Macrohenry,
I'm not much with ICs and have never worked with SMDs. I am attaching a pic of the one I bought and could you tell me which components need "shorting'?
Thanks

I see input and output pins on the left. The chip caps corresponding to them (adjacent to and in line with the pins) are likely connected to the respective pins, but you'll have to check. If so, just short the input and output caps. Makes sense?

Then check to see that you indeed have a DC amplifier by connecting a 1K, 10K, or even a 50K pot to a 1.5 V battery so that each outer terminal of the pot is connected to the positive and negative of the battery. Check the pot setup by measuring the voltage between the wiper and negative terminal as you turn the pot. You should get 0-1.5 volts.

Now, set the pot to 0 volts or close to it. Connect the wiper to the input of your modified board, connect the negative terminal to the board GND, connect your voltmeter to board output, now power up your board.

Slowly advance the pot, watching the meter for a rising DC voltage. At 100X gain, you'll quickly run out of headroom. You just want to see if you have a rising DC voltage before you connect it to the meter.

Instead of a pot you can connect a 100K resistor in series with a 1K resistor, use the common connection for the wiper, connect GND to the 1K and the battery positive to the 100K. The "wiper" connection will give you approximately 1/100 of 1.5 volts. So the output of the amplifier should be about 1.5 V. Then check with a 3 volt battery. Don't use a battery that gets close to or exceeds the power supply voltage.

Macrohenry,
They finally arrived, long story.
Anyway in looking at the specs I presume it is cap C3 and C4 that I have to short out? I am showing the diagram and a picture of the items I plan to short.
Thanks, without filaments, I am lost!
Thanks,
Carl

I am working on projects building a VTVM.
The chip I am is down to 50pA.
Simple to use.

Dave

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Yes, those caps block DC. Looking at the board I thought there was a cap on the output of the second op amp. If so, it would need to be shorted, too. Might have to examine all the traces and reverse engineer it to make sure.

Where did the schematic come from?

The schematic came from a TI spec sheet. All the parts in the schematic are accounted for and I don't see a blocking cap on the output so I should be good to go.
I really appreciate the guidance.

You may want to start with a digital meter before you accidentally peg your micro amp meter .

I edited my post to say "shorted" not "blocked. " But I see you got it anyway.

+1 per Mark's suggestion on trying with digital voltmeter first.

The traces are all covered> assume it is a sandwich board of some sort. I had originally planned on putting a small piece of wire on the trace but can't get to it. So I will remove the caps and short them.

Agree on the multi-meter.
Tnx

Hi gents,
I think the current plan won't work the way you want it to. Shorting the capacitors is necessary to allow the DC part of the signal of interest to pass through but in this circuit there is more to consider. This circuit is meant for use with a single polarity supply and as such biases the opamp to operate with a fixed voltage offset between 0 volts (ground) and the supply volts. The board's output will be roughly 1/2 the opamp's supply voltage (with the signal of interest imposed upon it). So, if your new board is conneced to a 12 volt supply, for instance, the board's output will be about 6 volts above ground and your meter will behave just the same as if you connected it across a 6 volt battery. It'll draw much more than 20uA and will pin at maximum deflection. Could damage the meter.

Also, once C4 is shorted, the gain pot between the two opamps will become a voltage divider that further affects the 2nd opamp's output offset. Current flow through the pot's wiper will make it noisy when turned, and the opamp's output offset will rise and fall as the pot is adjusted. Also, when C3 is shorted, the board's input can become a source of current backwards into the radio. The current flow is limited by the 10kOhm resistor in series with the first opamp's - input, so it shouldn't damage anything but it may bias the detector diode enough to interfere. I don't have crystal radio experience (other than an oatmeal tube thing we built in the 6th grade), so I'm not sure how much of a problem this would be.

The same opamp with a bipolar supply and altered circuit could do the job better. Or, another opamp to create a virtual ground for the other leg of the meter could be another approach, but a bit more complicated still. I can draw a new circuit if you wish. It might be possible to use the same board by removing a few resistors and cutting a couple traces, if that is a practical idea.

The caps can be shorted without removing them or digging for traces. Tack solder a strand across between the two ends of the part. Do one side at a time and the cap won't float away. Easy to cut or remove later on.

This out of the ALLR Book.
It used on a FET voltmeter aka VTVM
Uses a LF353 chip