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 Forum index » DIY Hardware and Software
Sequential Circuits Drumtraks Schematic
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defog



Joined: Aug 24, 2011
Posts: 113
Location: Philadelphia

PostPosted: Fri Dec 23, 2011 6:48 am    Post subject: Sequential Circuits Drumtraks Schematic Reply with quote  Mark this post and the followings unread

Hey guys,

I'm trying to repair/troubleshoot a Sequential Circuits Drumtraks and I can't for the life of me find the schematics anywhere online. I've done quite a bit of digging. Anyone have a PDF of this?

I'm trying to rebuild the power supply and get some basic information on some of the more rare ICs, and there is little to no information on some of these parts.

Thanks
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EdisonRex
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PostPosted: Fri Dec 23, 2011 4:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

which obscure chips do you need data sheets on?
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defog



Joined: Aug 24, 2011
Posts: 113
Location: Philadelphia

PostPosted: Fri Dec 23, 2011 8:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

EdisonRex wrote:
which obscure chips do you need data sheets on?


Thanks for the reply,

The main issue is that the Drumtraks doesn't boot up. The digital display never comes on, even though all Vcc connections are correct on all of the OpAmps and Logic ICs on the main board. I've done trace checks on all of the connection points and they are good. When I probed with my scope on the power section, I didn't see any significant noise on the voltage outputs of the regulators, but I am somewhat new to using a scope.

In the power supply section, the power rectifying diodes are marked T B-4. Googling was vague and best, suggesting they were zener diodes, but that can't be right. It looks like a normal full wave rectifier setup. I need an equivalent for those. I was going to rebuild with 1n4007s, but better safe than sorry. Also I've had trouble hunting down information on the TA78L. All the data sheets I googled were dead ends.

On the main board there are two ICs in particular that I can't find information on. There is a MC68B50P, which appears to be some sort of data bus IC and a D8253c-2 IC, which handles timing apparently. I don't know the functionality or pinout of either for certain, so I'm making educated guesses on them. I haven't been able to read bits with the scope on either, it's just noisy looking. Rebuilding the power supply seems like a good idea regardless, considering the age of the unit and the 4 tantalum caps on it.
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EdisonRex
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PostPosted: Sat Dec 24, 2011 6:35 am    Post subject: Reply with quote  Mark this post and the followings unread

You tried http://www.datasheetarchive.com/MC68B50P-datasheet.html ?

http://www.datasheetarchive.com/D8253C-2-datasheet.html ?

http://www.datasheetarchive.com/TA78-datasheet.html ... after L should be another number with the voltage. They even have application notes there.

I've downloaded data sheets so if for some reason you still cannot, they can be got to you. Those are old chips and are probably hard to find, but they may not even be the problem.

Rebuilding the PSU is likely to help a lot. I'm guessing "TB 4" isn't getting you anywhere and Google is suggesting a 4120 zener which you're right, that's not correct.

Probably good to replace the tantalums first. You might have others on the data board too. I'm not familiar with the innards of this beast but there might be a battery or something needing a replacement too.

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EdisonRex
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PostPosted: Sat Dec 24, 2011 6:44 am    Post subject: Reply with quote  Mark this post and the followings unread

And yes, there is an internal battery. Check for leakage around it. Replace it in any case, it's over 20 years old. If it isn't there, that's a problem too.
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defog



Joined: Aug 24, 2011
Posts: 113
Location: Philadelphia

PostPosted: Sun Dec 25, 2011 8:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

First thing I did was that battery replacement. I'm all too familiar with leakage damaging traces on boards I've repaired. Luckily, this one was in good shape, but it needed it, as the voltage was low on the battery.

I'm going to start with replacing the filter caps, tanatalums, and voltage regulators. I removed those diodes marks B4, and they all seemed to be in good shape, so I'm going to leave them in the circuit. Hopefully once the power section is rebuilt, I'll be able to confidently move onto probing the digital portion of the board.

Thanks!
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spamunkulus



Joined: Jul 02, 2012
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Location: berlin

PostPosted: Mon Jul 02, 2012 10:10 am    Post subject: Reply with quote  Mark this post and the followings unread

Is your Drumtraks working meanwhile?

When the +5Volt of the digital supply is correct, the power supply
seems not to be defective.
check the Reset Pin of the Z80.
Do you see any clocksignal on the Z80 and did you check the signals at
the address ports and the Data ports of the Z80?.
Do you see any levels between HI and LO? This is in most cases
caused by a defective input on the DATA or address , sometimes
can be the Z80 itself. You can stop the clock and check the voltages
and currents static. A bit tricky without cutting a connection on the bus or desoldering a chip. Sometimes you have to do that.
The Z80 gets 4MHZ on pin 6. Master clockgenerator is U212Pin8 (8MHz).
Divider is U221/7493

I try to scan the schematics soon and put it on elektrotanya.com + PM
As well I am looking for a schematic of the simmons SDS8 and the DYNACORD EC280 Delay.

Good luck

Tito
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defog



Joined: Aug 24, 2011
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Location: Philadelphia

PostPosted: Mon Jul 02, 2012 11:23 am    Post subject: Reply with quote  Mark this post and the followings unread

SOLVED - The main issue was a couple of bad tantalum caps and two faulty voltage regulators on the power supply as far as I could tell, and a bit of ripple from the older filter caps. I replaced all the filter caps, tantalums, and the two bad regulators. But for whatever reason, the modern 7805 I replaced the original with wasn't playing nicely, and the voltage output was off. That's the part I couldn't figure out for a while. As soon as I replaced the 7805 with an older version I grabbed at the rat shack, it booted up, all voltages looked great, almost no ripple on the scope.

Next issue was a few switching functions were misbehaving. Typical of logic ICs of this era. Traced it back to a few 4051s, socketed them and replaced them (4 total I believe).

THEN there's more! A bad CEM VCA on the kick channel. $60 and it is working again. Total time to debug = about 5 hrs. Total parts cost = $90. Not too bad. Certainly would have been easier to debug the logic part with the schematic, and the voltage regulator anomaly was just flat out odd.

Now I just need to finish up that damn obx-a that has been sitting on my bench for the last 8 months.

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spamunkulus



Joined: Jul 02, 2012
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Location: berlin

PostPosted: Mon Jul 02, 2012 12:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

Uhh, I have never seen a DrumTraks with that many bad components!
Nice, that you got it back to life.
cheers, Tito
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defog



Joined: Aug 24, 2011
Posts: 113
Location: Philadelphia

PostPosted: Tue Jul 03, 2012 7:16 am    Post subject: Reply with quote  Mark this post and the followings unread

This is the first one I've worked on, but from experience with a lot of other gear, I agree, way too many things went wrong on it. I'm guessing the switching stuff was there prior to the power supply going bad. The reason for the death of the PSU was due to my Father in law not turning it on for like 10 years and the caps being dried out. The CEM failure doesn't surprise me though, I've replaced at least a dozen of them in a short time I've been repairing 80's era gear.
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spamunkulus



Joined: Jul 02, 2012
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Location: berlin

PostPosted: Wed Jul 04, 2012 4:13 pm    Post subject: schematic SCI Drumtraks Reply with quote  Mark this post and the followings unread

Ok, I finally scanned the dog-eared papers and did some makup.

schematic of the sequential-circuits inc. DrumTraks is on
elektrotanya.com now. Use the search funktion or:

http://elektrotanya.com/sequential_drumtraks_sch.pdf/download.html


Cheers,

Titone
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JingleJoe



Joined: Nov 10, 2011
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PostPosted: Thu Jul 05, 2012 1:40 am    Post subject: Reply with quote  Mark this post and the followings unread

I'm getting: file not found Sad
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elmegil



Joined: Mar 20, 2012
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Location: Chicago
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PostPosted: Thu Jul 05, 2012 3:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

Search found me this, which appears to work on my end:

http://elektrotanya.com/drumtraks_sequential_circuits_inc_sd400-i_sch.pdf/download.html
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spamunkulus



Joined: Jul 02, 2012
Posts: 6
Location: berlin

PostPosted: Fri Jul 06, 2012 9:46 am    Post subject: Reply with quote  Mark this post and the followings unread

correct, that is my scan of the drumtraks.

Anyway, if it moves inside www.elektrotanya.com, use the search funktion.

Tito
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Anarchia



Joined: Jun 04, 2007
Posts: 4
Location: Minneapolis

PostPosted: Sat Nov 03, 2012 8:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

@ spamunkulus

Thank You! Thank You! Thank You! Thank You! Thank You! Thank You! Thank You! Thank You! Thank You! Thank You! Thank You! Thank You!

I've been looking for these schematics for several years now. So again, Thank You! Very Happy
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spamunkulus



Joined: Jul 02, 2012
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Location: berlin

PostPosted: Sun Nov 04, 2012 2:41 pm    Post subject: Reply with quote  Mark this post and the followings unread

I am pleased that scanning the document
was no waste of time, and extrapleased to help out anarchia.

cheers, spamunkulus
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Anarchia



Joined: Jun 04, 2007
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PostPosted: Sun Nov 11, 2012 7:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

And just so you know, 2 hours after I downloaded the schemo I had a major LED malfunctioning issue resolved. 5 years of flying this beast blind, now I can finally see what I'm doing. Thank you! Thank you! I should point out that this drum machine is intuitive enough to where it's possible to operate without the use of a functioning display. Thank You! Also, Hi-Res scanning of just about any Service Manual is never a waste of time. The more access we all have to documentation the longer our beloved noise toys will be around to make the noises that made us fall in love with them. Thank You! Thank You!
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asfi



Joined: Apr 01, 2013
Posts: 1
Location: Toronto

PostPosted: Mon Apr 01, 2013 2:21 pm    Post subject: Found: the service manual! Reply with quote  Mark this post and the followings unread

I was pleasantly surprised to find this, and first search result to boot!

http://www.cem3374.com/docs/Manuals/Sequential/Drumtraks_SM.pdf

Alas, it's been ages since CPU circuits have been so straightforward. Crying or Very sad
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