Monitor Scope accessories for the FT-101 Station
The YO-100 Monitor- scope consists of a monitor of "On the air" signal and an oscilloscope. A two tone signal generator is built-in for SSB adjustment, and the cabinet design of the YO-100 and YO-101 matches that of the entire family of equipment in the Yaesu FT-101 series, FT-277/FT-201 transceivers, FR-101, FL-101 Twins.
The rear panel of the scope has two 50-75 ohm coaxial connectors (SO-239) for signal in and out to monitor the transmit signal path.
Working the bugs out of a YO-100
This was the best of two YO-100 scopes to come by my path in the last few months. So I thought I'd step you through a couple of the more commonly seen problems you are likely to encounter if you own one of the gems.
More often then not one of two problems will occur in these scopes as they age. Shortened sweep, no sweep, or user unable to focus the trace. A monitor scope is nothing more then an oscilloscope that's a whole lot less complicated! All oscilloscopes and television sets need a sweep oscillator for a horizontal trace to be presented on the screen to display the trace from left to right. This particular unit had a severely shortened sweep. The sweep Generator PB-1276 was working but the voltage gong into this unit was too low being pulled down by a shorted zener diode and a smoking 100 Ohm resistor. A little common sense and use of a highly calibrated eyeball revealed a black spot on the tone generator board PB-1275 and what looked like a capacitor that became just a tad bit warm.
In the small schematic to the left you are looking at the zener diode regulator D101 a 25v zener diode
The zener D101 in this case was shorted, R126 our 100 Ohm resistor was burning up and the capacitors you see on the right ( C111) show signs of extreme heat. Since I was working on two of these units at the same time, I decided to pull the caps out of both scopes. Both revealed heat stress and as you can see one was ready to blow it's top off! If you own a YO-101 scope I highly suggest you inspect this area of your scope. This two tone oscillator board can be found on the top side of the chassis directly next to V2 a 12BY7A valve.
Just like the schematic shows D-101 resides right next to C111
This small circuit resides on the Tone generator board PB-1275
(Provides 1900 Hz and 1500 Hz for two tone generator)
In this photo you can see where PB-1275 sits directly next to V2
Replacing D-101, R126 and C111 restored our sweep.
The Zener is suppose to regulate 25 at volts, but 26 is close enough using an NTE5028A Zener Diode.
The second problem you're most likely to encounter if you own a YO-100
is the inability to focus the horizontal trace
If this happens to you check R22 a 330K Ohm resistor for an open circuit. This resistor can be found between VR5 intensity control and VR6 the focus control due to the high voltages on the circuit, this is also a common failure item in these scopes
Be very careful working in this unit with the power on, there is roughly 1,200 volts floating on R22
While this problem is not bad enough to warrant replacement of the CRT tube, on the left photo you can see CRT Trace burn in. This is what happens when you leave the intensity turned up too long in one place. I recommend if you're not using the scope to turn down the intensity control. On the right you can the same CRT in another unit that is still in good condition. If this were a television set and you saw a single white line, this problem, it would be indication that your vertical deflection circuit took a powder! Any time you have an Oscilloscope or monitor scope, it's always important to turn down you intensity to ensure long life of you CRT in order to avoid the burn in problem as noted in the left photo.
A look into the bottom of the YO-100
Rectifier Unit A PB-1271 Provides 600vdc & 300 vdc
At the Top of this photo you see rectifier
Unit B PB-1272 -1200 volt DC supply & 30 Vdc supply for transistor circuits
Sweep Generator board PB-1276
generates a saw tooth signal for the CRT deflection plate
The sweep freq is varied from 10 Hz to 10 KHz by a front panel control
While you're at it and you have your scope apart, you might as well do a little house cleaning under the bonnet!
Now you can see all my cleaning secrets !!
When all is said and done, repairs are made and the scope is
as clean on the inside as it is on the outside
you will have something you can be proud of in your shack !
From the Fox Tango Forum.
You can use a 3RP1 CRT in place of the NEC CRT.
There are two (2) types of 3RP1 CRTs...One has a relatively flat face while
the other may be slightly convex. Both will work, but the flat face unit
is preferable. You will also need to change the socket to accommodate larger based
3RP1. Both CRTs are electrically alike. I had to make the mod to my
YO-1Ø1 and it works just as well as the original NEC CRT. Jay/AF2C
PDF Data sheet for RCA 3RP1 CRT
YO-101 Instruction Manual and schematics
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