All things G1176 - the new "repost" thread.

[btproductionsaustralia]

Great, i'll try that ASAP, thanks heaps!!

Ben

 

[btproductionsaustralia]

Hey Gswan, you there?

I tried using the voltmeter on the transistors as you suggested and the results are below

Q B C E
2 1.64 2.46 1.73
3 2.47 1.91 1.81
4 1.91 29.2 1.53
5 4.72 27.6 4.25
6 27.6 13.2 28.1
7 28.1 13.2 28.7
8 13.2 29.2 12.6
9 12 0 12.6
12 3.9 13.6 3.3
13 13.6 29.2 13
14 12.7 12 12
15 12 29.2 11.5

As you can see Q 2,3,4, 14 and 15 are all out, but the rest I think are tolerable, would you agree?

I then tested all my resistors and sure enough there are some values that aren;t correct, BUT, they are correct in that the colour coding on the resistors tells me they should be correct, but they are reading different values with the multimeter...is this just faulty resistors, or have I damaged them in the construction somehow? and if it was me, how might I have damaged them...

For example I have a 470k resistor that is marked as such, but the multimeter brings it up at only 325k...is this damage? acceptable?
or would a damaged resistor come up as reading 0?

Also, would the position of the potentiometers, change the readings given by resistors on the meter and attack/release boards?

Thanks for all the help!!!

Ben

 

[gswan]

Ben

Clearly there are some construction errors in your module. You need to check the resistor values with one end disconnected from the circuit, or they won't necessarily read correctly (particularly the high value ones). This is due to other components having an effect on the reading.

You need to check the insertion orientation of the transistors and R17. You probably need to check all of the components in the input amp section since these DC voltage values are not correct for an operational circuit.

The same goes for around the GR amp section.

Geoff

 

[btproductionsaustralia]

Hey Geoff,

I've been going over the resistors and transistors as you suggested...I've checked the data sheets for the transistors and ensured they are all in correctly...as I'm using Mnats board the orientation was drawn on anyway, so couldn't really go wrong there...could I ???

I'm having some trouble removing 1 end of the resistors from the circuit to test them not "in-circuit" as I bent them when soldering to hold them in place, and as I don't have replacements for all of them, am hesitant in case I break one...I have now gone through and visually confirmed that all resistors at least should have the correct resistance( i.e. the colours are correct)...

Before I pull 10 or so resistors of the board, is there anything else I could try? Can I test the capacitors with a multi meter? would they have to be disconnected also?
I have read that there is some kind of clip you can use to disengage the component from the circuit without removing it?

I don't want to come across lazy, just don't want to risk damaging my board if not necessary...

Finall, a dumb Q: I have noticed that the sizing for the capacitors C9, C11 and C34 are different, even though they are meant to be the same component...at the moment I have a 47uf 63V in each of these, but C11 and C34 (particularly C 34) required a squashed fit, and I was wondering if a smaller Cap should be used? perhaps the 47uf 35V?

Thanks AGAIN for all your help

Ben

 

[gswan]

Ben,

Don't rely on the orientation drawn on the overlay, it only applies to certain transistors. The 2n5457 FET is the reverse pinout of the BF245A. It depends on what devices you ended up using.

Check for solder shorts around Q2/Q3. Check the resistors R11-R20 and be absolutely sure you have them correct and in the correct holes. Don't rely on the colour code, I have seen variations of brown, red and orange which all look the same. I assume you measured each resistor before inserting it? Check that your electrolytic caps are inserted correctly (C2, C8) although it's unlikely that your problem is related to these.

You need to get the steady state DC bias conditions correct before proceeding any further.

Geoff

 

[gswan]

Finall, a dumb Q: I have noticed that the sizing for the capacitors C9, C11 and C34 are different, even though they are meant to be the same component...at the moment I have a 47uf 63V in each of these, but C11 and C34 (particularly C 34) required a squashed fit, and I was wondering if a smaller Cap should be used? perhaps the 47uf 35V?

You can use a lower voltage cap (35V) if you want in these locations, it doesn't matter. The lead spacing varies a bit over the PCB due to tracking requirements and keeping it single-sided. I used a 100uF 25V for C34, since it is sitting at 15VDC and is only there to maintain a low impedance half-rail supply to bias the opamp.

 

[btproductionsaustralia]

Geoff, ok thanks,

I used BF245A and BC107, BD139 and BD140 for the Trans, how would I check the orientation is correct then? I assume I would only check the transistors that currently have incorrect voltage?


I'll double check those resistors 11-20...I didn't measure before putting them in, BUT I had labelled every resistor packet with the corresponding Numbers on the PCB and was pretty careful, but will scrutinise further...

Thanks heaps

Ben

 

[gswan]

They should be OK with the overlay. The BC107 has a tab marking the Emitter, which lines up with the overlay.

BTW, did you check the hfe of the transistors Q12-Q15 (GR Amp)? They are supposed to be hand selected so that hfe > 250 for best operation.

I think you will find a couple of resistors out by an order of magnitude.

 

[btproductionsaustralia]

Yeah, the BC107 tab is lined up with overlay,

sorry I don't know what the hfe is, or how to check it?

I've checked resistors 11-20 and they are all as should be...

I'll check the resistors around the q12-15 now...

Ben

 

[Kingston]

gswan,

first of all, I really have enjoyed reading your informative website. Then a question,

with the FET matching chapter we are measuring VDS and VGS (voltages). Yet in the excel sheets you have plotted Id (mA), as in current. How does this relate to the VDS?

 

[gswan]

gswan,

first of all, I really have enjoyed reading your informative website. Then a question,

with the FET matching chapter we are measuring VDS and VGS (voltages). Yet in the excel sheets you have plotted Id (mA), as in current. How does this relate to the VDS?

Sorry, this could be explained a little better on the site.
Assuming you have a supply of Vs volts and a drain series resistor of Rd ohms, the Drain current (Id) will be ((Vs - Vds)/Rd) Amps. That is to say, we measure the Vds value (since it is easy to do) and calculate the current through the resistor, which is the same as the current through the FET.

 

[gswan]

sorry I don't know what the hfe is, or how to check it?

There's usually a simple hfe tester on most multimeters these days. You are looking to use the highest gain devices in the GR amp stage and the lower gain devices in the input amplifier stage. It's probably not particularly important at this stage. You need to get the DC bias conditions correct first.

BTW, I assume your power supply voltages are OK.

 

[Kingston]

Assuming you have a supply of Vs volts and a drain series resistor of Rd ohms, the Drain current (Id) will be ((Vs - Vds)/Rd) Amps. That is to say, we measure the Vds value (since it is easy to do) and calculate the current through the resistor, which is the same as the current through the FET.

Thanks for clearing it up. I suspected something along those lines, and was able to make valid measurements already.

 

[btproductionsaustralia]

sorry I don't know what the hfe is, or how to check it?

There's usually a simple hfe tester on most multimeters these days. You are looking to use the highest gain devices in the GR amp stage and the lower gain devices in the input amplifier stage. It's probably not particularly important at this stage. You need to get the DC bias conditions correct first.

BTW, I assume your power supply voltages are OK.

Hey, yeah my power supply voltages check out, 30+ and -10 as outlined in Mnats instructions...I checked that before stuffing most of the board...

I'm pullin my hair out here!!  ???
I've checked resistors 11-20 and the all measure fine, without having to remove them from board...I assume if they measure correct whilst still connected I don't have to disconnect 1 end?
Is there any other components that would especially through out Q2, 3,4? I need t get them right before moving to Q14 and 15...

yours confusedly

Ben

 

[gswan]

Ben,

What's the voltage on each side of R17 (wrt GND)?
Also, confirm the voltages on Q2, Q3, Q4 terminals.

Geoff

 

[btproductionsaustralia]

Geoff

Using q3 as a reference point the closer side of r17 reads 22.7V  and the farther side reads 29.3V...

        B          C            E
Q2    1.64    2.46      1.51
Q3    2.47    1.91        1.81
Q4    1.91    29.2        1.53

Does this indicate anything specific?

Ben 

 

[gswan]

Why would you use Q3 as a reference point?
You need to put your black meter lead onto a GND point and take all measurements wrt this.

 

[gswan]

Are you sure R18 is the correct value?

 

[btproductionsaustralia]

Sorry, I meant q3 as a visual reference!! the black hand was on the ground point...

Will check r 18 now...

yep, it is 22k...

Ben

 

[gswan]

Check the E of Q4, is it shorted to anything? You've got too much current flowing through R18, which  could be due to Q3 being faulty or one of the other resistors wrong in this area. What's the voltage across R20?