Date
1 - 20 of 47
QDX IC7 Voltages
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Philip <philip.g7jur@...>
I am having a problem with my QDX, the voltages on pins 3 and 5 on IC7 are measuring 905 mV.
When using IQ mode I get a mirror signal when using a SDR program. Philip G7JUR |
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Alan G4ZFQ
On 14/09/2022 21:36, Philip wrote:
I am having a problem with my QDX, the voltages on pins 3 and 5 on IC7 are measuring 905 mV.Philip, If this is a rev3a board have you cut the track as described in the latest manual? Section 2.3a. 73 Alan G4ZFQ |
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Philip <philip.g7jur@...>
Yes I did cut the track
Philip g7jur |
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Alan G4ZFQ
On 15/09/2022 07:42, Philip wrote:
Yes I did cut the trackPhilip, Similar fault. What voltages each side of R39? (100K) 73 Alan G4ZFQ |
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Philip <philip.g7jur@...>
Do you mean R36 LCOM side is 2.544 Volts other side is 2.044 Volts, should be 2.949 Volts. I have ordered a new LM4562 to replace IC7, but not 100% convinced that is causing the fault. Every thing on the side of IC9 looks good.
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Philip <philip.g7jur@...>
Not 2.949, I ment 2.544 Volts
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tim born
Tangent - Is the Rev3a board labeled differently from the Rev3 board on the silk screen?
Also, what's this reference to cutting a trace? I went looking for latest QDX docs , which is labeled "Assembly manual for PCB Rev 3a (document version 1.13 published 15-Sep-2022)" on the link, but labeled "PCB Rev 4" on the first page of the docs. > If this is a rev3a board have you cut the track as described in the latest manual? Section 2.3a. Section 2.3 of this latest QDX docs appears to be a single page photo "Inventory Parts". Would like to understand this "cut the trace" idea. I built a Rev3 and missed that memo. 73 -tim N7TDB |
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Jim Strohm
Tim, this was a problem with the 33A board only, which is prominently
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labeled "3A". 73 Jim N6OTQ On Thu, Sep 15, 2022 at 9:07 AM tim born <timothy.d.born@...> wrote:
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Alan G4ZFQ
On 15/09/2022 14:07, tim born wrote:
I went looking for latest QDX docs <http://qrp-labs.com/images/qdx/manual_1_13.pdf>, which is labeled "Assembly manual for PCB Rev 3a <http://qrp-labs.com/images/qdx/manual_1_13.pdf> (document version 1.13 published 15-Sep-2022)" on the link, but labeled "PCB Rev 4" on the first page of the docs.Tim, Hans must answer this! It has just taken the place of manual_1_12 which is where the mod is (was!). "2.3a Fix PCB Rev 3a board fault! Regrettably, somehow a copper fault crept into the Rev 3a PCB layout, causing a short circuit from a via to the ground pad of capacitor C41. This is ONLY a problem on the Rev 3a board, which is clearly indicated on the silkscreen as shown below." At the moment this manual exists on some computers but not the web site.. 73 Alan G4ZFQ |
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Tim, it looks like Hans updated the instructions for the Rev 3a board to the Rev 4 board and removed the part about eliminating the short. It was step number 2.3a, right after step 2.3 ... Inventory Parts in the Rev 3a manual. The reference to step 2.3a is still in the table of contents but it doesn't go anywhere. I'm sure he will correct that ... Ron On Thu, Sep 15, 2022 at 7:15 AM Jim Strohm <jim.strohm@...> wrote: Tim, this was a problem with the 33A board only, which is prominently |
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Alan G4ZFQ
On 15/09/2022 14:27, Alan G4ZFQ via groups.io wrote:
At the moment this manual exists on some computers but not the web site..http://qrp-labs.com/images/qdx/manual_1_12.pdf But not indexed. |
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Hans Summers
My apologies for the confusion I have put back the Rev 3a manual 1.12. Which is the correct current version. I had not finished editing the 1.13 manual and I have deleted it until it is ready. Please ignore 1.13. 73 Hans G0UPL http://qrp-labs.com 73 Hans G0UPL http://qrp-labs.com https://www.buymeacoffee.com/g0upl -------- Original message -------- From: Alan G4ZFQ <alan4alan@...> Date: Thu, Sep 15, 2022, 5:41 PM To: QRPLabs@groups.io Subject: Re: [QRPLabs] QDX IC7 Voltages On 15/09/2022 14:27, Alan G4ZFQ via groups.io wrote: |
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tim born
Alan et al -
Thanks for that clarification (and a copy of "the missing manual"). I now know the secret handshake. Hoping not to need it, but I have another QDX on order, so not clear which version will arrive. Be Prepared -tim N7TDB |
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phil - wb4som
I have been looking at this problem on and off since I got my QDX - there was also a 2 week trip to Scotland in there so it's really only been a couple of days. What I've found is that (some) LM4562s have an input bias 'latch-up' issue when powered up with a large common-mode input voltage. On the QDX this is the case. Unfortunately I've done a small butchery on my QDX - hopefully repairable with a flywire. I have confirmed this latch-up on a proto-board with an LM4562 which I had replaced on my QDX only to see the same issue. I'm about to change the 470K input bias resistors to 100K to test it in the application - more to follow.
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phil - wb4som
I should add that the issue seems appears with a hi-z input impedance - hence the lower values.
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Philip <philip.g7jur@...>
Hi Phil.
Let me know how you get on, as this fault is driving me mad. Philip G7JUR |
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phil - wb4som
The 100K resistors did not fix the lockup on my board. After reviewing the PCM1804 datasheet I realized that the DC blocking caps between the Tayloe mixer and the instrumentation amp were not needed due to the ADCs HP filter. I removed the 4 caps and soldered down some jumpers. All is fine now and the amps have some dynamic range on the low side. Last night I thought about whether removing the 10uf caps (C64 and C68) might also solve the issue - the inputs would not be held at the lower rail during power up. If someone else runs into this issue it might be worth a try. |
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Philip <philip.g7jur@...>
Done the mod to my QDX, now working correctly
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Denis - EI6IF
Seeing the same problem here. 2.460 volts on the mixer side of the dc block caps. On the op-amp side C71 and C72 have 0.912 volts. C73 and C74 have 2.388 volts.
Too late in the night to start anything now but shorting out each of C71 - C74 is likely to solve the image rejection problem I am seeing? 73 Denis |
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phil - wb4som
There may be a couple of other ways of getting around this while maintaining the ac coupling of the original topology. I'll take a look at what I can on the protoboard - AFTER COFFEE - this morning. The would involve removing the 10uF cap, and/or changing the resistor values. I've packaged my QDX now and really don't want to be moving parts around on it, it's been trough a lot of hot air, so one of you might need to verify on a real QDX. BTW, I looked at the TI analog forum this morning and there are other instances of this happening with single rail supplies. Going to drink coffee now and play on 40M JS8 running my QDX.
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