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Thread: 1980's Roland BN-100, Need schematic

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    Member spsimmons's Avatar
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    1980's Roland BN-100, Need schematic

    Hey guys, I have had this BN-100 bass amp for probably 15 years. It's really a great sounding amp, nice chorus, sweet 15" JBL speaker. My biggest problem with it is that is weighs 60 or 70 pounds, hell, maybe more. Real heavy.

    Anyway, I've had it in storage for about a year. I got it out yesterday to clean it and test it so that I could try to sell it. Wouldn't you know it, it makes no sound! It worked fine last time I used it.

    The lights come on and the speaker extends, but I get nothing from either input. There is no hiss, no crackle, nothing. Dead silent.

    After messing with it for a while, I plugged the bass into the effects return. The power amp seems to be working fine. Something is up with the pre-amp or there's a loose connection somewhere. Physical inspection and poking around with the chopstick didn't turn up anything.

    Anyone have a schematic for this amp? I think it came in a 60 watt version too (BN-60). Any ideas on things to check?

    Thanks, Shannon

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  2. #2
    don't forget the joker g1's Avatar
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    Connect the send to the return with a cord, then plug your bass in the regular input. Any better?

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    Member spsimmons's Avatar
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    Thanks, g-one. When I do as you suggest, I get the same eerie silence.

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    Quote Originally Posted by spsimmons View Post
    Hey guys, I have had this BN-100 bass amp for probably 15 years. It's really a great sounding amp, nice chorus, sweet 15" JBL speaker. My biggest problem with it is that is weighs 60 or 70 pounds, hell, maybe more. Real heavy.

    Anyway, I've had it in storage for about a year. I got it out yesterday to clean it and test it so that I could try to sell it. Wouldn't you know it, it makes no sound! It worked fine last time I used it.

    The lights come on and the speaker extends, but I get nothing from either input. There is no hiss, no crackle, nothing. Dead silent.

    After messing with it for a while, I plugged the bass into the effects return. The power amp seems to be working fine. Something is up with the pre-amp or there's a loose connection somewhere. Physical inspection and poking around with the chopstick didn't turn up anything.

    Anyone have a schematic for this amp? I think it came in a 60 watt version too (BN-60). Any ideas on things to check?

    Thanks, Shannon
    Good luck.
    Attached Files Attached Files

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    Thanks so much!

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    Senior Member mozwell's Avatar
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    First, check the power supplies, do you have -15V on IC2 pin 4, do you have +15V on pin 8 IC2
    Do you have +/-54V t the power amp
    Check out the connection CV, does this start off at 0V and ramp up to 15V ?

    Try thsi with teh chorus set to off, do you get sound now ?
    It looks like there are fets Q2, Q3, Q4 between the preamp & power amp. Try shorting out Drain to Source of Q3, do you get sound. It could be a faulty fet Q3
    If you don't use the chorus out socket, you could remove Q3, remove Q2 and solder it in the Q3 position

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    Member spsimmons's Avatar
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    I tried to do the checks that mozwell suggested.

    IC2 must be a controller for the EQ. With the EQ on, I get -.9vdc from pin 4 to ground and -130mvdc from pin 8 to ground.
    With the EQ bypassed, I get 14.98vdc from pin 4 to ground and -.55vdc from pin 8 to ground.

    I don't know where to check for the +/-54v at the power amp.

    I also don't know what "CV" refers to. I find it on the schematic (after D8 off of Q2 and after D11 off of Q4), but I'm having a hard time tracing it on the actual pcb.

    In my attempt to figure out what CV refers to I noticed that D8 is the chorus on/off indicator led. D8 is not lighting with the switch in either position.

    I'm a little stumped here. Usually when I open up a non-functional amp, I find loose connections and/or obviously damaged components. Furthermore, this amp worked when I put it in storage. I expected a loose connection.

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    As you said the power amp in works fine, you don't need to worry about the +/-54V.
    But IC2 shows there is a problem with the +/-15V.
    Pin 4 & 8 voltages should not change. Something that is engaged with the EQ switch is affecting the -15V, and probably the same thing is causing problems for the +15V.
    It could be some bad IC, or the +/-15 regulator circuits (Q103 & Q104 area).
    The "CV" is the control voltage that runs the mute circuit to avoid turn on thumps. It goes to the Q3 mute fet Mozwell mentioned.

    edit: you don't need to worry about the CV for now, without proper +/-15V, the preamp will not work. That must be sorted out first, and will probably be the only problem.

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    I just wanted to post an update to this thread. Amp is still not working.

    I get -15V on pin 4 of ICs 1-3.

    I get -5.9V on pin 8 of ICs 1-3

    I am getting -15V on pins 1 and 3 of Q104.

    I am getting readings of 300mV and -275mV on pins 1 and 3 of Q103.

    I pulled Q103 and did a diode test on it and to my (limited) knowledge it seems good.

    At the bridge rectifier I get the +/-55V that would be expected.

    Shorting pins 1 and 3 of Q3 has no effect.

    It seems curious to me that D8 (the chorus on/off indicator LED) doesn't function.

    I'm going to keep working through the circuit. I'm losing the +/-15V somewhere.

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    Last edited by spsimmons; 03-13-2015 at 03:13 AM. Reason: Posted bad readings

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    Supporting Member The Dude's Avatar
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    Quote Originally Posted by spsimmons View Post
    ... I'm not getting the expected +/-15V at pins 1 and 8 on any of the ICs (1-5) on the PA board.
    IC's 1-3 supply: pin 4 = -15 & pin 8 = +15.
    IC 4&5 supply: pin 8 = +15 & pin 4 gnd.

    No supply on pin 1 of these IC's. Is that just a typo, or are you perhaps looking at the wrong pins?

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    Last edited by The Dude; 03-13-2015 at 04:06 AM.
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    Supporting Member The Dude's Avatar
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    Unless I missed it,...... have you tried plugging a sound source into the main input jack to verify if the power amp works?

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    Member spsimmons's Avatar
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    Thanks, Dude. That was a screw up. I was incorrectly taking readings at pin 1. I have edited the info to reflect that the -15V is consistently correct and the +15V is consistently bad.

    When I plug a functional bass into the normal hi or lo inputs, I get no sound. When I plug the bass into the effects return, I get sound.

    Thanks again for pointing out my mistake.

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    Supporting Member The Dude's Avatar
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    If you temporarily lift the +15 connection from the amp board to the preamp board (Jumper from 2 to 10 on the schematic) does the +15 come up on the amp board (terminal 10)? This will help us determine if we have a regulator issue or excessive load on the preamp board.

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    Member spsimmons's Avatar
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    Just pulled D2 off the MA board. It's bad.

    This all has me wondering where the +/-15V originates from. Is it the result of running the +/-55V into the zener/resistor part of the circuit (D2,R3,R4 and D1,R1,R2)?

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    Lifetime Member Enzo's Avatar
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    You are missing +15v. Look at the power supply, Q103 is the pass transistor for it, and zener D2 sets the voltage. So is there about 16v across D2? And do what Dude suggested.

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    Member spsimmons's Avatar
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    I get a similar reading with the jumper wire lifted, about -260mV.

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    Lifetime Member Enzo's Avatar
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    OK, so the supply itself is bad, check the diode voltage and the transistor. Oh, and check that 330 ohm resistor feeding into the Q103 collector, R4, is it open?

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    Enzo, if by "across", you mean anode to cathode with the circuit energized, I get about -260mV in one direction and 0V in the other.

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    Member spsimmons's Avatar
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    R3 and R4 check out as good.

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    Supporting Member The Dude's Avatar
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    If you look, +VCC goes through R3 to D2 and C2. If D2 was replaced and R3 is good, C2 may be bad.

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    Lifetime Member Enzo's Avatar
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    Sorry, I missed your earlier post that D2 was bad.

    Zener diode puts 16v on the base of the pass transistor, the +50 comes through the 330 ohm to the transistor collector. The diode sets the voltage which results in about 15v on the emitter, the output of the supply.

    Scroll down to figure 3.
    Transistor-Zener Diode Regulator Circuits

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    Member spsimmons's Avatar
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    Unfortunately, I don't have the proper replacement for D2. Would it be worth swapping D1 and D2 as a test? Would that risk further damage to the circuit?

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  23. #23
    Supporting Member The Dude's Avatar
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    I would just wait. You'll have to get one anyway. FYI it's a 16V - 1/2W zener diode. The part number doesn't matter a whole lot as long as it fits these specs.

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    Member spsimmons's Avatar
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    Thanks guys. I've been putting together a list for a couple of other amps I've been working on. I think I have enough now to justify the shipping. I'll report back on this (and another thread) when I get it put back together.

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    Lifetime Member Enzo's Avatar
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    Do you have a 15v zener? A 1N4744? If so, stick it in there for now. It is only one volt off and will allow the work to continue. Put a proper one in later.

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    Member spsimmons's Avatar
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    I got a 16V zener from a local repair shop. After installing it the amp works again.

    I now get +13.9V on the 8 pin of the ICs and it remains constant. I get -14.5V on pin 4.

    Should I consider this to be within tolerance, or should I try to get the + voltage up closer to 15V?

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    Lifetime Member Enzo's Avatar
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    Close enough, it is just a guitar amp.

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    Member spsimmons's Avatar
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    That's funny, thanks. Thanks everyone! I'll bolt it back together.

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