Help fixing Boss DR-55 sequencer

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Re: Help fixing Boss DR-55 sequencer

Postby polysixer » Wed May 24, 2017 11:01 am

Mooger5 wrote:The cap keeps the memory charged for enough time to change batteries. Doubing the capacitance doubles the time it holds the charge. It was probably a factory mod...
Removing the cap and the diode at the same time erases the memory.
Same rhing if the duode is removed for too much time. You'll have to reprogram every pattern.
While doing so check the rhythm selector. Dirty contacts or a bad ground to the pull down resistors might interfere with the programming. And also the play back as the memory wouldnt know ehich pattern to replay from.
In the schematic where it says encoder measure the voltage at the three input terminals of ic1. While selecting the patterns. Zero volts is low and five volts is high.
Pattern one will be LLL PATTERN TWO WILL BE HLL THREE LHL, LLH HHL LHH HLH AND EIGTH WILL BE HHH.


One thing that still has me puzzled was that, when I checked for cold solder joints, for a brief time, I could store sounds in steps when in write mode. The rest of the time I can trigger the instruments properly (and hear CHs if they're set on) in write mode but not keep them in memory and listen to recorded steps. The different behaviour of CH triggering in play and write mode should tell me that switching is done correctly. Other than proper voltage feeding to the memory chip, what is responsible of keeping instruments recorded in steps?
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Re: Help fixing Boss DR-55 sequencer

Postby polysixer » Wed May 24, 2017 11:07 am

Mooger5 wrote:No problem. Also clraning the contacts in ebery vonnector might help too. Isnt there a pedal input or something, ig its for step advance or tap tempo it could be it. Good luck.


There's a foot switch input but it just works as start/stop for the existing clock, which doesn't seem to have problems.
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Re: Help fixing Boss DR-55 sequencer

Postby Mooger5 » Wed May 24, 2017 3:00 pm

I'll check the schematics later but maybe the fs input could be in conflict with the start stop buttons inplay mode. Much like the trigger in connector and the sequrncer in the sh101.
More later
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Re: Help fixing Boss DR-55 sequencer

Postby Mooger5 » Wed May 24, 2017 5:23 pm

polysixer wrote:Other than proper voltage feeding to the memory chip, what is responsible of keeping instruments recorded in steps?


The way I see it is that the chip doesn´t care about rhythms or instruments, right? It can output 4 bits at the same time and it has 256 memories. Every bit can be either hi or lo so that for example for memory nr.1 first bit is say hi, 2nd bit is say lo, 3rd bit is lo, 4th bit is hi. For memory nr2 1st bit is lo, 2nd bit is hi, 3rd bit is hi, 4th bit is hi, and so on. Now for every bit that is Hi, a single square wave pulse is output, which will trigger a synthesized sound or a vca. So the four bits are yhe three instruments and the accent function. You can access any memory any time and tell the chip in what state any bit will be. This is the Write function. The 256 memories are accessed through eight adress ports in binary mode. 2 (yes or no, hi or lo, zero or one) to the powers of eight (the number of adresses, or bits) equals 256.
So memory nr 1 will be HLLLLLLL, memory nr.2 will be LHLLLLLL, nr3 will be LLHLLLLL and so on. The last three bits, to the right, are chosen by the rhythm select encoder. The first four bits, counting from left, are "played" sequentially by the binary counter, which is triggered by the clock in play mode, or by the schmitt trigger in write mode. There´s a fifth bit in the memory adress which is the variation. This one I have no idea how it works.
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Re: Help fixing Boss DR-55 sequencer

Postby Mooger5 » Wed May 24, 2017 5:46 pm

As the counter works only with four bits there´s only 16 different memories it can count, because 2 to the powers of four equals 16. However there´s the rncoder which prvides eight additional numbers. So HLLL(L)LLL is a different memory number than HLLL(L)HLL. Those 16 memories it counts are the sixteen steps. After it reaches HHHH it goes back to LLLL.
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Re: Help fixing Boss DR-55 sequencer

Postby polysixer » Wed May 24, 2017 6:02 pm

Mooger5 wrote:
polysixer wrote:Other than proper voltage feeding to the memory chip, what is responsible of keeping instruments recorded in steps?


The way I see it is that the chip doesn´t care about rhythms or instruments, right? It can output 4 bits at the same time and it has 256 memories. Every bit can be either hi or lo so that for example for memory nr.1 first bit is say hi, 2nd bit is say lo, 3rd bit is lo, 4th bit is hi. For memory nr2 1st bit is lo, 2nd bit is hi, 3rd bit is hi, 4th bit is hi, and so on. Now for every bit that is Hi, a single square wave pulse is output, which will trigger a synthesized sound or a vca. So the four bits are yhe three instruments and the accent function. You can access any memory any time and tell the chip in what state any bit will be. This is the Write function. The 256 memories are accessed through eight adress ports in binary mode. 2 (yes or no, hi or lo, zero or one) to the powers of eight (the number of adresses, or bits) equals 256.
So memory nr 1 will be HLLLLLLL, memory nr.2 will be LHLLLLLL, nr3 will be LLHLLLLL and so on. The last three bits, to the right, are chosen by the rhythm select encoder. The first four bits, counting from left, are "played" sequentially by the binary counter, which is triggered by the clock in play mode, or by the schmitt trigger in write mode. There´s a fifth bit in the memory adress which is the variation. This one I have no idea how it works.


Got it. Thanks for the detailed explanation. I'll see if those levels get to the memory chip and post back.
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Re: Help fixing Boss DR-55 sequencer

Postby Mooger5 » Wed May 24, 2017 6:15 pm

Random behaviour suggests bad solder joints or dirty contacts. There´s a Mode switch S2. Which gets used a lot, right? Dirt and grease might create a capacitive coupling between the contacts and with the unit in play mode, with the clock running etc it might tell IC1 it´s still in write mode, IDK.

I haven´t figured out how in write mode how IC1 is told the selected bit (instrument) to be either hi or lo. It´s by means of S1, but exactly how, IDK.
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Re: Help fixing Boss DR-55 sequencer

Postby polysixer » Wed May 24, 2017 6:28 pm

Mooger5 wrote:Random behaviour suggests bad solder joints or dirty contacts. There´s a Mode switch S2. Which gets used a lot, right? Dirt and grease might create a capacitive coupling between the contacts and with the unit in play mode, with the clock running etc it might tell IC1 it´s still in write mode, IDK.

I haven´t figured out how in write mode how IC1 is told the selected bit (instrument) to be either hi or lo. It´s by means of S1, but exactly how, IDK.



Yes, I'm getting the corresponding Hi and Lo levels (in voltage peaks) changing pattern numbers, at terminals 1,2 and 4 (from encoder section) and 3,4,5,6 and 7 from the binary counter, so that looks fine. I've also thought of disassembling and cleaning Mode switch S2, that's my best bet for now.
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Re: Help fixing Boss DR-55 sequencer

Postby Mooger5 » Wed May 24, 2017 6:35 pm

I know it sounds weird but I´m having fun learning all this :D

In the typical application shown in this datasheet http://www.spinsemi.com/Products/datash ... 1/FV-1.pdf
there are 8 programs stored in memory. Accessed by the three switches. I was looking for a method to select the progams using a conventional rotary switch and now, thanks to the Rhythm Select encoder schematic of the DR55, I know how to make it. So by helping others I help myself too :)

Cheers!
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Re: Help fixing Boss DR-55 sequencer

Postby polysixer » Wed May 24, 2017 8:24 pm

Mooger5 wrote:I know it sounds weird but I´m having fun learning all this :D

In the typical application shown in this datasheet http://www.spinsemi.com/Products/datash ... 1/FV-1.pdf
there are 8 programs stored in memory. Accessed by the three switches. I was looking for a method to select the progams using a conventional rotary switch and now, thanks to the Rhythm Select encoder schematic of the DR55, I know how to make it. So by helping others I help myself too :)

Cheers!


That's awesome to hear!

It awesome too that I've found the culprit: the previous owner attached a resistor to one of the legs of SW2, as shown in the attached pic. My thinking was that it was a factory modification. Why they did this I have no idea, but desoldering it has made everything work again. Now, the memory only holds the pattern for some minutes after turning power off, but that's probably my fault for switching a 47uf cap to the service notes 22uf cap. I think the first value should solve it.

Image

Mystery solved I think, we've all learned a few things from this funky machine. Again, thanks a lot for your input and support.
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Re: Help fixing Boss DR-55 sequencer

Postby Mooger5 » Wed May 24, 2017 10:09 pm

Now THAT´S awesome! Congrats!

I think though, the patterns should not be lost a few minutes after turning off the unit. The first value will only delay it a few more minutes, it´s the role of the cap to serve as power backup while the batteries are temporarily removed. CMOS devices waste very little current, but the cap will eventually discharge and the memory will be erased if fresh batteries aren´t installed. Removing the cap and the batteries and the memory is erased immediately after power off.

The batteries should be connected to IC1 at all times including after power off. They will act just like the usual coin cells.

There´s the audio output connector which has a built-in switch. The power line goes through it. When the audio cable is unplugged it disconnects the battery pack from the waveshapers and audio opamps etc, leaving just the logic section powered on. This saves battery life. It´s how it should work.
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Re: Help fixing Boss DR-55 sequencer

Postby polysixer » Thu May 25, 2017 12:57 am

Mooger5 wrote:Now THAT´S awesome! Congrats!

I think though, the patterns should not be lost a few minutes after turning off the unit. The first value will only delay it a few more minutes, it´s the role of the cap to serve as power backup while the batteries are temporarily removed. CMOS devices waste very little current, but the cap will eventually discharge and the memory will be erased if fresh batteries aren´t installed. Removing the cap and the batteries and the memory is erased immediately after power off.

The batteries should be connected to IC1 at all times including after power off. They will act just like the usual coin cells.

There´s the audio output connector which has a built-in switch. The power line goes through it. When the audio cable is unplugged it disconnects the battery pack from the waveshapers and audio opamps etc, leaving just the logic section powered on. This saves battery life. It´s how it should work.


Colophon: of course the random erasing was a switch problem. S2 was making a bad contact inside, switching some tracks to Play and others to write, so when I played a pattern, the bad contact switched to write mode would erase beats, as no notes can be entered in that mode. A quick disassembly of the switch, clean inside and put the small contacts in place and it's now happily saving all patterns with or without being powered on! A happy ending for me and I hope it can help others. A non working sequencer from this unit can easily be fixed this way.
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Re: Help fixing Boss DR-55 sequencer

Postby JHatzia » Thu Sep 14, 2017 3:27 am

I have a Dr-55 with a somewhat similar issue. It's alway stuck on in play mode and always seems to have a rim shot playing in on every step. In write mode both switches trigger the sounds yet seem to write it to the memory. I can't erase steps when both triggers do this. When I switch back to Play mode sometimes the pattern is saved but then it quickly fades away to the unaccented rims on each step. So it seems like sometimes it will save the pattern but only momentarily at best. All sound generation, knobs and switches seem to all work fine.

Two other people had a crack at this unit so here's a quick run down.

  • 052-537 PCB Version
  • The unit was received in this condition
  • All ICs have been socketed and swapped w no change in behavior
  • All electrolytic capacitors have been replaced
  • The last person who attempted fixing it removed R77 thinking it was a mod. The SM lists R77 as R100 resistor but it looks like mine had a 1K resistor. Can anyone confirm if a 1K resistor works. What exactly is a R100 resistor?
  • A lifted trace between C18 and a jumper have been patched with copper wire
  • The Stop switch itself has a pin that doesn't have a pad. Is this normal?

EDIT: I've been reading the SM and using a logic probe and found some interesting results.

3 SCHIMITT TRIGGER (Q15, 17, 18)
This circuit functions in WRITE mode only. The collector of Q15 goes
H when either the START switch S5 or the STOP switch S6 is turned ON, and goes to L when the switch set to ON is turned OFF.

15 and 18 behave this way but Q17's collector acts opposite. So it rests at H and goes L when Start/Stop are triggered. This mode also works for in Play mode unlike what the SM says. Maybe this can help narrow this issue.
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Re: Help fixing Boss DR-55 sequencer

Postby JHatzia » Fri Sep 15, 2017 10:12 pm

I was able to make some progress. Turns out the "tech" I let hold onto my Dr-55 for well over a year removed R77 saying it was a mod. Well it wasn't, it's actually a 1K resistor that is suppose to go from IC1 Pin6 to Wire 6. This immediately made the sequencer start/stop properly.

Programming patterns now works completely, but they are still not writing to the memory. Also, there is still the pulse or quite rimshot sound playing every step in Play Mode.

Progress.
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