interleaved:
On 3/2/2022 7:06 AM, James55 wrote:
Morning all and thank you for the help.
I was a bit tired last night and didn't provide the correct nor complete information, as in amongst all the 'de-' and 're-' soldering,
the minus 8v AC wires had become shorted. The correct DC readings at the test points are;
140v - 25v
65v - 21.54v
15v - 3.705
5v - 0.000
-8v - 0.625
-15v - 0.615
Disconnecting the Bridge rectifiers gives the following AC readings;
CR1721 (65v rail) - 47.53v
CR1751 (15v) - 12.96v
CR1761 (5v) - 6.58v
CR1771 (-8v) - 7.34v
CR1781 (-15v) - 12.34v
If you disconnect the bridge rectifiers (and I assume from the + end, so that they are still connected to the transformer), then what you measure at the + rectifier terminals will be pulsating DC.? What this does test is that the rectifiers themselves are not shorted, one still may be open, though.
The transformer still draws some current due to the core losses, and whatever is directly connected AC wise to the transformer.
The reference voltage tests at around 108v.. In the manual it says either 160 or 140 volts depending on where you read it.
One thing which may be worth noting, is that with all five bridge rectifiers disconnected, the dimbulb still glows.
@ Harvey...
It is a linear power supply.
I shall disassemble the unit more when I have time later today.
Shall be looking further into the reference voltage as right now all the LV rails are disconnected before the bridge rectifiers. Not quite sure I understand the manual though. On the power supply diagram page the reference voltage rail terminates with an arrow... It says, 'S1403B' (a switch) and also has a hexagon with the number '10' inside of it. I assume that the '10' links to a corresponding '10' on a different board?
Which -50v supply are you referring to?
Look at the power supply regulators, one will have extra circuitry taking a DC voltage and running it through a zener diode.? This is the only supply that is standalone.? The manual will tell you so.? The S1403b is a destination, the "10" is schematic sheet on which to find it.? In this supply, you'd want the on-board connections to the DC reference voltage.? Reading the theory of operation is important for these scopes because tektronix is very thorough about such things.? If there's a troubleshooting procedure, follow it.
If you wish more information of a general nature about linear power supply regulators (and tektronix is highly specific per scope), then there are a number of posts concerning 400 series scopes and power supplies.? 7000 series scopes use different supplies.? I'd also recommend searching out the theory of linear regulators.
Harvey
@Dave..
That is what I would have expected and to be honest there have been some shorted tantalums, but I have lost count of how many caps have now been tested. It is time to disconnect more boards until at least the 'area' is identified.
I'll report back either late tonight of tomorrow morning.
James
