Old-timey design from not too long ago

The Yamaha TX81Z, circa 1986:

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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?

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bitrex
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A horror of having any chance of mains voltage appearing on the front panel, maybe?

Other manufacturers of the era seem to have had no problem using a power switch that switches the main directly - so long as it's on the back...

Reply to
bitrex

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.

--sp

--
Best regards,  
Spehro Pefhany
Reply to
Spehro Pefhany

Oops, yeah, I meant single-sided...;-)

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.

Reply to
bitrex

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.)

Here's the underside if you're curious:

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Reply to
bitrex

Oops, it's "63B03." I guess it's a 6809 variant. Hi tek!

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bitrex

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,

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Don Kuenz KB7RPU 

The key to the mystery of a great artist: that for reasons unknown to 
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Reply to
Don Kuenz

One sided board.

The long bar looks plastic.

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Tim Wescott 
Control systems, embedded software and circuit design 
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Tim Wescott

Yep. As Spehro said, the routing does look like quite a PITA:

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Wonder if they used some early "tool assist" to help with that, or if it was all done by brain...

Reply to
bitrex

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.

Reply to
bitrex

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.

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Tim Wescott 
Wescott Design Services 
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Reply to
Tim Wescott

Long bars screwed to large boards are for mechanical support. They can also serve as partial barriers or screens.

Automated track placement would have been used in a large company in 86. It goes back longer than that.

NT

Reply to
tabbypurr

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.

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Tim Wescott 
Wescott Design Services 
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Tim Wescott

I think (from memory) it's the ROM-less version of the 6305, which was Hitachi's licensed (but vastly improved) CHMOS version of the Motorola

6805.

--sp

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Best regards,  
Spehro Pefhany
Reply to
Spehro Pefhany

Ah, I didn't see that, page didn't render well. Extension bars on mains switches were common then. And LEDs.

NT

Reply to
tabbypurr

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.

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Tim Wescott 
Control systems, embedded software and circuit design 
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Tim Wescott

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.

Thank you,

--
Don Kuenz KB7RPU
Reply to
Don Kuenz

Red, yellow, and green remind people of traffic lights - and nobody likes traffic lights!

I notice a lot of stuff uses off-white indicator lights now; I think we really want to go back to incandescent lamps.

Reply to
bitrex

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