Yamaha SPX 90, 1986 , Digital Multi Effects Processor

Millions of them made, superseded by the SPX 900. All the programs within also contained in the much more capable REV-7.

The 90's and many other Yamaha devices of the mid-80's suffered from a potting compound which often turns conductive with age....

jak

necessary

Cold checking , have found 2 things wrong with the ps so not powered up yet No SMPS controller IC on the ps board , a TOP66 switcher driver and 3 small transistors. Raw + and -18V go to main board +/-15V regulators , raw 5V , ie rectifier off the switching transformer followed by one L and one C goes straight to the 5V TTL rail. Not even an obvious fat 5V zener across it. No SMPS controller IC , that I can see on the main board and the 2 lines from the main board marked PE and PC that go to the mains side of the ps via opto isolator , I'm assuming is go / no-go for the moment.

5V regulation via the whole ps unit ? very strange

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

state.

day

yet

small

via

There are 15 assorted wirewound resistors on this ps , again rather odd. If I get it working , a ventillation hole and grill cut in the top cover would help.

Shouldn't be needed, those things get racked up in close proximity to other units for years without overheating, they are normally considered extremely reliable even when running 24/7.

Although considered a 'classic' in it`s day, there are several modern units which outperform the SPX90 at a far lower price.

If you really get stuck and it`s imperative that it gets repaired, drop me a line, I know of a company up here in the North who will definitely sort it out.

Ron(UK)

--
Lune Valley Audio
Public Address Systems
Hire Sales Maintenance
www.lunevalleyaudio.com

It was that hand over period , 80s , when phenolic pcbs went over to polyester. This Yamaha has polyester main board and phenolic light brown ps pcb that has a lot of heat dark browned/brittlised? areas. Not surprising with assorted 15 W/W plus sm driver etc with no ventilation holes anywhere.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

rectifier

to

lines

ps

Got it back to working to its earlier non-working condition before it was seriously mangled by a "repairman". Can now see that the original problem was an 85 dec C electro that did not like being cooked in there. The 5V regulation, unlike the +/-15V, is on the ps itself, in discrete form, consisting of 300mW zener,preset and TO92 transistor.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

Hopefully get back to this one tomorrow. Working at 2/3 mains coltage but temp of the chopper transistor goes too high, if I let it, and power consumption goes well above 20W. Looks as though something has gone wrong with the mark/space contol. It slowly increases so the "5V" line goes 2..3V and then jumps to 5V with equal mark/space which is presumably not necessary. I will check there is no excessive load on the +/-18V or 5V rails despite all functions working as far as front panel display. I've not established the function of the feed forward optocoupler from the main processor board to mains side of the ps

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

The second optocoupler is the other way round. Feeding rectified but unsmoothed mains signal info to the main board. Phase info for mains hum/noise reduction?

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

I think I've cracked it, one of the most awkward of repair situations. A previous er-um repairman had got there before me. I can only assume that the previous one noticed a component populating a pair of holes , on traces, with no corresponding overlay graphic outline or designation and removed it as suspicious. Numerous such holes, unused for this model, on the pcb . I assumed, from the disturbed solder , that he'd tried something temporary at that point but it looks as though there was originally a small C there that slowed down the HV response to the LV error amp via opto coupler. The optimum error V was about 5 minus 2.2V but it was racing over that up to

5V, as there was no capacitance in the error amp, so cutting off the OC and forcing the HV oscillator to maximum power consumption and all error control lost. Now just a matter of finding the optimium, educated guess/suck it and see, for that C, 100nF works but going by pin spacing must be less than that.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on