Hello WimWalther,
Hi WimWalther,
So where are you now in the repair process ? Do you need some additional help ?
I reinstalled the modulator board, but it's still not working. I'd done a bunch of cleanup of the pcb work, it was substandard. One issue is that I still don't know how & when the modulator effect should operate.
Sure than if the PCB isn't reliable, it might create additional flaws.
Q1) Could you validate that all of the stuff on the top left corner works fine ?
Sorry, which stuff? Do you mean the channel switching circuits in upper left of the schematic? Best as I can tell, they aren't even present in the TE model. There's only one footswitch jack and it controls speed & on/off for the modulator.
Yes, I was speaking about the 'channel switching' and 'reverb recovery amp' stuff.
But if those features are not present/implemened in your device, this simplifies the schematics.
At one point, some input signal should arrive at U6A (full left in the middle) and then head towards U7.
As far as possible, try to track the input signal at this location (around Q6).
Q2) When you feed an input with 1kHz sine 5 mV peak to peak, and using an oscilloscope, do you catch some signal at U7/pin 5 ? And U7/pin 8 ?
In the negative, give a second try with 50 mV peak to peak.
Q3) The PNP transistor 'Q7' seems to act as a current source. Can you measure its' DC voltage at the base pin ?
This will all require testing. I'll perform it as I'm able - I'm disabled, everything takes like 5x the time & effort it should.
So sorry to hear about your predicament. Take as much time you need. Nobody's in a hurry.
Btw, I was also wondering about Q7.. and why R96/97 are dashed-out, almost as if they are optional parts. But you're likely right it's CS, as else I can't see how Q8 is biased linear.
I would say that the dotted parts are just a scan artefact and as oPossum underscored, those parts are required.
The vertical line just above (which links R63, R60, R61) shows the same printing failure.
Q7/R96/R97 is a simple current source that is used instead of the 47k resistor shown in the datasheet.
Datasheet.. you mean schematic? So you're saying that R98 (47K) is deleted? Why do you think that?
I guess that oPossum was talking about 'RL' (47k) that is shown in the
TDA1022 datasheet at page 6 & 7.
So.. backing up.. does anyone know what the purpose of this block is? (Attached). It's like some sort of bridge, with the 4 diodes and mirrored resistor values. Though, there's dissimilarity in the 220R / 270R pair that grounds it.
Reminds me of an FM detector.
Not a bad idea, because an RF (AM/FM) detector extracts a baseband (demodulated) signal from another more complex (modulated) signal.
So I have another close guess : the weird resistor and diode ladder makes me think about a
kind of sine converter.
I wanted also to figure out what the function of U9A & U9B is. It seems to be a relaxation oscillator so the waveform at U9B/pin7 should be a
periodic exponential signal (charge and discharge voltage of a capacitor).
So the block you mentioned could be an 'exponential to sine converter'. But other suggestions are welcome.
For such uncommon schematics, a certain answer is not obvious and
in situ measurment and/or spice simulation is not a luxury to confirm the analysis.