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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 1st Apr 2019, 9:35 pm   #1
NorfolkDaveUK
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Default Dokorder 7100 no pinch roller.

Hi all ,

I have a Dokorder 7100 with no pinch roller activation , I`ve looked at the trasistors on the little break out board under the control board and all is well there as far as working componants go (as far as i can tell ) . I have the service manual but it gives me no voltages to check on the schematic , can any one assist me with it by any chance ?
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Old 2nd Apr 2019, 12:37 am   #2
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Default Re: Dokorder 7100 no pinch roller.

After some head scratching , I`ve noticed that there are a couple of other issues also .
When i lift the EOT arm , the brakes release but they are free wheeling , no back tension at all . Also the pause switch is inactive (i`m assuming it will be until the pinch roller activates though ) , also the record lights and/or switches don`t work I dont know if this is related (I doubt it , its probably something I`ll have to sort after the transport issues )

I`ve tested all the micro switches and they all work ok . I`m really scratching my head because I dont know what voltages should be where .
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Old 2nd Apr 2019, 10:15 am   #3
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Default Re: Dokorder 7100 no pinch roller.

These units were more popular stateside. Might be worth asking on US forums.

I would certainly start by looking for missing voltages on or around the logic circuits.
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Old 2nd Apr 2019, 11:31 am   #4
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Default Re: Dokorder 7100 no pinch roller.

Thanks Ben , yeah the circuit in question is the one in the pic. It looks to me like two identical circuits , one for the brakes and one for the pinch roller . The breaks are working disengaging , but not when they should , they disengage as soon as you lift the EOT arm so thats not at all right . The record lights work , but as soon as you hit the play and record buttons the lights go out , and of course the pinch roller doesn`t activate at all . I`ve checked all the marked voltages on the schematic and they are all correct , BUT , going back to the circuit in the pic , they aren`t showing the same voltages at the transistors . I wish I could post the whole schematic , but I cant because I paid for it and it came with the "do not post on forums" proviso . I`ll get the voltages in a sec and tell you what they are when its in play . All of the transistors test ok (ooc) and the diodes also
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Old 2nd Apr 2019, 4:12 pm   #5
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Default Re: Dokorder 7100 no pinch roller.

Progress : The previous owner has put the 18 pin connector on the back of the transport panel on upside down (doh) , and of course I didnt check , so , NOW I have put that back on as its supposed to be , everything is working BUT for the pinch roller . Brakes now work as they should , record lights are now fine , if I manually manipulate the pinch roller all switches related to it are working . SO , now Its making a lot more sense and I can now work on the problem in hand .
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Old 2nd Apr 2019, 7:02 pm   #6
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Default Re: Dokorder 7100 no pinch roller.

ALL DONE .... soldered the wires directly onto the transport board and that fixed it . Plug was knackered !
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Old 2nd Apr 2019, 10:07 pm   #7
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Default Re: Dokorder 7100 no pinch roller.

Great news! Human error combined with connection trouble can give rise to some odd symptoms. This seems like an intetresting deck, any chance of some pics?
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Old 3rd Apr 2019, 10:52 am   #8
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Default Re: Dokorder 7100 no pinch roller.

Quote:
Originally Posted by ben View Post
Great news! Human error combined with connection trouble can give rise to some odd symptoms. This seems like an intetresting deck, any chance of some pics?
Sure . The funny thing is , after all the hassle . I got it going , went to calibrate it and it was 100% still in spec. I was floored . Not only that it sounds really good . Its not a studer by any stretch of the imagination , and the knobs are crap at best but sound wise I`m really impressed with it . I`ll take some internal pics in a min
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Old 3rd Apr 2019, 1:24 pm   #9
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Default Re: Dokorder 7100 no pinch roller.

Here you go , some internal pics , pic 3 is the repair of the broken bakelite connector. 3 motor , 3 head , pretty nice really .
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Old 4th Apr 2019, 1:47 am   #10
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Default Re: Dokorder 7100 no pinch roller.

Thanks for the pics. Nice simple uncluttered face plate. Has the look of Braun or NAD about it. The inside reminds me of my Sonys (TC755 , Tc766) quite a bit of wire in there but okay if you know what you're looking for and have a schematic.
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Old 15th Apr 2019, 9:28 pm   #11
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Default Re: Dokorder 7100 no pinch roller.

As this tape recorder is now on eBay I'll close this thread.
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