Crate SFX-212t DSP Effects Are Not Working

[crl]

So I reconnected some wires today and got the amp working again, however the DSP effects are not working. Everything seems to be connected correctly and here are some pics to prove it. Schematics can be found (the 7th post down) in the schematics forum here https://music-electronics-forum.com/...ad.php?t=20270

I have the amp sitting on top of the cab where it is open for messing with and have tried wiggling the harnesses going to the DSP board (or what I think the DSP board must be anyway). It didn't make the DSP effects come on.



https://ibb.co/wNqKktN

[DrGonz78]

Good thing is that there is schematics for the dsp for the amp. It's a bit complex though. First thing is to check for +5vdc supply on the dsp board. Do you have a multimeter to check voltages on the amp?

[crl]

Yes, I have a multimeter. I've tried checking for 5v between the spot (which I think is a testpoint) next to D1 (with the positive probe) and the spot next to R36 (which should be a ground with the negative probe). I checked 3 times and didn't get anything (however I don't have a magnifying glass and the components are smaller than small, so it's hard to know if I had contact).

After that, I put the +probe on the D1 lead on the 'wall' side and the -probe on the R36 lead and got a little over 1V.

I am guessing on how to do this, because I'm not really too sure. I have some experience with auto electronic troubleshooting, but nothing this complex.

[crl]

In addition, I've now tested the grey 4 wire ribbon cable marked J4 between with -probe in wire 2 and +probe on wire 3 and got something around negative 1.28V.

I'm confused about the schematic though, because the only harnesses going to the soundboard are marked J4, J10, and J12, yet the DSP schematic doesn't refer to any of those, instead it refers to J1 and I think J6, depending on which grouping of 2 pages I'm looking at (ie which version of the soundboard, with each version having 2 pages).

There is another 4 wire cable that's a regular non-ribbon type (with thicker red wires). That one is J10.

[Enzo]

Each board has its own jack numbers. So look on amp drawing page 1. Bottom center see J10. That is J10 (Jack 10) on the amp board. It is the main connector to the DSP. They even made it plain as in "processed signal" (pin 1) and "unprocessed signal" (pin 2). In other words FROM and TO (the DSP card). Pin 3 is ground and pin 4 is the raw supply for the DSP. The DSP runs on regulated voltage, but that is done ON the DSP card. this is just a basic supply for that. See Tp16 there, and according to the chart on next page, Tp16 is +10vDC. So find J10 on the main board and see if around +10v is there. Ground your meter to chassis for all readings unless told otherwise.

The same DSP card is used for different models, but it has changes for them. SO which boards is yours? Last two digits?

I will refer to page 1 of the DSP stack as an example until you tell us which you have. Left center see J2. That is what connects to J10 on the main board. See the in, out, ground, and power pins? Note pins 1,2,3,4 are not the same on both, so pay attention. Pin 2 is ground and pin 1 is the +10v, aka VIN. Got 10v there? From there, see page 2 lower left. There is your simple 5v regulator. Got +5 coming out of that? it is in the corner of your DSP card.

Pin 3 of J2 is INPUT to the card and pin 4 the OUTPUT. Follow the circuits over to the big IC and see those names. If you shorted pins 3 and 4 together (or pins 1 and 2 on the main board) it would bypass the DSP, signal wise. Maybe for just a second to test.

D1 on the DSP card? Only the cathode end goes to +5v, not the R36 end. I would first look for +5 at the regulator. Easy to find. And if it ain't there it won't be anywhere else.

Once your I/O reaches the big IC U2 it enters the digital domaine and you can't trace the signal around the board.

Other connectors on the DSP would be for control inputs from panel switches or whatever.

[crl]

My DSP board ends in -12, so it must be pages 9 and 10 on the DSP schematic.

Did you see TP16 in the illustration? I can only find it listed in the table. The highest I see is TP15 in section E3. I don't know how to find where it is so can't check for 10V at that point.

Anyway, at J10 on the mainboard, testing +probe on pin 4 and -probe on chassis I have 1/3V, so I don't have 10V there.

I checked for 10V at Pin 1 on J1 and -probe on the chassis the DSP board too, and of course didn't have 10V there.

For testing the 5V regulated voltage, I see R56 on the sheet, but they didn't have space to print it on the board but I do see R54 on the board. Is there another way to identify R56 from the number printed on the resistors? Would it be close to R54?

I'm trying to figure everything else out. I'm trying to figure out a way to follow the traces. Some are on top and some on the bottom of the PCB. I'd like to know which pin is pin 1 on the AD1881 (this is assuming you meant the AD1881 chip and not one of the other 2) but I don't see an indication on the board. If I knew that, couldn't I just test the continuity between J1 pins 1 and 2 and whatever pin they lead to on the chip, or would that not tell me anything important?

[Enzo]

Perhaps I wrote poorly. TP16 is on the main board. It serves pin 4 of J10 there through that 10 ohm resistor. Do you see J10 on the drawing? TP16 is very near.

To check +5 on the DSP, just find the Voltage regulator, and measure on its leg.

I got TP16 from the illustration. TP16 is on the other page of the main schematic, bottom center. A very simple power supply. If you don't have 10v at pin 4 of J10, your DSP will not happen. Is R107 open? 10 ohms.

I don't recall mentioning R56, what was that?

Until you get 10v to the DSP board NOTHING you measure there means anything. Without proper power no circuit works.

You want to know about AD1881? Look up its data sheet. Should include a pinout. But right now it has no power, ut suts there dead, go find your 10v, THEN worry about whether the 5v regulator on the dSP works.

[Jazz P Bass]

I believe what Enzo is trying to tell you is that the +10 v supply comes from the main board.
J10.
TP 16 10Vdc.pdf
If you do not have that voltage then there is no use even looking at the DSP board.
In fact you should disconnect the DSP until you can get the +10 supply figured out.

[crl]

I didn't understand what you meant before and thought R56 was a part of it, nevermind. I don't get anything close to +10V at TP16 and still nothing at pin 4 of J10. I tested TP16 on the cathode side of D32 (The side with the silver band around it).

I also checked for continuity between the cathode side of D32 and the near side of R107, and then the far side of R107 (in which I got 10ohms), so R107 isn't open and there isn't an open somewhere along the trace.

So what's next? Do I go further back in the circuit? I'm looking at the mainboard schematic but am not sure where to go.

And Jazz P Bass, I can't completely disconnect the DSP board unless I want to desolder the ribbon cable.

[DrGonz78]

Just have to ask if J11 and J8 are plugged into the board. Excuse my question if it has already been addressed. Going back to the old thread we had two orange wires that were never used. If nothing is plugged into J11 & J8 then I would check the AC voltage of those orange wires as they might be the low voltage secondary taps. Just a thought...

[Enzo]

Well, YEAH^^^^

I must read too many threads, I never connected this thread with the loose wires thread elsewhere. If TP16 has no voltage, then yes, we go back a step and check for AC before the rectifiers.

[crl]

No, J8 and J11 are not plugged in, and they are right next to the D31-34 cluster. The XFMR is the only part with unused wires, and looking at the right side of the XFMR illustration it looks like there are 3 leads connecting to the mainboard from the XFMR, J13, J22, and J23 and those are all connected (with the green wire going to J13 and 2 red wires to the others). What is unused are the two orange wires. Since these come from the transformer, is it necessary to ground them somewhere other than the chassis? How do I check for AC on the two orange wires coming from the XFMR?

On an unrelated note, I biased the tubes on my Marshall 2 nights ago and learned what a trim pot is, there's one on here too and is shown in section D2 on the second page of the mainboard schematic. I'm interested in knowing why I would want to adjust voltage across the noted resistor.

[Enzo]

What is unused are the two orange wires. Since these come from the transformer, is it necessary to ground them somewhere other than the chassis? How do I check for AC on the two orange wires coming from the XFMR?

NO, don't ground them anywhere. Now that we have connected the two threads, they would gn the open posts we just discovered. The schematic shows our 10v supply needs them.

Measure? Put meter on AC volts and put one probe on each wire. There is no ground connection or reference.

learned what a trim pot is, there's one on here too and is shown in section D2 on the second page of the mainboard schematic.

Do you mean AP1? it is the bias adjustment for the power amp, and is set exactly as instructed on the drawing nearby.

[crl]

This was fascinating and I really enjoyed learning about it. Thanks for your help Enzo and Gonzo. You've probably guessed that the orange wires fixed it. Everything is working!