Ninni
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The 7400 is a quad NAND gate. Connecting three pins together isn’t uncommon. You do it when you use one gate as an inverter.
Have you tried to connect the ground lead to the central pin (pin 3) on the DIN connector? Or to the DIN connector shield?
Does it play, sounding normally, when you switch it on?
Is there a trimmer for idle current?
It’s probably to prevent external loads from affecting normal operation of the internal power amp (and speakers connected to it).
So the problem is that it doesn’t activate the switch, to start the motor.
A difficulty with this mecanism is that you can’t normallly watch it operate, as it’s on the underside of the deck.
You say nothing happens. Have you tried pressing the button gently and keeping it depressed for a second or so?
Does the platter start spinning when you press the button?I did add a simple FM antenna to get better reception. Just two wires out of the plug. The other bands require another antenna, though.
The smallest belt is for detecting that the take-up spool rotates. This is for detecting end-of-tape and turning off the transport when the tape ends. The belt usually drives a rotating magnet and a hall-element (that detects the magnetism). So if this belt is no more, the deck always thinks that the tape has ended.
Have you checked that the mechanism belts are OK? This will happen if the drive belt has failed.
The idle current should be measured by unplugging the supply lead to the power amplifier for the channel to be measured and inserting an ammeter in between. This should read 100 mA, if I recall correctly. There is a warm-up time for taking the reading. Everything is in the service manual.
Thanks for the TIP, Glitch. I compared the data sheets and these seem promising and are available at decent prices.
Yes, but which modern transistor is a working equivalent? These are Darlington transistors, if you weren’t aware of that.
The output transistors are screwed into an aluminum heatsink, the normal way (see picture).
I need replacement transistors to repair this Beomaster.
The Beomaster was working normally. I was going to measure the idle current and one output transistor suddenly failed. Before this happened, the heatsink did not get warm, so I think the idle current was actually too low and definitely too high.
I think different models of belts are made with different kind of rubber and therefore degrade differently. The round belts for the old Beograms seem to last forever, for instance.
You shouldn’t run the full range signal from the amplifier into the tweeter terminals, unless the loudspeaker has built-in crossover filter for the tweeter. If it has separate connectors for the high and low register, that indicates the contrary. Then it’s probably designed for active filters and biamping.
Maybe the service manual for the Beomaster 901 can be used? Aren’t the amplifier sections identical? I’m currently working on a BM 901, by the way.
Hi again, It turned out that the BC8000 did not have a “TR9” issue – my issue was also a little different. It could Play, REW and stop by command but when selecting FF it stayed in FF eventhough pushing Stop. Measuring around on board 4 showed correct electrical signals. It turned out that the FF solenoide was half stuck staying in outer position. Lubricating the rod inside solved the issue. Finally everything works
/PindsenSimilar to the issue I had with my Beocord 5000. Fixed by cleaning and lubricating.
Unfortunately, there is still a slight problem. Playback doesn’t quite start when the deck hasn’t been used for a while. It does work if you do a couple of retries and after that it works every time.
It’s clearly something that doesn’t move quite as freely as it should. I’ll have to examine the mechanism again. Have any of you experience with lubricating this mechanism?
After some more troubleshooting I found the problem. The lever from the wind solenoid was gummed up. It’s supposed to return by spring force but didn’t.
I removed it, cleaned the shaft and added a drop of oil. After reassembly, the tape transport works as it should.
I must say, this Beocord is the most service-friendly tape recorder I have come across. The service manual leaves something to be desired, though.
In the first picture, my assistant points to the lever in question.
In the second picture, you see the entire lever. It’s the one on top of the gear. (wind solenoid removed)
