is going to be a slow process. However the machine is in good condition with very little head wear so this is worth pursuing I think.

    As far as the meters go, I have an oscilloscope if needed and the power supply voltages measure fine on a DVM but I think this could be some kind of strange timing issue with the analogue multiplexing - almost as if every second sample is missing. I was just being a bit lazy and hoping that someone might have seen this behaviour before. If you are interested it is probably worth looking at the service manual as the meters work somewhat differently from any other tape machine that I've encountered. The service manual can be found at FOSTEX G24S SERVICE MANUAL Pdf Download. although some of the component values don't completely agree with those on my machine.
    JRP Music - Audio Mastering and Restoration
    http://www.jrpmusic.co.uk

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