Bell and Howell Schools Model 10D 4540 Oscilloscope Repair (Help!)

[AviatorLj]

I recently received a Bell & Howell Oscilloscope from Ebay for repair. One board has all the wires to it cut. I would like help fixing it before I screw anything up! The cathode glows red when powered on... I am pretty sure that's bad. Though I haven't ever looked at a CRT on an opened device, considering the high voltages and considering that being electrocuted is not fun. The cathode ray is powered by some huge Electrolytics, which seem to be in working order. The board that has the wires cut off is almost identical to the one across from the CRT in the picture. It should have two black wires going to the CRT, like the one that looks similar. I hope the pictures will help.

[AviatorLj]

UPDATE:
The CRT is supposed to glow like that. I am trying to find a manual online but have not found one so far. It would be nice if anyone knows where to find one 

[Andy Watson]

The pair of black wires are clearly the drive to the deflection plates of the CRT. If you can't find a service manual or schematic, try looking for a data sheet for the CRT - it will tell you which pins connect to those wires (there will be both X-plates and Y-plates - one pair is already wired).

Do you know why the wires were cut? I suspect there was a reason

[AviatorLj]

The pair of black wires are clearly the drive to the deflection plates of the CRT. If you can't find a service manual or schematic, try looking for a data sheet for the CRT - it will tell you which pins connect to those wires (there will be both X-plates and Y-plates - one pair is already wired).

Do you know why the wires were cut? I suspect there was a reason

I supposed they were deflection wires. Odd that it uses plates instead of coils like in a TV...
The board might have been replaced or something... Or maybe someone was mad at the circuitboard and desoldered it
The ones cut off the Tube are labeled S and M, and the ones that come from the circuitboard's little brother (likely the Y board) are K and J. I know where the two wires go, but not which one goes to which pin.

[Andy Watson]

I supposed they were deflection wires. Odd that it uses plates instead of coils like in a TV...

Not really. Plates respond to voltage - irrespective of frequency. Whereas coils change their response as the frequency changes. TVs are operated at fixed (predetermined) frequencies, whereas oscilloscopes have to cope with a wide range of frequency.

The board might have been replaced or something... Or maybe someone was mad at the circuitboard and desoldered it

I admire your optimism

Apparently it is potentially a re-badged IO-4540
http://www.vintage-radio.info/heathkit/index.htm

[AviatorLj]

Apparently it is potentially a re-badged IO-4540
http://www.vintage-radio.info/heathkit/index.htm

Hence why there are no manuals online...
This discovery might be helpful, thanks!

[AviatorLj]

OK so I have found out the following:
It is a rebadged Heathkit IO 4540.
The board in question is th Vertical Deflection Board. I will find out as much as I can from the manuals online.

[AviatorLj]

You can find the schematics here: http://elektrotanya.com/heathkit_io-4540_5mhz_triggered_oscilloscope_sm.zip/download.html
Can someone help me decode these? I am a bit overwhelmed. I will post some more detailed pics.

[tyguy2]

I would check to make sure all the components on the possibly failed board are working. If you have any failed components, you could replace those, which could be the first step to repair.

[tautech]

Bit of info in this thread from last year
https://www.eevblog.com/forum/repair/bell-howell-schools-oscilloscope/

[AviatorLj]

Bit of info in this thread from last year
https://www.eevblog.com/forum/repair/bell-howell-schools-oscilloscope/

That' a different model but still helpful, thanks!

[FlyingHacker]

That was my thread from last year. I never did get that thing fully functional, after replacing almost everything. I am guessing design flaw, though I still want to get a HV oscilloscope probe and check it out.

You in good order with the manual, now?

[AviatorLj]

That was my thread from last year. I never did get that thing fully functional, after replacing almost everything. I am guessing design flaw, though I still want to get a HV oscilloscope probe and check it out.

You in good order with the manual, now?

This is a different scope, but I have found a small amount of documentation. This includes a block diagram and a full schematic. It's available here: http://elektrotanya.com/heathkit_io-4540_5mhz_triggered_oscilloscope_sm.zip/download.html
If anyone is able to actually read schematics and pictures and discern where the wires go, I would love their input. I will try to include some more detailed pictures.