Yamaha E1010 rack delay

[J M Fahey]

When I was young (do the math ) tantalum caps were the new space age advanced components and using them was a sign of distinction.
In fact they are still much used in Aerospace and similar level stuff ... but I guess they pay extra and get "the good ones".
5/10 years passed and problems started to appear, so much so that aluminum electrolytics regained their place.
I *guess* they are very very sensitive to internal chemistry or something, because they are still around, although in the expensive bracket.

[m1989jmp]

Yamaha's service manual states that the clock frequency should be 27.3kHz which corresponds to 36.63us clock period. Rotating the VR3 to both extremes I can get only 8-10us range.

I don't quite understand how clock is set with BA617 IC, so my question is what could've caused such a radical shift in clock frequency?

[g1]

DC voltage on pin1 and 2, as well as capacitor at pin3, sets frequency. So DC could be out of range, due to some problem further upstream (maybe IC10 or TR23), or a bad cap at pin 3 or 4.
see pg. 133 or 134 of pdf link for info on BA617 chip.

http://goltsynth.com/resources/downl..._guidebook.pdf

[m1989jmp]

DC voltage on pin1 and 2, as well as capacitor at pin3, sets frequency. So DC could be out of range, due to some problem further upstream (maybe IC10 or TR23), or a bad cap at pin 3 or 4.
see pg. 133 or 134 of pdf link for info on BA617 chip.

http://goltsynth.com/resources/downl..._guidebook.pdf

Looks like they made a mistake in service manual, because a graph to the right of the schematic shows that with DELAY control on LONG, clock should be 27.3kHz. I can get that value with trimpot although it gets extremely jerky at that point.

However, with DELAY set to SHORT I'm back at around 10ms clock period with pot maxed, so I'll definitely check those caps.

The only other problem I've encountered is with 10ms delay setting. It produces a sound with a nasty, gating-like distortion that looks like a sawtooth wave at the wiper of VR8. I've narrowed it down to this area:



The signal is fine up to pin 3 of IC19, but gets scrambled at pins 13 and 14:





For comparison, I've attached pics from the output of IC11 that works fine:

[m1989jmp]

I've tried swapping LPF sections between 10ms and 75ms sections just to confirm the problem is with IC19. IC11 and IC19 share same clock signal so I'm certain that's not the issue here as IC11 works nicely.



I'm now left with a dilemma that either whole MN3004 (IC19) doesn't work right or it's biased way off. Voltages on IC19 are as follows:

PIN:
1 0V
2 -7.5V
3 -6.7V (bias voltage)
4, 5, 6, 7 -13.86V
8, 9, 10, 11 -15V
12 -8.33V
13 -6.83V
14 -6.89V

I'll now try biasing it with external voltage source and if that doesn't work just order a replacement MN3004.

Any suggestions are welcome.

Edit: both MN3004 and MN3005 datasheets state that bias voltage is set from -5VDC to -10VDC. For comparison, I've set first MN3005's bias voltage at near -9VDC following info in the service manual.

[m1989jmp]

Setting IC19 bias from outside did the trick, there's a clean signal now on the VR8 wiper. After looking more carefully at the schematic, I see an asterisk near resistor values that make up voltage divider that sets bias voltage, but don't see a reference anywhere...



Either way, if changing that cap going to ground from there doesn't raise voltage sufficiently, I'll experiment with a pot there and work out voltage divider resistor values.

I wonder why they didn't put a trimpot there too.

[g1]

if changing that cap going to ground from there doesn't raise voltage sufficiently, I'll experiment with a pot there and work out voltage divider resistor values.

Both caps there should be checked, the one parallel with the 4k7, and the one coming off pin4. I guess the coupling cap there into pin3 could also throw off the DC if it is leaky. So three caps total.

[m1989jmp]

Both caps there should be checked, the one parallel with the 4k7, and the one coming off pin4. I guess the coupling cap there into pin3 could also throw off the DC if it is leaky. So three caps total.

Thanks for suggesting that, already pulled those and all tested fine. I'm getting a clean signal now since replacing that 5.1k resistor with trimpot set up as a variable resistor so it should be fine now.

The last issue I'm having is regarding that modulation waveform. Service manual information is a bit conflicting; the schematic shows 2.5V peak to peak, 100ms period sawtooth wave on the DEPTH control wiper (with DEPTH and FREQUENCY controls maxed out):



However, a paragraph just before the schematic states that with all controls except FEEDBACK maxed, the waveform on LFO pad/point (which is the same thing as the DEPTH control wiper) should be 15Hz or 66ms period and again 2.5V ptp:



When measuring, I get around 65-70ms period with correct amplitude but I can't increase period any further with VR4 without distorting tips of the waveform. Obviously, that's fine according to that paragraph, but wrong according to schematic.

Am I missing something here or they made an error?

[m1989jmp]

Also, am I right in converting -20dBm to 219mV using this calculator for 600Ohm impedance? I've used 219mV for -20dBm and 292mV for -17.5dBm, but it seems to me that wet signal is louder than dry when MIXER control is set mid way.



https://www.random-science-tools.com...atts-volts.htm

[m1989jmp]

After a bit of tinkering, the unit now works flawlessly except for LFO. Following the manual, I've set the LFO frequency to 15Hz with DEPTH and FREQUENCY controls maxed.

However, when I try to go below 8Hz (7 on the FREQUENCY knob) the LFO wave disappears and all I'm left with is negative DC voltage on the scope. In addition to that, the LFO's peak-to-peak voltage can't go past 2V and the manual states 2.5V. So, basically, the modulation doesn't work with FREQUENCY set below 7.



I again see those damned tantalum caps (marked with a triangle) in the 4558 OPamp's feedback loop, is it possible they're giving me a headache again?

[m1989jmp]

Well, these tantalum caps certainly have weird failure modes; both were shown as diodes with nominal (!) capacitance when tested with a component tester.

All is fine now in the LFO land.

[g1]

I've run into a few units where you have several tantalum failures like that and you just have to go through and replace them all. This may be one of those.
There was an era where the failure rate for tantalums was quite high.

[m1989jmp]

I've run into a few units where you have several tantalum failures like that and you just have to go through and replace them all. This may be one of those.
There was an era where the failure rate for tantalums was quite high.

Do you think it's better to replace them with high quality electrolytic or go with tantalum again?

[g1]

I think a modern high quality electrolytic.

[Emmanuel Hubaut]

Hello I just bought a Yamaha E1010. I have a basic question is it normal that the output level is lower when Mixing knob is at Noon ...and much higher in direct or full delay position ? The difference is quiet big few Db ...this is happening on the rear output, and the front output in the same way ...one other thing is my front output is lower (few db) than the rear output ...I think they should be identical ? Thanks for your help ...