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Old 24th May 2017, 10:10 pm   #1
Studio263
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Default MX1500 - B&O bathtime!

I picked up a B&O MX1500 at Mikey's meetup a few weeks ago, this was B&O's only small colour set (15") and styled to match the other models in the MX series. The UK catalogues called it B&O's beautiful baby, you can see why.

The original 20" MX2000 used the Nordmende ICC3000 chassis because the B&O 77XX wouldn't fit into the shapely cabinet, then the Thomson ICC5 was used in the MX3000 (21") and MX4500 / MX5000 (both 28"). The MX1500 was far to small for any of these so the Philips CP90 chassis was chosen. Of the then current designs available on OEM terms that would drive a suitable tube this wasn't a bad choice, it is certainly a compact assembly.

Most Philips CP90 sets seen in the UK were also built here but the complete MX1500 was made in Italy, the only B&O part being the Beolink 1000 remote control unit. For B&O applications, the front mounted AV sockets were removed, along with all the control keys. A re-programmed microprocessor was used which worked with B&O's HF (455KHz) remote control system and the set's control sequences were altered to suit the keys of the Beolink 1000. All had UHF / VHF tuners but surprisingly for an expensive set the teletext decoder remained an option. This was the last B&O TV set with mono sound, a slightly bigger loudspeaker was used, backed with a big block of sponge to damp out cabinet resonances.

This MX1500 was a bit grubby and a bit smelly to the first thing to do was to strip it down to its basic parts and put everything bar the PCBs and the loudspeaker into the bath - see picture! The water turned really dark brown but the set came out looking much better. The white parts of the cabinet are painted and some automotive compound paste got the colour back to its original brilliant white.

Looking at the chassis, there was plenty of the expected poor soldering so I went over all the usual CP90 things - LOPT, frame output transistors, SCART socket, most of the power supply etc. With this done and everything back together off it went, until the aerial was plugged in.

The B&O version of the CP90 has an extra switch behind the mains on/off pushbutton which activates the search tuning. When the set was on, it would search all the time, showing stations briefly as the tuner passed them. CP90s suffered more than their fair share of microcomputer problems due to the proximity of the chip to the bottom of the tube bowl, a stick-on shield was provided later to improve reliability. This seemed to be the obvious cause of this set's troubles, but I also spotted that in the past the memory battery had leaked, turning the corner of the PCB where the switches are an odd colour. A look at the circuit showed that the "search" switch was simply placed between the +5V rail and an input pin of the micro with no pull-down resistor, so any leakage in the board was bound to lead to trouble. Keen to try anything, I added the nearest suitable resistor to hand (82k, but anything between 10k and 100k would do) between the micro side of the switch and the digital ground. Instant sucess, a working set!

The tubes have a hard life in these as the contrast screen on the front is very dark, but this one wasn't too bad. The focus was perhaps a little soft, but it seemed to improve with use. I left the set on for the rest of the evening and it performed perfectly.

The next morning though, just a buzz from the power supply and the 95V rail down at 17V. Disconnect the base of the line output transistor and load the rail with a 60W bulb and its 95V again. Blue disc ceramic capacitor across the line transistor C-E pins OK. You've guessed it, the LOPT had gone. Rats. Hopefully my "wanted" post will turn someting up though, I'd like to get this one going again.

The final picture shows the set with a "real" B&O portable, the Beovision 600. In 1990, B&O fitted their own chassis to the MX series. This was the Unity 1, so called because it fitted into the whole range. The smallest size was 21", they never made small sets again after the MX1500. The Unity 1 and Unity 2 were fine receivers though, and B&O through and through.
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Old 25th May 2017, 1:50 am   #2
Maarten
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Default Re: MX1500 - B&O bathtime!

Nice write-up and good to see this set in a nice condition again.

Just a small off-topic question (maybe worth its own topic if it sparks interest). Are you sure the CP90 was ever made in the UK? If that's the case, it might be the last chassis produced there instead of the 2A.
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Old 25th May 2017, 11:06 am   #3
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Default Re: MX1500 - B&O bathtime!

Interesting write up, shame about the LOPTY! Hopefully one will turn up.

I quite fancied one of these a few years back, but ended up with an MX2000 instead, which still holds the record of the largest TV ever posted to my house! And it survived it too, probably because it's so solidly built. That's got all kind of tuning troubles itself, is it supposed to count from 0-99 when tuning?! I was thinking it'd be more sensible to count 21-69... I might sell on that set soon anyway, as I've got too much stuff! it's a white one, so would go nicely with your MX1500!

Regards,
Lloyd.
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Old 25th May 2017, 11:04 pm   #4
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Default Re: MX1500 - B&O bathtime!

Hi

I repaired quite a few Philips CP90 sets and also came across a 15" version which used a FST tube rather than the normal gold fish bowl. The emission wasn't that great and wondered if the 15" FST tubes didn't last as well as the more conventional 14" types.
Regarding the LOPT, I found a fair number of CP90 sets required a replacement but interestingly, the large screen CP110 LOPT was ultra reliable and I never had to change any. Both the CP90 and CP110 were a good chassis, most problems were due to the 2.4V NiCad memory back up battery and occasional problems with the Toshiba microcontroller IC. The correct suffix to the part was important regarding whether the set had basic Teletext or full level one Teletext (Fastext).
I also vaguely remember there was a modification to the 6MHz intercarrier circuit involving a small modification board and replacement ceramic filter.
I still regularly use my 24" CP110 set that's given stirling service from new in 1989, and the CRT is very good.

Regards
Symon.

Last edited by Philips210; 25th May 2017 at 11:25 pm. Reason: typo
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Old 26th May 2017, 1:14 am   #5
Maarten
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Default Re: MX1500 - B&O bathtime!

I forgot to mention in my previous message; the LOPT is one of the more common types so one will turn up without a doubt.
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Old 26th May 2017, 8:04 am   #6
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Default Re: MX1500 - B&O bathtime!

Hello Maarten,

Here are some pictures of a UK-built CP90, taken from the cover of the March 1993 issue of 'Television' magazine. I've included a close-up of the label, I think this one was a 21" model.
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Old 26th May 2017, 2:25 pm   #7
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Default Re: MX1500 - B&O bathtime!

There was a 17" version as well in FST guise - that's Philips, not B&O. They didn't sell all that well as the price was the same as the 21" version. More inches for your money!
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Old 26th May 2017, 3:31 pm   #8
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Default Re: MX1500 - B&O bathtime!

Quote:
Originally Posted by Philips210 View Post
I still regularly use my 24" CP110 set that's given stirling service from new in 1989, and the CRT is very good.
So you got the good CP110 then Symon.
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Old 26th May 2017, 8:59 pm   #9
Maarten
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Default Re: MX1500 - B&O bathtime!

Quote:
Originally Posted by Studio263 View Post
Hello Maarten,

Here are some pictures of a UK-built CP90, taken from the cover of the March 1993 issue of 'Television' magazine. I've included a close-up of the label, I think this one was a 21" model.
Thank you! That's quite clear. The 2A may still be the last UK design (full or partial) but this CP90 was produced in late 1987, so there was still at least some production of TV sets after the 2A.
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Old 26th May 2017, 9:04 pm   #10
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Default Re: MX1500 - B&O bathtime!

Hi Neil.

The CP110 is by far the best set I've owned. It's now 28 years old and in all that time the only work required has been 3 memory back up batteries, a microcontroller IC, the main smoothing capacitor after the bridge rectifier and a few dry joints including the SMD Fastext board. It still has it's original CRT and LOPT. The emission of the CRT is pretty respectable. Oh, I did actually blow up the power supply due to a careless moment with the oscilloscope but it was a simple rebuild. The auto grey scale works well probably due to the three guns having a fairly balanced emission.
I repaired a few CP110s and always found them to be reliable, actually more reliable than the CP90 I think. Some have said the 45AX CRT in the CP110 doesn't properly display reds very well, bordering on the orange side but I can't say I've noticed this. Perhaps it was a problem with the early production run sets.
There's a lot to like about the CP90/CP110 chassis as parts were reasonably priced and the excellent service information from Philips was second to none. I wish today's TVs could be built like this.

Regards
Symon.
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Old 27th May 2017, 1:39 am   #11
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Default Re: MX1500 - B&O bathtime!

Being American it took a while to figure out "LOPT" ,
but "LOPTY" has me stumped!

What?
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Old 27th May 2017, 12:25 pm   #12
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Default Re: MX1500 - B&O bathtime!

Same thing, we also occasionally see LOPTX used too!
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Old 27th May 2017, 8:11 pm   #13
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Default Re: MX1500 - B&O bathtime!

It's especially confusing with more modern sets, wheren"LOPT" could be short for "line output transformer" or "line output transistor" !

I'm almost a little surprised that the abbreviation "LOPV" (for "line output valve") was not retained even when the "valve" was actually a transistor (a transistor is still technically a type of valve, after all) for the avoidance of ambiguity; but perhaps this might have ended up been more confusing to anyone (perhaps not unreasonably) expecting a traditional, thermionic valve in this position.
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Old 28th May 2017, 1:07 am   #14
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Default Re: MX1500 - B&O bathtime!

As far as I'm aware the most common short form for the line output transistor is HOT.
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Old 28th May 2017, 7:33 am   #15
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Default Re: MX1500 - B&O bathtime!

In case you have not twigged (post 11)
LOPTY was the way we used to pronounce the word when describing a line output transformer although still normally spelling as LOPT. American way Hor sweep or flyback?
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Old 28th May 2017, 5:20 pm   #16
dtvmcdonald
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Default Re: MX1500 - B&O bathtime!

In the US its an HOT. But unfortunately in fact the T really can be Transformer,
Tube, or Transistor. There's no way to know unless explained! Yes we usually say flyback
but HOT is common too.

But here we don't have VOT's and I believe you don't have FOT's.
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Old 28th May 2017, 5:55 pm   #17
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Default Re: MX1500 - B&O bathtime!

If I had to use abbreviations in a conversation, the LOPT (pronounced loptee) was always the transformer. The transistor could've been described as anything, line transistor, output transistor, line output transistor, all clear in the context of the discussion.

There's a forum member on here who had one of those B&O sets in the kitchen. I think he was fitting new units or something similar and the tube ended up attracting all the dust which found its way to the wrong side of the glass! Not so easily wiped clean..
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Old 28th May 2017, 7:11 pm   #18
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Default Re: MX1500 - B&O bathtime!

Quote:
Originally Posted by Studio263 View Post
Here are some pictures of a UK-built CP90, taken from the cover of the March 1993 issue of 'Television' magazine.
Good heavens......I wrote that article.....was it really all those years ago?? I wonder how many more of these and the CP110 (which I covered a few months later) are still about 24 years later?
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