Carvin V3 - perplexed

[nickb]

Ok so what do these signals on these pins look like? I'm guessing the static voltage changes from some positive voltage to 0v, or vice versa, when a channel switch is thrown? Therefore turning the transistors on/off that control the relay coils. I get that when a positive voltage is applied to the transistor base, the transistor saturates therefore pulling current through the relay coil.

The outputs of the 595's will be as you say. The clock and data inputs to the them will be a pulse stream. The LCLK input will have a pulse once each time the micro sends out an update to the 595's.

[lowell]

Ok so I checked for the TR signals on U2 outputs. I don't see anything on my meter. The amp is "stuck" on channel 1. I monitored mv on TR1-2 and TR3 and only see 6mv. This does not change when I toggle the front panel momentaries. It was suggested that I look for the switching signal earlier in the circuit. I have my scope on .1mv/1mS and don't see anything on the clock pins when I toggle the channel switches. What would this signal look like on a scope? Being that there is absolutely no sign of life on those pins I'm thinking that U1 is the problem.

EDIT: I'm an idiot. I had the amp in standby haha.

Ok so the SCLK pin2 does put out signal when I toggle the channel switches. The LCLK pin3 does not change state when the switches are toggled. Also of note, again, is that when the SCLK pin2 is touched with my meter or the scope, I hear at least one relay switch and the channels switch. So either U1 or U2 is bad. How do I know which one is the culprit?

[nickb]

Sounds like SCLK signal levels or timing might be off. Measure the exact levels.

The LRCK may be wired but not used. What is the level? If it is used, it will likely be a tiny short and infrequent pulse that you will (a) need to trigger in normal mode on it and (2) will need DSO to see it anyway.

[lowell]

I don't see anything in the datasheet explaining how to use the MR reset pin. Do I short it to ground and make it zero volts? Will this not potentailly cause damage elsewhere in the amp?

[lowell]

Also getting 5v of pulsated DC on SCLK at about 40-50uS. This goes away when the channel switches are engaged.

[Jazz P Bass]

I don't see anything in the datasheet explaining how to use the MR reset pin. Do I short it to ground and make it zero volts? Will this not potentailly cause damage elsewhere in the amp?

From the datasheet, the line over MR means Reset Not. It is active Low.
Seeing that the pin is tied to +5Vdc, I wouldn't 'short it' to ground.

[lowell]

Ok let me rephrase haha. How do I reset it?

[nickb]

Also getting 5v of pulsated DC on SCLK at about 40-50uS. This goes away when the channel switches are engaged.

If your are getting signal like that I'd bet the micro is doing it's thing OK. Therefore I'd stop worrying about reset.

U2 and U7 form a 16 bit serial in parallel out shift register. What happens is the micro sends a burst of sixteen data bits to U2 pin 14, the data input. Each time the clock on pin 11 goes from low to high the data in the register get moved on to the next register with the first register in the chain taking on whatever level is on the U2 pin 14. Once all sixteen bits are shifted into place, LRCK is pulsed to copy the data to the output register and hence the pins.

You said that when you touched SCLK things started to happen. This is likely a clue. Check the low and high levels on the data in (u2 pin 24) SCLK and LRCK. To see LRCK make sure you are set the scope to trigger on it and that your scope timebase is in normal mode. If you have a digital scope it will be easy to do. If it is analog turn the brightness up and use a shade over the screen to see the very dim trace. I don't know if LRCK is there all the time or just when you press a button. You'll have to try and see.

[lowell]

Would you mind guiding me through using my scope for this? Here's my scope.

[lowell]

Sorry what I'm asking is, how to "trigger" the way you suggest. How do I connect the probe/s and what settings on my scope do I want? Thanks!

[Jazz P Bass]

Most scopes have a 'trigger' function.
It will not show a trace until something happens.
You can select to trigger on a rising edge or a falling edge.

I usually have to mess with mine until I get it set right.

[lowell]

Ok thanks I'll play around with it.
That's neat. So...on trigger, if theres say 5vdc...there'll be nothing displayed? And if this 5vdc should then have some AC riding on top of that applied to it...the trace will then appear?

Meantime, Nickb, I appreciate any elaborating on how exactly to do this....if you don't mind.

[nickb]

Ok thanks I'll play around with it.
That's neat. So...on trigger, if theres say 5vdc...there'll be nothing displayed? And if this 5vdc should then have some AC riding on top of that applied to it...the trace will then appear?

Meantime, Nickb, I appreciate any elaborating on how exactly to do this....if you don't mind.

Had guests this week so been AFC...

Set 'coupling' to NORM
'Source' to CH1
Connect CH1 to the signal of interest
Adjust 'trig level' to get the scope to trigger as you use the amp's channel switch
You can try either +ve or -ve slope as required

You'll probably have a hard time seeing the trace on that particular scope.

My guess is the levels on the data, SCLK ot LRCK are wrong. Either because of the micro or one of more of the 595's has gone bad. It would not so any harm to check you have power on the 595's too.

[Jazz P Bass]

Ok thanks I'll play around with it.
That's neat. So...on trigger, if theres say 5vdc...there'll be nothing displayed? And if this 5vdc should then have some AC riding on top of that applied to it...the trace will then appear?.

It is not only the "AC" that triggers the scope.

Any change in the signal will trigger it.

This is useful for observing a rising or falling signal.

Note: If what Nickb says is true (hard to see the signal, because of speed or short duration), then you will require a 'memory' scope.

[lowell]

My guess is the levels on the data, SCLK ot LRCK are wrong. Either because of the micro or one of more of the 595's has gone bad. It would not so any harm to check you have power on the 595's too.

The 595s have +5v on Vcc. I see pulsating DC on the SCLK which goes away when the channel switches are toggled. LCLK however has nothing, or I see nothing on the scope at all.

I guess we're at a point where we're trying to narrow it down to the 595s or the Micro. Do my results help?