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Thread: Behringer DSP-8024 Help Needed

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    Behringer DSP-8024 Help Needed

    Hello,
    I have a DSP-8024 that won't boot up past the "Welcome' message. In addition to the message it will flash the various LED's back and forth. One of the large power supply caps was bulged so I replaced all three of the large ones and a few of the nearby smaller ones even though they tested OK.

    I've tried three different backup batteries with no luck. Are there know issues with the PS on these? I'm thinking it maybe the EEPROM? The firmware is
    ver. 1.3. Are there a 1.3a and 1.3b revisions? I've seen both mentioned on the Internet.

    I know there is a protection mode with the relays. They never kick in on mine. I've also looked for cold solder joints etc.

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    Lifetime Member Enzo's Avatar
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    First check power supplies. You replaced bulged caps, but do each of those caps have a nice smooth DC voltage? The relay doesn;t kick in because it never finishes its wakeup sequence. My first suspect is excess ripple or low voltage on one of the computer voltages.

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    Old Timer km6xz's Avatar
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    Did the backup battery need replacing? If not, why risk introducing more unintended problems before figuring out the real problem?
    Guesses in the dark and swapping out good parts will only make repair harder and less likely. Don't change anything unless you can prove that it needs it. Do as Enzo says, check the power supply output for voltage and ripple on a scope, it is the most likely cause of this problem. Leave the EPROM's alone, it is extremely rare for one to fail, it is NOT a version issue.
    Verify the clocks are of the right amplitude and frequency with a scope.

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    Noodle of Reality Steve Conner's Avatar
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    Did you try the factory reset procedure? If it didn't need a factory reset before, it probably will now that you've messed with the backup battery.

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    Quote Originally Posted by km6xz View Post
    Leave the EPROM's alone, it is extremely rare for one to fail, it is NOT a version issue.
    Verify the clocks are of the right amplitude and frequency with a scope.
    +1

    And double check all the PSU voltages first,
    As it seems schems are rare or non existent.....some inside pics could help .

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    OK, checked for AC Ripple and DCV.

    Out of the PT are two sets of secondaries. One is center tapped for the 7915/7815, the other is a pair marked on the PCB "AC" and "Cm" for common I suppose. This set goes to a LM317

    AC voltages out of the PT. 20.24/20.24vac for the CT, 6.06vac/0.50vac the other.

    7915: G=0, Vin=-25.76vdc, Vout=-15.06vdc with 129mv AC ripple on Vin.

    7815: Vin=24.00vdc, G=0, Vout=15.23vdc with 50mv of ripple on Vin

    LM317: ADJ=3.84vdc, Vout=5.1vdc, Vin= 13.25vdc with 1.35Vac ripple.

    The Vin on the 7915 shows continuity to ground sometimes then a cap will charge the meter. The three legs of the CT secondary at the PCB also show continuity to ground. Leaky 7915 maybe or the IN400x diodes?

    Now I did manage to get it to boot all the way up and fiddle with the programs etc. This was after I had pulled the board and replaced two small 10uf/50V bypass caps just for grins. They measured OK on my cap meter.

    I installed the board back with just one non grounded PCB screw, the the three screws holding down the regulators to the heat sink and the PCB to chassis ground wire.
    I let it run for quite awhile then prodded the ground wire with a chop stick and it went back to the protection mode. I checked that wire for continuity. It looks OK.

    Per the manual pulling the battery is how these are reset. It will still work without, you'll just lose your settings.

    I'll get some pics up soon.

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    Last edited by Tejaus; 09-12-2012 at 01:19 AM.

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    Lifetime Member Enzo's Avatar
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    Your 15v supplies produce 15v, so the transformer is working. The leads from the CT winding show continuity to ground because the CT is grounded, and the winding is wire after all. That is OK.


    If poking a wire causes a symptom to either start or stop, then that poking esxposed some loose connection. It may not be that wire itself. When you poke the wire, you also put a little yank on th circuit board.

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    Thanks, that narrows it down a bit. I double checked the ground wire. sprayed a little Deoxit on it too.

    I'm going to clean the ground pads on the pcb tomorrow. And the tops of the standoffs.


    What about the 7915 Vin leg sometimes showing ground?
    And the 1.35vac on the LM317?

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    Lifetime Member Enzo's Avatar
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    The 1.35AC is ripple on the INPUT to the 317.

    You have a circuit full of capacitors, and when you measure resistance with your meter, the current the meter uses tries to charge the caps around it. The less charge there is in a cap, the more it looks like a short circuit. Plus polarity matters. If you try to measure resistance and there is a tiny residual charge voltage in the circuit, then your meter curent has to first discharge that voltage and then charge it up the other way.

    Grab an electrolytic cap from your parts supply. Measure its resistance with your meter. It will start low, then slowly go up as the cap charges. Now swap ends with your meter leads. I bet your meter starts out showing "negative resistance." SOmething meaningless like -12k ohms. That slowly drops to zero, then it starts climbing with regular resistance readings. Another paret of this experiment is to measure resistance of thgis cap until it stops going up. Now flip your meter over to DC volts and see what is now stored in the cap.

    If your three power supplies are making their nominal voltages and clean, and they do it every time you power up, then I wouldn;t worry about meter anomalies.

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    Well I re-flowed the solder on the PCB ground pads and made sure the PCB ground wire was firmly attached to the chassis. It worked for awhile and I left it running for about ten minutes. I could turn it on and off. I then turned it off to let it cool down and now it's not working again.

    Any idea on what the fault protection circuit is on this?

    From the Owners Manual:

    Fail-safe relays have been incorporated into the design of the BEHRINGER ULTRA-CURVE PRO, which
    automatically and silently bypass the unit in the event of power supply disconnection or failure. These relays
    are also active at switch-on to isolate the ULTRA-CURVE PRO until the power rails have settled, thus preventing
    the possibility of a potentially damaging switch-on thump.


    Click image for larger version. 

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    Last edited by Tejaus; 09-12-2012 at 10:21 PM.

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    Old Timer km6xz's Avatar
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    Maybe I missed it but before resoldering, did you check if the 3 clock oscillators are running? The intermittent nature of the problem sure sounds like a crystal oscillator not firing up each time. The phase shift chip caps on the crystals are suspect but occasionally it is the quartz crystal itself. Check with a high Z scope probe and note the relative amplitude. If one is much lower than the others it might be running on the wrong overtone.

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    Lifetime Member Enzo's Avatar
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    The relays connect input and output jacks, they have nothing to do with making it wake up when powered.

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    OK I put a probe on the the three crystals. The one on the far left doesn't show anything, the other two do. When I put the oscope probe on the far right one the LED's will halt flashing until I remove it.

    There are three different frequencies. Raltron branded.
    I think this is the right spec sheet:
    http://www.raltron.com/products/pdfs...c_49_45_51.pdf

    The one that is not showing a signal is marked:

    Raltron
    11.2986-20
    02NK38

    Middle one:
    Raltron
    12.288-20
    02NK38

    Right one by the PS:
    Raltron
    12.000-20
    02NK05

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    I can find the 11.2896 Mhz crystals at Mouser but not in the HC-49/U case, just the shorter version http://cfm.citizen.co.jp/english/pro.../HC-49_U-S.pdf

    Would that matter spec wise?

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    Old Timer olddawg's Avatar
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    Quote Originally Posted by Tejaus View Post
    OK I put a probe on the the three crystals. The one on the far left doesn't show anything, the other two do. When I put the oscope probe on the far right one the LED's will halt flashing until I
    02NK05
    Without a flow chart it is hard to tell, but that third crystal may not start running until the system wakes up. I would resolder that crystal being aware that is probably a double sided board. Once that is done, if it doesn't work, tickle it with some freeze mist. If you have a pinout on the micro look for the reset pin. Is it a - or + reset. You can usually do a manual reset by momentarily grounding the pin through a 1k resistor or to the 5v supply. You need 3 things: power, clock, and reset. If you have a scope you monitor the reset pulse.

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    Old Timer km6xz's Avatar
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    Don't replace the crystal until you prove it is faulty. Every time you or anyone, changes parts randomly or semi-randomly, the clear diagnosis becomes more ambiguous and less likely to be repaired successfully.
    Try injecting 11.2896 into the processor port. If a crystal fails to oscillate it is not high odds that it is the crystal. The crystal is an extremely high Q reactive resonate network and requires three things to begin and sustain oscillation, gain, noise and phase shift. The chip is connected to supplies the gain and therefore the noise and the two chip caps mounted next to the crystal provide the phase shift. Any leakage or value change in either of those caps can prevent sustained operation.

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    Lifetime Member Enzo's Avatar
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    And just for old school sake, any crystal that doesn;t want to sing, sometimes will start up if you rap on it. Use a plastic screwdriver handle or something. Oh. doesn;t always work of course, but it takes seconds.

    Oh...

    The 11.xxxMHz and 12.xxxMHz rocks are not oscillators, they are bare crystals. Yes they are in oscillator circuits, but they are not the little oscillator circuit cans. Q2 and Q3. Each is driven by a gate in IC45, a 74HC00. Further, each of those gates is controlled by another gate as an inverter, so ONLY ONE of them will oscillate at a time as selected by control signal MSEL at IC45-1 . Then the two outputs are ORed together by another gate in the IC, so whichever one is selected ultimately comes out IC45-8. If you have clock at IC45-8, then they are all working, at least enough. As far as I can tell, both are free running when selected. One or the other should always be going, but never both.

    Crystal Q1 is 12.0MHz and is also a crystal, not an oscillator, it is directly driven by IC36.

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    Is there a schematic available?

    I did resolder the crystals, no luck. The amplitude on the crystal located right by the PS was lower in amplitude than the middle one.

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    Here's a pic of the MHS S-80C31-16 microprocessor.
    http://www.datasheetcatalog.org/data...c/mXyzuzvq.pdf

    The index corner is on the bottom left of the chip in the pic.
    The RESET pad is tied to Pin 4:

    RST
    A high level on this for two machine cycles while the
    oscillator is running resets the device. An internal
    pull-down resistor permits Power-On reset using only a
    capacitor connected to VCC. As soon as the Reset is
    applied (Vin), PORT 1, 2 and 3 are tied to one. This
    operation is achieved asynchronously even if the
    oscillator does not start-up.

    The left pad of the two smaller pads to the right of the cap is tied to Pin 10. It has 5.0Vdc on it. The other is ground.

    TD (Timer 0 external input)

    The 10uf/50v cap is OK. I put a meter on the little 22pf caps and the seem OK. After doing that it booted up and ran for awhile. I did short a resistor fro the RESET pad to ground. Nothing happened. Should I short the reset to the 5.0vdc?

    Click image for larger version. 

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    Seems to be acting in intermittent mode,so it actually boots !,flexing the board may help.......
    I would reflow the processor as a starting point.
    Then if that fails repace the xtal(s) attached to it...or the other way round ,if you don't fancy a reflow,?
    Then take it from there.

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    Re-flowed the processor. It started up and I thought that fixed it. But then it went back to flashing the LED's. One thing it does when it does boot up all the way is display a message of Bad Check Sum Error, Memory Cleared. If I turn it off and and it boots back up fully it doesn't show that message again however.

    I've tried flexing the board doesn't seem to make a difference. I'm thinking it's a weak output from the xtal. On the scope it's amplitude is 0.34v compared to the middle xtal's 0.90v.

    Update: Found some 12.000Mhz HC-49U on ebay.

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    Last edited by Tejaus; 09-14-2012 at 04:50 PM.

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    The DSP-8024 seems to be acting just like the mixers in this thread. http://music-electronics-forum.com/t24165/

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    Old Timer olddawg's Avatar
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    I hate to say it. But this is begining to sound like a double sided board with an intermitant feed through. You may never find it. If you have a circuit viewer type microscope it would help. Did you reflow the processor using flux?

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    I have some flux that came with a Chip Quik kit. I could try that I suppose. It's pretty hard to trace out the board even with some 2x readers and a magnifying glass LOL.
    A schemo would be so helpful.

    I've tried flexing the board and freeze spraying it. It doesn't seem to make it stop or start. I'm tending to think the xtal is flaky. It's signal is about 1/3 the amplitude relative to the middle one.

    I bought some 12MHZ xtals off ebay, should be here next week.

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    Old Timer olddawg's Avatar
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    Spend $3 and get a bottle of flux and a small brush. I used to repair a lot of boards using a Hako hot air extractor machine with a single tube tip. Have you tried tickling the crystal with freeze mist. My guess would be that the other crystals are on 5v supplies and that at one is on 3v. Just a guess but fairly common.

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    Old Timer km6xz's Avatar
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    The symptoms do not sound like a bad plate through hole, few of the chips are through hole so the vias and header connectors are about the only parts of that portion of the circuit that is impacted. I never really saw a problem with board plating on Behringer gear, in fact other than physical damage to a board, I do not remember ever having a defect that was related to the board itself and that means many thousands of repairs since for some time we were the only warrant service center west of NYC.

    The rest test with the external pull down resistor tells you nothing other than the internal pull down is working as intended.

    The amplitude of the oscillator needs to be around 0.5s for reliable operation and there is a good chance that what is being seen is loading on the high z circuit by the probe. If the clock is starting reliably, kicking in as soon as power is applied, it is not likely the xtal. The output of the clock will be at normal CMOS levels and should be 5v peak, regardless of what is seen across the xtal.

    A clue as to the condition of the crystal would be measuring the frequency by comparing with a stable generator. You know it is oscillating and a counter would average jitter if it is unstable, so use a stable RF generator, preferably one that does not depend on a PLL which would have its own jitter, eiher DDS or a LC oscillator and compare the clock out in an XY mode on the scope to see if the cock is jumping all over. A xtal is so easy to verify if it is OK that is seems like a waste of time to keep replacing parts that are probably good. It also introduces ambiguity to the diagnosis. Rather than replacing things, diagnosis it. Repair and replacement of proven defective parts comes later.

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    Noodle of Reality Steve Conner's Avatar
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    The problems with the mixers were caused by a bad 32.768kHz crystal. Are you sure you don't have one of those that you've overlooked? It looks different to the other crystals, a tiny, long, thin, cylindrical silver can with two leads coming out of one end.

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    Spend $3 and get a bottle of flux and a small brush. I used to repair a lot of boards using a Hako hot air extractor machine with a single tube tip. Have you tried tickling the crystal with freeze mist. My guess would be that the other crystals are on 5v supplies and that at one is on 3v. Just a guess but fairly common.

    I tried the Chip Quik flux on the MP pins, worked great. Shot the MP and xtal with freeze spray, no effect.

    A clue as to the condition of the crystal would be measuring the frequency by comparing with a stable generator. You know it is oscillating and a counter would average jitter if it is unstable, so use a stable RF generator, preferably one that does not depend on a PLL which would have its own jitter, eiher DDS or a LC oscillator and compare the clock out in an XY mode on the scope to see if the cock is jumping all over. A xtal is so easy to verify if it is OK that is seems like a waste of time to keep replacing parts that are probably good. It also introduces ambiguity to the diagnosis. Rather than replacing things, diagnosis it. Repair and replacement of proven defective parts comes later.


    I have a Leader LAG-125 generator that will probably work. Low Distortion Audio Generator LAG-125 Equipment Leader Elec
    But please forgive me as I'm a first class noob with oscopes. With this being intermittent it's hard to find what is and is not defective. Do you know how the fault protection circuit trips? That's what seems to be happening.

    The problems with the mixers were caused by a bad 32.768kHz crystal. Are you sure you don't have one of those that you've overlooked? It looks different to the other crystals, a tiny, long, thin, cylindrical silver can with two leads coming out of one end.


    Nah, it just has those HC-49U case xtals. I have 5 on the way from ebay for 3.00 bucks.

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    Since this post didn't get resolved it appears I thought I might add a bit of what I experienced with this same unit.
    After checking the PS voltages and ripple, I found that if I leave it turned on for a while, 30 minutes or so with the lights flashing,
    then turn it off and back on again, the symptom seems to disappear and I am able to control the unit as normal.
    It may help to hold the IN/OUT button down when turning it back on again
    Hope this helps.
    My guess is that this indicates the problem may be a leaky cap.

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