Yep. Already in my plans to do so. Given the heat that resistor should have been producing, I'm a bit surprised the board isn't discolored but it isn't. Someone had adjusted the DC LEVEL pot completely to one (CW) stop and that might have accounted for why it wasn't getting hotter than it was. I had tried to adjust that but could not change the voltage at the test point and I surmised that Q714 was slammed fully on and that was due to R710.
I didn't have anything close to 5.62k so settled for a 2.2k a 3.3k in series (1W each) and that at least has me going for now. With things working, though, those two resistors get very warm!
Thanks,
Barry - N4BUQ
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----- Original Message -----
From: "Dave Wise" <david_wise@...>
To: "tekscopes" <[email protected]>
Sent: Sunday, June 5, 2022 9:46:11 AM
Subject: Re: [TekScopes] Another Bad Resistor
Install the new resistors spaced away from the board to dissipate heat better.
Dave Wise
From: [email protected] <[email protected]> On Behalf Of n4buq via groups.io
Sent: Sunday, June 05, 2022 5:56 AM
To: tekscopes <[email protected]>
Subject: Re: [TekScopes] Another Bad Resistor
Hi Mark,
I hadn't done the math but, yes, R710 is run too close to its rating and will go
with something more that 1/2w for it.
I haven't done anything to the power supply yet. Voltages check very close but I
think I'm getting more ripple on at least one rail than should be there and
will need to replace some of those caps. Will try to remember to check that
zener while I'm in there.
Thanks,
Barry - N4BUQ
----- Original Message -----
From: "Mark Vincent"
<orangeglowaudio@...<mailto:orangeglowaudio@...>>
To: "tekscopes" <[email protected]<mailto:[email protected]>>
Sent: Saturday, June 4, 2022 10:17:43 PM
Subject: Re: [TekScopes] Another Bad Resistor
Barry,
This resistor was underrated in wattage from the factory. A 5600 ohm 2W will
work. The wattage should be 2W. R714 should be 2W. R717 should be 1W and so on
throughout the scope. I wonder if VR982, 9V zener in the power supply, is open?
If so, use BZX85B9V1.
Mark
