Big transformer, linear regulators, two-sided board, bunch of DIPs.
Looks like the power switch is on the left at the back, and they've routed some long piece of metal around the regulator heatsinks all the way to the front panel. Anyone know why they'd do that?
The ICs seem scattered all over with not a lot of rhyme or reason to their positioning - make room for all the jumpers?
The power switch controls the mains directly- to run traces to the front would require a lot of space on the board. Or they'd have to run thick wires insulated to the satisfaction of every safety agency in the world where they wanted to sell units.
It's cheaper and better to put all the mains-connected stuff together, near the power entry and operate the power switch with a button extender. IIRC my old Tek scope has something similar.
It's a single-sided paper-based phenolic board- and it looks like they've laid out an 8-bit microprocessor (maybe a Z80 or 8051 variant?) with external EPROM and RAM.. so yeah there are a lot of interconnections in the digital part of the circuit and few components to use as jumpers- looks like it was a massive PITA to lay out.
That fashion of "paper-based phenolic" board seemed very common in "prosumer" equipment from Japan in the 1980s, right up until around 1990 when it seems everyone made the jump to double-sided FR4.
The service manual shows it using the somewhat obscure (to me) "63803X" uP, plus an "XB 186002" 64kbit ROM chip, and a "TC5544PL" 8kbit RAM chip, to scan the front panel and MIDI and drive the 4 op FM chip (YM2414.)
IIRC the innards my Yamaha pf-70 look about the same. Its microprocessor will be noted the next time it's opened.
One of these days, real soon now, a half dozen of its biggest 'lytic caps will get replaced. ... hmmmm ... hold up ...
.. goes out to look at the brand name on the replacement 'lytics in the parts drawer ... Lelon ... out of Twaiwan?!?! ... the land of the capacitor plague?!?! [1] No fricken way!
My beloved pf-70 was this close ][ to getting pathogenic transplants. It's time to throw out those Lelons and replace them with Fujitsu, Nichicon, Oscon, Rubycon, Samxon, or UCC. What other brands does the group find trustworthy?
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Thank you,
--
Don Kuenz KB7RPU
The key to the mystery of a great artist: that for reasons unknown to
him or to anyone else, he will give away his energies and his life just
to make sure that one note follows another inevitably. ... The composer,
by doing this, leaves us at the finish with the feeling that something
is right in the world, that something checks throughout, something that
follows its own laws consistently, something we can trust, that will
never let us down. - Leonard Bernstein
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Tim Wescott
Control systems, embedded software and circuit design
I'm looking for work! See my website if you're interested
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Historically Roland seemed to prefer Intel-derived processors in its products (8051 etc.), Korg and Yamaha liked Motorola/Hitachi, while the US manufacturers (E-mu, Oberheim) liked Zilog/MOSTek.
You could make a two-layer board in your EDA tool, choose "vias" big enough to solder wires into, and then lay it out by hand with the understanding that you're really just putting in jumper wires.
I've never done it, but it'd probably speed things up.
This sort of product lets you flog the engineering because you'll make so damned many of them.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
I'm looking for work -- see my website!
I think he's referring to the mechanical link from the button on the front panel to the switch behind the heat sink -- it's the sorta-silvery gray thing at the far left, kind of sneaking around the heat sink.
But yes, the bar about 1/4 of the way to the right is a mechanical support.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
I'm looking for work -- see my website!
LEDs are common now, too, as long as they're blue. I was really hoping that the "stick a blue LED on it so it'll be MODERN!" thing would be a flash in the pan, but it's been a decade, and consumer devices with blue LEDs are still not seen as being charmingly dated.
--
Tim Wescott
Control systems, embedded software and circuit design
I'm looking for work! See my website if you're interested
http://www.wescottdesign.com
My memory's wrong this time. The pf-70 uses a double sided FR4 PCB. All components are through hole. (It's several decades old.) It also uses an HD6303RP MPU.
So the board that looked like the TX81Z was in my bone pile within the past year. It probably came out of a failed printer or scanner that was manufactured during the past ten years.
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