Beocord 7000 voltage issues

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  • #11132
    Die_Bogener
    BRONZE Member
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    Check the 7805 power regulator… there musst be 5V. These 5V switch TR5 on.

    And test 92 R1 !… it could be a thermal resistor inside the transformer.

    #11137
    alf
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    Ok, strange things but:

    I replaced the 5V regulator for good measure but it does not get any decent voltage input nor would it then deliver the required 5V.

    the 1.5ohm resistor at the transformer measures spot on.
    The voltage at D3/D4 is about 28.8VDC and D6/D8 is about 6.1VDC which is a new development.

    I also checked for injured tracks – all seem fine but I can’t work out why the 5V regulator isn’t getting enough ??

    ALF

    #11164
    alf
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    Had another look at the PS to see why the 5V regulator isn’t getting enough voltage at its input.

    there is a resistor R11 = 22MOhm (?) which can’t be found in any of the circuit diagrams listed and I begin to wonder if that resistor is actually out of spec, showing about 6VDC on the entry side and next to nothing at the lead up to the regulator input?

    was the circuit diagram altered for the BC7000 model ? Martin might know ?!

    ALF

    #11171
    alf
    BRONZE Member
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    Had another look at the PS to see why the 5V regulator isn’t getting enough voltage at its input.

    there is a resistor R11 about 1MOhm (?) which can’t be found in any of the circuit diagrams listed and I begin to wonder if that resistor is actually out of spec, showing about 6VDC on the entry side and next to nothing at the lead up to the regulator input?

    was the circuit diagram altered for the BC7000 model ? Martin might know ?!

    looking at the IC7805 spec sheet its input voltage should be 7 – 25 V, so R11 would act as a input voltage limiter for IC7805 , correct ?

    ALF

    #11172
    alf
    BRONZE Member
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    Sorry about the double reply – the last one is the one that should be there.

    ALF

    #11182
    Dillen
    Moderator
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    A 1M resistor would not be a “voltage limiter”, and it won’t be in series with the supply in any way as even the smallest current would result in a huge voltage drop across it.
    Could be a bleeder or a coupling to another part of the supply – but don’t worry about this resistor at this point.

    Set your meter to DC volts.
    Clip your meters negative lead to the negative pin on C3.

    With the positive lead please take readings on
    – C3 positive lead
    – IC1 all three pins respectively
    – TR5 all three pins respectively

    Martin

    #11229
    alf
    BRONZE Member
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    Thise measurements are as follows:

    C3+  = 28.8 VDC

    IC1  In=112 mVDC,  G=0, Out=0

    3TR5. E=0.130 VDC , C=0.220 unsteady jumping, B= 0

    just an observation:

    looking at the PS board of BC5500 I see a jumper in series connecting the track coming from rectifier to Input of IC1 instead of a resistor (R11?)

    this board looks exactly the same as the one for the BC7000 except no jumper but R11?

    ALF

     

     

    #11237
    alf
    BRONZE Member
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    Some minor development:

    after the previous measurements it all made no sense. I took out that mysterious R11

    and measured it…..OL !! Which explains why IC1 did not deliver the 5V.

    i can not identify that resistors value as its colour markings made no sense – discoloured ??

    I decided to replace the dead resistor with a 690 Ohm one for now which seemed ok as the BC5500 board just has a jumper in that position.

    the display lights up, the drawer closes but shortly after the deck shuts off again.

    the drive does not engage……meaning there is still lots more to check….☹️

    ALF

     

    #11242
    Dillen
    Moderator
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    I can’t find any mentioning of this resistor in my notes, but if it sits in series with the
    supply to the regulator it is far more likely to be a 4,7ohm or similar value.
    And it should be a flame-proof type.

    Martin

    #11246
    alf
    BRONZE Member
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    i will have a second look at the colour rings of that resistor but the 4…..? could

    indeed be right ?!

    lots of other corners to check – the drive itself could have issues as well, although the capstan runs if fed by the benchtop dc power supply.

    ALF

    #11389
    alf
    BRONZE Member
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    I am trying to follow the 12V entry for the drive, which I should measure at p16-4…..

    but nothing anywhere near it.

    I should also see 12V at the “emitter crosspoint” of TR37 and TR38…..nothing again.

    both Transistors have been tested off-board as ok which made me believe I should actually see the 12VDC at that crossing or shouldn’t I ?!

    i can see the entry voltages – 14.1V & 15.5V – at R171 and R172 …..so, what is it that I am missing here and why isn’t the capstan getting the 12V either.

    the drive unit looks like being hard-wired to the control board #2.

    ALF

     

     

     

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