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#91
08-21-2024, 03:56 PM
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Nope...not entirely. Have a very low power clean 12.5MHz sine wave. The frequency doesn't change whatever I do to the wheel and the output level has no effect on the amplitude. The meter still doesn't move into the readable zone. Going to clean some controls and see what that does.
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#92
08-21-2024, 04:48 PM
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No change with cleaning. When I found the blown fuse, I almost raced to the laptop to cancel my order for the $400+ sweep generator but I didn't and thank goodness. I'll see if the seller wants to buy this one to refurbish. We'll see. I guess we're back on hold again.
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#93
08-21-2024, 06:42 PM
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As I say it is the luck of the draw. As I said mine was something like $35 and I plugged it in and it worked. Even the one you bought I suspect there is not much wrong with it. Could go through it with you on another thread 😉.
Fortunately the 8601a is pretty common.
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#94
08-21-2024, 07:02 PM
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Before you give up on this 8601a, could you run through a few checks? A blown fuse suggests perhaps a power supply failure.
The 1/8A fuse looks like it was for theb-75 volt supply. You should check to ensure it is -75v and while you are at it the +20v supply. The good thing is that after you changed the fuse, you got a 12.5Mhz sine wave. The suggests the hybrid output amplifier is good and the internal fault may be minor. Here is the link to the BAMA stiched schematics. The Power Supply is fig_8_26 https://bama.edebris.com/manuals/hp/8601a/
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#96
08-21-2024, 07:47 PM
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Quote:
The -70 and +20 volt voltages are fine. It's the -6.3 volt line that's suspect. Reading only -3.7V
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#99
08-21-2024, 08:52 PM
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With it powered on, are you able to find the correct voltages?
From your picture below and from the board layout in the manual, the edge connections at the bottom of your photograph run from 1 on the left to 15 on the right. measuer with respect to ground (chassis): 7-9 is +20v 10-12 is -6.3v The the line pointing to the aluminum can of C12 is -75v
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#103
08-22-2024, 02:38 PM
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Here is a bigger view of the removed board. You can't see it too well but the resistor between the heat sinks has a chip on the outside coating that is more than just a surface mar. It reads 136 ohms. All of the electrolytic caps I can measure are about 20% high.
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#104
08-22-2024, 04:32 PM
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Looks like it's a 130 ohm (R4?) resistor so that's fine and 20% high is fine too.
Odd half wave power supply design with the center tap being the -6.3 volt rail. Could be as simple as CR2 being bad. Looks like it's there for protection. Perhaps it is same to disconnect the load form this board and measure the voltages? That way you could isolate the problem to this board or what it is powering. Last edited by bandersen; 08-22-2024 at 04:41 PM.
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#105
08-22-2024, 10:37 PM
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So if the Power Supply components are good (as I suspect they are) then one of the circuits is loading the -6.3v down.
I researched where the -6.3v and it goes to the boards listed below. The first thing I would do is to lift the -6.3v one at a time to each board until the until the voltage pops back to -6.3v: A6 Video Amplifier Assy A5 VTO A4 Crystal Oscillator/Mixer A3 Loop Amplifier/Crysatl Calibrator A2 Divider/Divider Bypass When you identify the board, I believe there is a good chance that is where the overall problem is.
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Linear Mode
