Vintage Products

Re: Beomaster 2000 recap - What do I need?

Dillen — Sun, 14 Mar 2010 09:36:17 GMT

I have some new TCA4500's in the drawer if you cannot find one locally.
They are not SMD's though but standard DIL which I seem to remember is correct for the BM2000,
I'm sure you can confirm this.

Martin

Re: Beomaster 2000 recap - What do I need?

Trigi — Sun, 14 Mar 2010 06:37:57 GMT

Got a lot of old 1900 and 1900-2´s

Maybe the chips are the same, ill try to open one of them.

Best R.

Trigi, Denmark

Re: Beomaster 2000 recap - What do I need?

Stoney3K — Sun, 14 Mar 2010 05:07:08 GMT

Dillen:

I always considered them fairly reliable but I've seen a couple
of dead TCA4500's recently.
Why not just replace the chip and see if that cures the poor thing ?

Well, the internal oscillator (pin 15) doesn't show up on my scope display. It only seems to get DC voltage, no oscillation.

IIRC the 19KHz should always be present, even if there's nothing connected to the signal input, since it's part of the VCO free running frequency. The PLL locks on the 19KHz pilot tone and this brings the 38KHz oscillator (taken from the same frequency divider) in phase with the subcarrier. Since I can't do any measurements on the inner workings of the chip, I'm pronouncing it dead.

The next challenge is to find a replacement for this old chip! I've come across some part numbers of compatibles (CA758/UA758/LM1800), but none seem to be in active production anymore. Seems these days, manufacturers go for single-chip FM stereo tuners. Time to hunt up some NOS, or someone might have a dead Beomaster lying around with a working chip...

Re: Beomaster 2000 recap - What do I need?

Dillen — Sun, 14 Mar 2010 03:31:12 GMT

I always considered them fairly reliable but I've seen a couple
of dead TCA4500's recently.
Why not just replace the chip and see if that cures the poor thing ?

I never had an AM version of the Beomaster 2000 on the bench, so I'm afraid
I cannot give much advice regarding the AM issue.

Martin

Re: Beomaster 2000 recap - What do I need?

Stoney3K — Sat, 13 Mar 2010 20:43:49 GMT

OK, little update on the tuner fix-attempt:

I took the whole unit apart today and decided to start some trouble-hunting. More to the point, I needed to get the stand-by button fixed anyway, so I figured it would be a good opportunity to do some testing on the tuner section.

So I connected the whole tuner bit up again, did some fiddling about, and discovered that the AM receiver, although working, was refusing to mute itself and was the source of all the AF noise crudding up my inputs. A quick disconnect of the receiver's AF output, and the PH and TP inputs were once again quiet -- and amazingly, I could suddenly receive FM stations even though there was nothing connected to the aerial socket.

2 feet of wire later, and the FM receiver was crystal clear. I believe the AF output of the AM section was contaminating the FM receiver logic, seriously messing up the AGC and AFC, leaving me unable to pick up any stations. Having the AM off the bus, the AFC could kick in like it should, and gave me two nice green lights above the STAND BY button indicating there's a working radio inside

On the downside, I couldn't get the stereo decoder to show any signs of life. The FM output is near perfect, in mono, but the stereo decoder would not lock on any stereo stations. Plugging in the scope, it seems that the local 19kHz oscillator wasn't doing much of anything, at all. I checked all the discretes which make up the oscillator and loop filter sections (they were fine), but as the stereo decoder is right in the tuner's signal path, I might need to write a nice eulogy for this trusty old Motorola TCA4500 that's been splitting up channels for so many years.

Right now I'm stuck with mono, but with a working StandBy button (which wasn't working, I was sloppy at putting the panels together last time, and the front panel didn't contact at the StandBy button) and at least I can tune up some stations without having to zap through my DVR box every time. As for the AM goes -- I might fix that one day, in the future, if there's a threat of a nuclear holocaust!

Re: Beomaster 2000 recap - What do I need?

Dillen — Tue, 23 Feb 2010 16:45:52 GMT

Sounds a lot better now.

The 4066 is a CMOS circuit, so would be prone to damage from static electricity
and wrong voltage in general so here I agree on replacing.
If the tuner seems to be working fine, I wouldn't worry too much about it.
If something goes wrong in the tuner, being a fairly low current part
of the Beomaster, it won't kill the whole thing so you can deal with it
if something shows up.
The power supply, eventual decoupling and signal paths would be the places
to focus on when replacing capacitors and you shouldn't need a lot
of instruments (if any at all) to do so.
The adjustments I wouldn't touch unless proven off in which case they would probably
need replacing before readjusting. Trimmers normally don't go out of adjustment
by themselves so any wrong settings would indicate that something else has gone wrong
or the trimmer itself has gone bad.

Not a lot is going on below 2MHz in an FM tuner but if you absolutely need to realign
the tuner, and that would only be needed if some major damage has occured, you
would need a good injection probe and an FM signal generator, preferably capable of
MPX stereo, covering the tuners frequency range.
I use a big Hewlett Packard thingy for the rare occasions but, honestly, I would recommend you bring the
Beomaster in for service if you end up in need of tuner alignment.
The cost of the instruments needed can't be justified if you are only doing one or two repairs of this type per year.
For the AF sections, - again - if you absolutely need to do it, you would need a signal
generator rather than a tape recorder or a CD.
I have a B&O TG7 for this purpose. It's good, it's easy to use, fairly cheap
and, being part of the original B&O instrument series (what most
authorized service shops had) it's what most of the older B&O service manuals
are based on.

Martin

Re: Beomaster 2000 recap - What do I need?

Stoney3K — Tue, 23 Feb 2010 16:22:56 GMT

Dillen:

So, basically, what you want is a list of which components you need to replace,
how to do it and with what, which instruments to use and what adjustments to make to
repair this Beomaster that was struck by a lightning ?
Sounds easy enough. - Not.

(...)

I'm an electrical engineer and have already managed to save this Beomaster from the scrap yard. The only component that actually seemed to suffer was the tuner section -- probably because our aerial cable at that point took most of the damage (we have a MX5500 which also needed the tuner replaced, but works fine for 4 years straight since now). Upon powering, the BM2000 showed a defect of AF leaking through the tuner onto the outputs, regardless of program selected.

Disconnecting the tuner at the AF outputs (board 1) made a good temporary fix, but I want to have this unit back in fully working order. The 4066's used for program selection may be faulty, but they're pretty easy to replace and might be a good thing to do if I want to be certain, since they were directly in the AF signal path.

I already have the service manual (and can find out which caps are electrolytic and may need replacement first easily), but I can't do a full readjustment from scratch. Any work under 2MHz is no problem, but I don't have very specific tools like a radio frequency scope or FM sweep generator if the need arises to rework the tuner. I haven't changed the adjustments, but if any capacitors are changed or if any inductors or transistors are toast, the whole RF setting may be out of whack and it might need adjustment from scratch.

I was just looking for a list of caps that might need replacement the most (first guess, electrolytic and tantalum power filtering or decoupling caps in the uF range). I know what components do what, and what components I need to stay away from for my own safety or the Beomaster's. Mainly the very big toroidal thing with the mains lead attached, although the 30V power rails can pack a punch too. ;)

Obviously, I can replace everything, since even most IC's and transistors for the BM2000 are still in production. But that would be kind of pointless and I'd be better off buying a new unit.

Re: Beomaster 2000 recap - What do I need?

Dillen — Tue, 23 Feb 2010 15:19:57 GMT

Don't get me wrong - but;

- You don't know which caps to replace
- You don't know what their values are
- You don't know which components that are most prone to failure by aging
- You don't know which components that suffer the most in a lightning strike (usually not caps)
- You don't know if you have the tools and instruments needed to do whatever it is, you want to do.

but you DO know that you don't want a kit because you have a good
electronic supplier just around the corner.

So, basically, what you want is a list of which components you need to replace,
how to do it and with what, which instruments to use and what adjustments to make to
repair this Beomaster that was struck by a lightning ?
Sounds easy enough. - Not.

We can guide you a long way and we would enjoy doing so, but we cannot
provide you with an electronic education.
I suggest you read the service manual, it lists all adjustments and any
electronics repairer will know exactly what to use and where.
It also gives you the whole schematic diagram, from which you can see which
components do what and you can then tell right away which ones are prone to failure
do to eventual overvoltage and/or aging.
If the service manual makes no sense to you, I strongly suggest you leave it to someone
with the skills needed. It will be the best and cheapest solution in the long run.

And to avoid any misunderstandings; No cap kit is available for this model
so I am not trying to talk you into buying one.
The kits weren't put together with lightning strikes in mind either. That's
some of the nastier things to repair with potential internal scars to
components that will only show under certain, usually unknown, conditions.

Sorry if this reply doesn't contain what you expected or wanted but I'm afraid you will
have to convince me a little better that you are fit for this task before I will tell you to
go ahead and put your hands into the Beomaster.
Mainly for your own safety but also for that of the Beomaster.

Martin

Beomaster 2000 recap - What do I need?

Stoney3K — Tue, 23 Feb 2010 14:29:52 GMT

I'm getting ready to give my BM2000 (291x) a good cleaning, and replace some worn capacitors in the process.

Now, the question is, which capactors really need replacing for such an old unit (1983), and, what are their values? I don't need a retail address for a kit, since I can get any capacitor from my wholesale supplier. I'm going to replace all of the capacitors in the tuner section, since they were probably the first to suffer during the lightning damage.

Furthermore, what kind of tools do I need? I've got a basic electronics lab setup (soldering iron, twin lab power supply, oscilloscope, DMM), but I'm not sure if I need additional equipment to adjust the system. Do I need a HF signal generator and analyzer for the tuner section? I haven't changed any adjustments in the meantime.

Adjusting the AF section should pose little problems, since I've got plenty of signal sources (Beocord, Beogram, CD/line) to put that part through its paces.