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Source of TR7 Audio Hash Found

Craig W8CS All Messages By This Member #83104 Last week I had a nasty 1000Hz tone start coming up in my RX audio on the TR7. I tried the usual hacks, replaced C2108 in the power supply board. No Bueno.? ? The noise varied with the digital readout numbers, so I then noticed that the DR7 board has its own 5V supply. I put a scope on the big filter cap there and saw 2V p-p of 1000Hz tone!? ? Here is a showing this.? ? Next problem to resolve is that the passband control is all screwed up again. Neither the PBT control nor the PS pots vary the 5.645 MHz signal. I'm inclined to think that it should follow the path of the most recent soldering excursion...(i.e. what did you $%^&* with most recently?) -- Craig/W8CS Greenville, SC
Jim Shorney All Messages By This Member #83123 On Sun, 23 Feb 2025 11:29:46 -0800 "Craig W8CS via groups.io" <craig_severson@...> wrote: The noise varied with the digital readout numbers You could have lead with that. :) That was the next cap I would have pointed you to. It does not fail often but they are getting old. Nice catch. Here is a quick video ( ) showing this. Next problem to resolve is that the passband control is all screwed up again. Neither the PBT control nor the PS pots vary the 5.645 MHz signal. I'm inclined to think that it should follow the path of the most recent soldering excursion...(i.e. what did you $%^&* with most recently?) Follow the control voltages from the fixed passband pots to the PBT/Ref board. All of the switching magic happens in U1001. -- 73 -Jim NU0C
Craig W8CS All Messages By This Member #83126 Thanks as always, Jim.? ? I should be able to bypass all of the fixed passband values from the PS board (at least on RX) by using the PBT control.? ? Same problem; the PBT control does not alter the 5.645MHz signal. I've tried shotgunning in a spare PBT board with no change. The unit "receives" but it's what you'd expect with the passband being off-center.? ? This is a strange one; it's almost like the +10V has lost ground reference to the PBT board. The PBT control is just a voltage divider between +10V and gnd and the signal into the PBT board never goes below about +7.5V.? -- Craig/W8CS Greenville, SC
Jim Shorney All Messages By This Member #83127 If you lost ground on the PBT/REF board is seems likely that you would have many more problems. More likely perhaps that you have lost something on the PS board. There are two independent grounds on the PS. What do you see if you measure directly on the pots? The passband control voltages are switched by U1001 on the PBT/REF board. Switch control voltages to U1001 are selected by the PBT and filter switches, Mode switch, and T/R switching. Follow the DC. On Tue, 25 Feb 2025 03:12:50 -0800 "Craig W8CS via groups.io" <craig_severson@...> wrote: Thanks as always, Jim. I should be able to bypass all of the fixed passband values from the PS board (at least on RX) by using the PBT control. Same problem; the PBT control does not alter the 5.645MHz signal. I've tried shotgunning in a spare PBT board with no change. The unit "receives" but it's what you'd expect with the passband being off-center. This is a strange one; it's almost like the +10V has lost ground reference to the PBT board. The PBT control is just a voltage divider between +10V and gnd and the signal into the PBT board never goes below about +7.5V. -- Craig/W8CS Greenville, SC -- 73 -Jim NU0C
Dieter Horst All Messages By This Member #83128 I had similar symptoms on my TR7 and the culprit turned out to be U1001. Before that, I had plugged in the PS board with one pin offset. That obviously killed the switch U1001. I bet something like that happened here. 73, Dieter DL5RDO Von meinem iPhone gesendet toggle quoted message Show quoted text Am 25.02.2025 um 13:59 schrieb Jim Shorney via groups.io <jimNU0C@...>: ? If you lost ground on the PBT/REF board is seems likely that you would have many more problems. More likely perhaps that you have lost something on the PS board. There are two independent grounds on the PS. What do you see if you measure directly on the pots? The passband control voltages are switched by U1001 on the PBT/REF board. Switch control voltages to U1001 are selected by the PBT and filter switches, Mode switch, and T/R switching. Follow the DC. On Tue, 25 Feb 2025 03:12:50 -0800 "Craig W8CS via groups.io" <craig_severson@...> wrote: Thanks as always, Jim. I should be able to bypass all of the fixed passband values from the PS board (at least on RX) by using the PBT control. Same problem; the PBT control does not alter the 5.645MHz signal. I've tried shotgunning in a spare PBT board with no change. The unit "receives" but it's what you'd expect with the passband being off-center. This is a strange one; it's almost like the +10V has lost ground reference to the PBT board. The PBT control is just a voltage divider between +10V and gnd and the signal into the PBT board never goes below about +7.5V. -- Craig/W8CS Greenville, SC -- 73 -Jim NU0C
Craig W8CS All Messages By This Member #83142 Thanks Dieter and Jim. Swapping to my spare PBT board resolved the issue and the passband works again. (not sure why that step did not work before) Very likely I did the same as Dieter and plugged in PS board wonky and took out that U1001.? ? More stuff from Mouser to order. Cheers gents.? -- Craig/W8CS Greenville, SC

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