Bell and Howell Schools Model 10D 4540 Oscilloscope Repair (Help!) - Page 1
Forum section: electronics / repair

author: AviatorLj
author_rank: Contributor
timestamp: February 19, 2016, 12:01:48 am
content: 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.

author: AviatorLj
author_rank: Contributor
timestamp: February 19, 2016, 12:37:55 am
content: UPDATE:The CRTissupposed 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

author: Andy Watson
author_rank: Super Contributor
timestamp: February 19, 2016, 12:50:42 am
content: 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

author: AviatorLj
author_rank: Contributor
timestamp: February 19, 2016, 12:55:24 am
content: Quote from: Andy Watson on February 19, 2016, 12:50:42 amI 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 itThe 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.

author: Andy Watson
author_rank: Super Contributor
timestamp: February 19, 2016, 01:03:23 am
content: Quote from: AviatorLj on February 19, 2016, 12:55:24 amNot 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.QuoteI admire your optimismApparently it is potentially a re-badged IO-4540http://www.vintage-radio.info/heathkit/index.htm

author: AviatorLj
author_rank: Contributor
timestamp: February 19, 2016, 01:08:16 am
content: Quote from: Andy Watson on February 19, 2016, 01:03:23 amHence why there are no manuals online...This discovery might be helpful, thanks!

author: AviatorLj
author_rank: Contributor
timestamp: February 19, 2016, 01:11:49 am
content: 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.

author: AviatorLj
author_rank: Contributor
timestamp: February 19, 2016, 01:57:36 am
content: You can find the schematics here:http://elektrotanya.com/heathkit_io-4540_5mhz_triggered_oscilloscope_sm.zip/download.htmlCan someone help me decode these? I am a bit overwhelmed. I will post some more detailed pics.

author: tyguy2
author_rank: Unknown
timestamp: February 19, 2016, 03:41:24 am
content: 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.

author: tautech
author_rank: Super Contributor
timestamp: February 19, 2016, 05:10:38 am
content: Bit of info in this thread from last yearhttps://www.eevblog.com/forum/repair/bell-howell-schools-oscilloscope/

author: AviatorLj
author_rank: Contributor
timestamp: February 19, 2016, 09:34:58 pm
content: Quote from: tautech on February 19, 2016, 05:10:38 amThat' a different model but still helpful, thanks!

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: February 23, 2016, 06:51:58 am
content: 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?

author: AviatorLj
author_rank: Contributor
timestamp: February 27, 2016, 01:41:42 am
content: Quote from: FlyingHacker on February 23, 2016, 06:51:58 amThis 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.htmlIf 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.