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I am repairing a vintage Seeburg/Gulbransen 'Select-a-Rhythm' drum machine from 1967, the kind you would sit on top of your organ and play along with.

I am trying to distinguish what this component could be, it basically looks like an old capacitor but it has 7 legs. I've attached a photo below to identify it (highlighted in yellow circle):

enter image description here

The item states SPRAGUE 663044-4, it has 7 feet and there are 6 of them. could these be the pulse generators(for the rhythms) or some kind of logic circuit? The schematic diagram states them as PC001, PC002, etc. The circuit diagram is attached below also. Could PC stand for Pulse Circuit?

enter image description here

Also, if anyone can identify the mysterious transistors which all say '4000' on them and nothing else. the schematic states them as 'q2001, q2002, etc)

The machine didn't turn on when I first bought it and now I have it lighting up, I've attached a foot switch to start/stop the rhythms which is working perfectly with the tempo light, but still no sound!

I've re-capped all the old paper and film capacitors so I'm hoping it could be a few resistors somewhere because these mysterious 7 legged creatures look like they could be difficult to find replacements.

Thank you for your help, I'd love to hear this thing working once again! This is just a hobby for me so I'm in no rush, looking forward to your reply.

Here is a link to the full service manual if needed.

yuritsuki
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Rex Rick
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2 Answers2

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Those are small PCBs with a passive filter network in a single inline pin package potted with epoxy. The schematic on the far left within the dashed lines shows the components of a single board (notice, the pin-out for that part of the circuit is labeled 1-7), and it is not drawn for the others (presumably identical) to save space. You can replace them with what is inside the dashed line on the left side of the schematic, but it is unlikely to be what is broken, since everything inside is a passive (just caps and resistors).

Here is the schematic for each module, from the original schematic

Zuofu
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    ah ! my dyslexic eyes ! spent so long looking and didn't even see that blown up explanation on the side. could it possibly be one of these strange 4000 transistors? thank you ! – Rex Rick Nov 09 '15 at 01:37
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    What's in the module (PCxxx) appears to only be the passives, the transistors are external to the module, and probably on either side of the module on the PCB. I can't identify any 4000 transistors, but you can try replacing with any generic NPN (2N3904 or 2N2222)...the circuit doesn't seem like it would be very sensitive to the type of transistor. – Zuofu Nov 09 '15 at 01:44
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    Caps can blow, the circled one does have a large bump in it. – Alec Teal Nov 09 '15 at 18:14
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Any jellybean NPN transistor (2N2222, 2N3904, etc.) should work fine in this circuit.

The manual is quite detailed in describing exactly what each circuit does. As Zuofu said, the 7-legged orange squares contain the passive circuitry shown inside the dashed line in the schematic diagram excerpt you show. One of these and a pair of transistors constitute one of the six flip-flops in the 48-step counter.

If you're seeing the tempo light, then much of the logic part of the unit is working, so you need to focus on the parts that generate the sounds and buffer them to the output jack. Since you're getting no sound at all, start at the end and work your way backward into the circuit.

Do you have an oscilloscope? It would be extremely useful to have one to debug this unit. Even a cheap soundcard-based one would do for this project.

Dave Tweed
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    i think i've just located the blown up version of the 4000 transistor in the service manual. (section 1, pages 11-12) let me see if i can attach it here.. makes sense now. – Rex Rick Nov 09 '15 at 02:47