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So should I measure volt from the resistor from tr49 emmiter and with ohm law to adjust the current?
Sounds right. But the idle current is not the problem in your case.
You will have to find and correct the problem first.Martin
The 250-ohm trimmer and TR45 governs how much no load bias is applied to each base. It is mounted on the heat sink to sense temperature and also adjust the bias. It’s possible that transister is bad or the adjustment is too high. The circuit calls for a BC311 and since the bias is not separately adjustable for its BC310 mate its possible that your BC161 is a poor match. Sorry, but its been too many years since I worked on one of these.
TR45 is usually a small BC183 or such.
TR44/47 does not have to be matched, as they see the same current flow regardless (more or less – in a working circuit).
Even the output transistors doesn’t have to be exactly matched, really.
The above also goes for them, and their emitter resistors will compensate a little for minor differences in hFe as well.But the problem in this case is of a different scale.
A DC reading in a “controlled” environment (variac and a couple of multimeters) on the output rail would tell something. As would DC-readings
on the driver transistors.Replacing components just to see if they burn, will not help in any way.
You need to find out what is really going on.Martin
The base of TR45 should be adjusted to 27.2
– No.
You adjust the idle current to a given current flow at the output stage emitter resistors as stated and shown in the manual.
The voltages stated in the schematics are not for alignment purposes.
They are merely to help diagnosing in that you can see if a voltage is far off.In a working circuit, the voltage(s) stated at TR45 will change with temperature, as will the voltages stated later in the circuit, because that is what
the circuit is built to do.
TR45 measures the temperature on the cooling fin and adjusts the final
output stages accordingly.
A transistors amplification increases with temperature, so if nothing grabs
and controls it, it would run astray until something starts burning.
That’s also why idle currents always are to be set with the amp (output stage/cooling fins) at room temp.Martin
Don’t get me wrong, it may sound harsh but I mean this in the best of ways when I say that
I have a feeling that you will not be the right person to do this repair.
Your methods will only bring more headache, and it appears your electronic education and experience is limited. Right?Every educated electronic technician will know what the emitter resistors are and how to
measure idle currents.
The manual may state a mA figure, which is and refers to the actual current,
but a brief look at the emitter resistors value and a little bit of Ohms law will
allow you to measure the current through a resistor as a voltage across it, and
as an added bonus you can measure it without disturbing the circuit by lifting components.
You only need to take the top cover off to measure and adjust.And I wasn’t referring to the output series capacitors. I was referring to the capacitors
in the output stage itself, as that is where the problem is.
They must be replaced, and it’s good advice to never fit low-ESR types in a circuit like this.Output stages like this can give even trained tech people a good run for their money.
Martin
Stop swapping components. It will only up the risk of more trouble.
The idle current settings and measuring ponts are given in the service manual.
It’s a voltage measured across the emitter resistors with no speakers attached and volume at zero (hence the term idle current).
7,5 mV if I remember correctly – see the manual.
But if a transistor burns, there is something else wrong – the burning transistor is not the reason.
And if you replace one or more semiconductors in an output stage, you MUST set the idle current again at first power up.
Bring the Beomaster up slowly on a variac while monitoring the idle current – power down immediately if something looks wrong.Did you replace the electrolytic capacitors in the output stage? If you did, did you fit low-ESR types? You shouldn’t, as that will often be asking for trouble.
Martin
Where are you?
Martin
Actually, both are correct.
Early Beocenter 3300s have the platter from Beogram 2200/2400 etc.
Later the one from Beogram 2202/2402 was fitted, – and it has the extra black weight strip
underneath.
The later and heavier one has marginally better specs.Martin
It’s not the same.
It’s higher. And if a tonearm lift is fitted, there will be a cutout for it as well.Martin
Bad, or badly seated, ribbon cable?
Martin
Can you tell if the disc is scraping on the alu tray?
I have noticed, in some decks, a little more height is needed for the suspension rubbers in order for the disc to fully clear the tray.
If so, you can fit a thin washer (0,5mm or so) under the rubber parts, between the
rubber parts and the drive base chassis to lift the (rubbers and) drive slightly with respect to the alu tray.
This will also solve the noise issue, if it’s the clamp scraping on its metal bracket as it will also be lifted by this.New suspension parts, that I am currently working on, will be corrected for this.
Martin
Does the lower display get any power?
If it gets power, does it get any data?Martin
It’s all down to alignments and which tape types the deck has been calibrated for.
Tapes of different brand or types can be very different indeed.A couple of hours work, usually, and some instrumentation etc. is needed, but it is
possible to calibrate the Beocord to whatever tape you prefer to use.
(That’s what Beocord 9000 can do at a touch of a button, strictly speaking).Martin
Sorry to spoil the fun, but anti-static mats are absolutely NO-GO on any Beogram.
First; Due to the thickness of the mat, the needle tracking angle will be wrong.
Second; Because the presence of a record is often determined by either optical
sensors or weight, many Beogram models will think there is a record on the
platter – even if it’s merely the mat, and they will gladly try to play it…
A needle lowered onto a rotating felt mat… Ouch, – bye needle.Third; One is never needed, if the deck is in good working order.
You could run a grounding wire from a bolt of the main bearing (note its position or you
will have to realign the bearing) to somewhere on the main metal chassis.Martin
It’s difficult to find cable of the same type as the original.
So far I have managed with what I could find in the dungeons from scrapped units and leftovers collected over decades from closed repairshops, but perhaps Steve can give us an idea?The original black color seems to vary a little. If this is because of age and sunlight or because the original production spanned several paint batches I cannot say.
A not-to-reflective but not exactly flat silk black either, should be close.Martin
Nice job – but as I see it, there is no longer any shielding between the two signal leads.
There is quite an amount of amplification to whatever comes out of that cable, so even
the tiny amount of transfer caused by capacitive coupling between the two long parallel
leads close together could cause the channels to mix a little (loss of channel separation).
It’s marginal – that’s correct, but the old cable was in fact of better quality in this respect.The new cable would be better suited for balanced signals, really, – stage gear, microphones with long leads and the likes.
And you are absolutely right about the two grounds.
Martin
Failing switch.
Give it a shot of contact cleaner and work it a dozen times.Martin
Carefully remove the locking washer on the top of the spool. It has a slit so is usually not difficult to remove.
Then take off the spool – note the small anti-vibration insert. It’s a tiny round bronze plate, wedged up against the spindle – easily lost.
While in there, I suggest you clean the spindle and inside of the spool off old grease and add a small amount of fresh white lithium grease.Martin
Yes, the magnet has come lose.
You must take off the the reel table and glue the magnet back onto it.Martin
I agree.
Martin
The reel tables carry the spindles with tridents that grips into the spools with the tape.
Martin
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