Teleton F2000 AM/FM Receiver with low volume

[DMcMahon]

As per my other Teleton F2000 Thread this second one has low volume.

https://www.vintage-radio.net/forum/...d.php?t=186331

Condition wise not bad, front panel lettering better than than my first F2000 but the woodwork is not as nice looking.

None of the scale illumination lamps light up, so the LES bulbs that were supplied will come in very useful.

Forgot to mention previously that believe the F2000 was part of an F2000 component system including speakers and record deck.

Evidently this unit had previously been modified with a RIAA pre-amplifier add on but the mod has been removed. I assume this was to make it useable with a magnetic cartridge record deck, believe the original deck would have had a ceramic cartridge.

Initial test results very similar to the other unit but with lower volume.

Same standing hum level on both channels and the right channel also not working. Am sure my signal lead is good and have tried 3 pairs of headphones, so it looks like the right channel is dead on both units (with signal connected to the tape input) which seems strange.

When the input selector is switched away from the tape position there is low level breakthrough of the tape signal but nowhere near as noticeable as the other unit.

David

[DMcMahon]

Opened up and removed the RIAA amp add on, to make it easier for any subsequent fault finding.

None of the 4 scale illumination lamps previously worked, found only 2 fitted but have not yet been able to remove them (assume they are blown). The DC supply measured OK at -26.4V

David

[DMcMahon]

As per my other F2000 Thread the right channel is now working after correcting the input/output connections on my Phono to DIN cable. The right channel is very similar low volume as per the left channel.

David

[martinhog]

Interested to see how you get on with this one. Seem to recall the mains switch on the negative side on these models ?

[DMcMahon]

Using good test data I obtained from my working F2000 I checked out the 4 output transistors. Their DC voltages all checked out OK possibly indicating that the these transistors are OK.

Inline with the operational tests the collector outputs were well down in amplitude (maybe around 1/10th) but otherwise looked OK. However the base drive signals on 2 of the transistors (1 on each channel I think) were bad with only -ve going signal waveform.

Looking at the output of the pre-amp board 1 channel is missing (maybe left), this does not make much sense because both channels are working (albeit with low volume) with same volume and both controllable by the volume control.

Very unsure what this all means, looks like 2 separate problems but it is confusing because both channels have the same reduced volume symptom.

More checks required.

David

[DMcMahon]

Checked all 4 of the output transistors to be sure they are OK, all junctions checked good.

Found that disconnecting the left channel output of the pre-amp board into the output transformer board killed the left channel, which indicated that there was some signal on the left channel even though could not see any signal, scoping the left signal when disconnected showed a signal around 1/20 of the good right channel signal.

Swapped over the left and right channel input wires at the output transformer board resulted in the left channel working fine (with right pre-amp signal), so this confirmed that the right channel has a fault.

Traced the right channel fault to a dead 10uF electrolytic that couples the pre amp output (Q404 collector) into the base of transistor Q502, it only measured 66pF.

Replacing the capacitor has fixed the right channel.

To fix the left channel fault requires the pre-amp board to be removed which is a real nuisance.

David