Hi Menahem,

I have plenty of 4148's but not the other type. Assuming they are cheap to post can I buy 2 from you? please send a PM with a price.

Thanks

PM sent!

And BTW, I just found this off a Tech database:

Plays only 30cm records – Arm does not stop for 17cm

Replace capacitors C12 (2.2µF) and C16 (0.1µF) in detection arm unit.

Check to see if this is applicable to your type - check the ESR's of the caps.

Just scanned and uploaded the manual for the Beogram 4002 and 6000. This one covers the following models:

T5514, 5515, 5524 + 5527.

Full circuit diagrams and some additional service tips at end. Due to our manuals being downloaded and then sold on eBay, this is, as with all our new manuals, stamped and copy protected. I realise there are ways around this but it will take a bit more effort!

I have now received the diode from Yachadem, Thanks.

To be certain, before I replace, The black stripe is the cathode? and goes to the collector of the transistor? in the circuit snippet above.

Yes, the black stripe is the cathode.

Yes, assuming that the diagram is correct (and I would double check it against the existing diode on the PCB), the cathode goes to the collector.

Menahem

Diode replaced, problem solved. Lets hope it stays that way.

Thank you everyone!😁

Let me try to revive an old thread...

My Beogram is a type 5527 and i've just downloaded the 'new' service manual that Peter kindly uploaded.

Where to start..... Problem is that the arm will lower at the 12" position even with no LP on the platter.

I traced bad wiring to the photocell in the arm - that was replaced. All of the small tantalum beads were replaced just for peace of mind (all the correct polarity)

Problem continues... I got the 'scope out to see what was going on. The photocell is giving an output.

Connected the scope up to compare to the diagrams under 'Detector arm circuit' listed on page 7.4 in the service manual.

Measuring at the base of TR3, the waveform just appears as noise. Stimulating the photocell with the platter doesn't appear to do anything.

Next, onto measuring the collector. I get approx 3v instead of the specified 4 when in a steady state. On stimulation, the waveform looks similar to the diagram (with more noise), but the waveform stays between 2.5 and 3.5v. If I shine a very bright light onto the platter, it the wave will reach 0v at the trough, and go slightly past 6v at peak. The arm still lowered though even with a bright light there.

I didn't have chance to measure the base of TR4 yet... I had to put all of the equipment away before I had the chance.

The resistors in that part of the circuit all measure within spec, and the supply +21v looks nice and clean.

I did change TR3 to a BC549 (similar spec to original), which yielded neared to 4v at the collector, but that was about all.

I'll try to have another look at it tomorrow, but if anyone can suggest anything in the meantime, I would appreciate it.

Ben,

I take it the sensor arm lamp is shining OK on the record and is of the correct wattage ?
All aluminum surfaces installed ?
Given those;
- Check that the lamp is sitting correctly, with its filament
right above the focus lens and as close to it as possible.
- Check the grounding connection to the carriage.
- The lamp can have degarded. Its light output degrades with age.

The sensor cell gives only a few hundreds of a volt, not easy to measure without
disturbing the signal.
Instead, I recommend you measure at the base of 1TR4 where the signal amplitude
(reflections from the platter ribs) should be about 1 Volt offset to apprx 20V DC.

Martin

Hi Martin,

The arm lamp is correct, but is old, so maybe degraded.

When measuring the photocell output before the decoupling capacitor (2.2uf), I can see where the ribs on the platter are, but after the capacitor, it all just becomes too noisy.

I didn't have the aluminium surfaced installed when I was measuring with the oscilloscope, but they have been installed previously, and the arm still lowered.

I'll get all of the gear back out tomorrow and have a look at TR4 - Will take a picture of the display on my 'scope and upload it.

Thanks,

Ben

Ok, so I tried to measure the base of 1TR4, I would get only 21V steady. 1TR4 tested to be short circuit between base and emitter. This was replaced and here is the image as viewed at the base of the new 1TR4... looks pretty close to the one in the workshop manual.

Peak to peak, its approx 1V with the bright light shining on the platter, without its approx 800mV.

The deck still was lowering the arm though...

I soldered a wire to the base of 1TR6, so I could reassemble the deck and observe the waveform, and hey presto, the arm continued over the platter! I placed an LP on the deck, and the arm would lower.

There must have been a dry joint on transistor TR6 that was fixed when soldering on my flying lead.

I still need to sort out the lamp in the detector arm though... I can't always have a desk lamp pointed at the deck! What is the specification of this? In the manual, it just says 'Lamp 6V'.