Hello Everyone

I have an Australian HMV Rhapsody Radiogram from 1969...that has a weak channel...quieter than the other and less responsive to the tone control.

Radio works, (AM only) and the BSR Turntable also works well
It hums a lot - however I understand this was always a thing on this model.

I'm attempting a repair for my daughter...would like to keep the repair original if possible however I've become aware that it uses Australian Vintage Transistors, which are no longer obtainable...(if that is the problem!) so would then need a plan B


Wondered if anyone has knowledge of working on a Rhapsody and ask if anyone has had a similar issue and could advise what to look for.

At the moment the the chassis is removed and access is easy to work on and test/repair...so far no apparent burning, bulging, no obvious issue with soldered connections.

So far I've identified the section of the circuit board which has the weak channel (only one circuit board and easy to see the different amplifier channel and radio circuit sections)

I have a few Electrolytic Caps I could change..but thought it best to ask first for anyone's experience on this unit with regards to how to approach this issue.
Noted there are a couple of ELNA Electrolytic Caps used in the Amplifier

I do have the Schematic and Service Manual...(have sent to admin- to be added to this thread)

Thanks in Advance for any responders!

HMW Rhapsody T8-49 Circuit Diagram

All transistors would still be available, or suitable substitutes.
More likely electrolytics have dried up.
Especially the power supply and audio coupling electo's
Need to look at circuit before making any guesses.
Should not be too hard to repair/restore.
No manufacturers would have let out a model with hum problems, so its obviously had problems for a long time.
JJ

Hello Johnny
Thankyou for your reply!

Good news !
Just finished replacing all the electrolytics and the both channels are now working !
A couple of 'Ducon; Caps were found bulging at the base.

For the record here are the Transistors used - its a credit that they are still working!

SE1001
SE4010
AX1108
OC987
OC988

I still have a lot of hum...not sure why that is.

Also noticed the AM radio works well at start up but then after a while sensitivity reduces and gets replaced with more noise and only the strongest station is then audible.

Not sure if I should continue to replace all other Caps...is it worth it ?

Cheers

If you can hear hum with volume control turned right down it would indicate a power supply problem.
Or something is drawing too much current and the power supply can't cope.
However if something and particularly the output stages is drawing too much current then distortion would also result.
You did not mention distortion so check power supply.
Having changed all the electro's in the power supply the next step would be to measure the actual supply rails.
JJ

Thanks Johnny

Had another quick look after dinner at this ...Right Channel has quite a lot more hum than the left ...and sometimes when turning volume Pot - reducing the volume to getting near zero - the Right Speaker starts sounding like a subwoofer/oscillating the hum..you can see the speaker membrane vibrating !

This only happens sometimes - but consistent is the louder hum in the right Channel speaker.

Clearly I'm not there yet!

Right channel motorboating intermittently.

Document uploaded.

Thankyou Brad !

BBTV - Thankyou ..its a new one for me... wondering what the cause is... !

A couple of comments after looking at circuit.
You have changed C25 2000uF?
And changed C26,C34 marked as 80μF, but 100μF would do.
And wired the right way around? Very important.
Also are the speakers original, because they need to be as designed 27 ohms.
A low impedance speaker could cause your problem.
JJ

Thanks for replying Johnny

Yes replaced C25, C26, C34 - C26, and C34 were bulging at the base.

I believe I have connected them correctly following the schematic

The speakers are original and as you say 27 ohms ...thats a new impedance for speakers for me! I also tested the 27ohm original speakers by connecting to the other channel see if they were at fault but no..the same result...it def is humming badly and consistently coming from right channel

I should say that after changing the electrolytics....the symptoms def didnt get worse.
The bad hum was there in the left channel to begin with..so whatever Ive done so far has not affected that for better or for worse.

EDIT
There a few anomalies wrt to the schematic and what was actually on the board:

C33 Was replaced (left Channel) - however in the schematic it is shown as a non electrolytic 15μF, However in reality it was a 50μF Electrolytic ....
For some reason IDKW there is no corresponding Cap on the Right Channel Circuit...the schematic and actual board agree - just wonder why !?

Also
C28 and C29 are listed as 0.22μF Ceramic Caps....though they were actually 0.5μF Polyester.

C33 is just a bypass/filter and even though situated in the left channel area also connects to the same positive supply rail.
Suspect output stage drawing too much current, possibly a leaky transistor.
What is the centre voltage of this complementary symmetry output stage left and right.
Ie, the voltage on the positive of C34 and the positive of C26.
Both should be exactly 14.5 volts, at no volume and full volume.
JJ

I didn't see any mention of checking C14 which should be 50μF . C33 looks like 0.15μF on the diagram, although 50μF won't hurt.

Does adjusting the tone, balance, or volume have any effect on the motorboating or hum?

There's a feedback mechanism in each channel via the tone control. Check C22/C31 (470p) and C24/C32 (22n).

The first amplifier stage is surrounded by high-value resistors which could have drifted over the years to be even higher or open-circuit.

Lots to check yet!

Right - I have to apologise for a mistake !

The Motorboating ....it was my bad !

To replace the 6.4μF Electrolytics for each channel on the Balance Control Pot...I inadvertently married two 33μF in Parallel instead of 2x 3.3μF in Parallel (to give me 6.6uF) ....thought they were 3.3μF but they were 33μF !

Luckily no damage done !

Motorboating now not occurring.!

I had started to wonder - as when I was adjusting the balance the motorboating effect started to occur.

The hum is still there...but slightly less in the Right Channel

Thanks Johnny - Results of testing:
The Voltage at C34 and C26 checks out a 13.4 Volts (both the same at both ends of Volume)...I measured the rail and its 26.8Volts ...a bit less than advertised in the Manual (29V)

Hello Robbbert Thankyou for your reply
C33 in reality was/is 50uF..and I have replaced that as it was also an Electrolytic (unlike what is shown in the schematic) also as I mentioned previously this Filtering/Bypass Cap (C33) (as identified by Joihnny) is only on the left channel not on the right ..there is space on the board for one...though its not shown in the Schematic either.

Adjusting the balance volume and tone does not seem to affect the hum much at all. You can hear it at Zero Volume for example.

I will check/replace C22/C31 & C24/C32

and also I have not yet checked the resistors as you mentioned...

One thing I cleaned tonight was the the two mono input jack sockets......they looked grubby and if the contacts arent clean I'm sure this could affect the signal.

I noted the construction of the Chassis has 6volt AC lamps and that those wires intermingle with signal wires...in fact signal wires are routed all around the transformer...I wonder how much interefernce is being transfered into the signal

Radio is acting up still - whereby it works well when power has been removed for a while and its first turned on - very sensitive and selective...but as time goes on good signal is replaced with more noise and loss of signal..not drifting off the station as such...just losing overall signal...its not the amplifier as I have managed to utilise the Din like socket of the turntable and input audio from an old phone..which plays fine over a period of time.

Yep got things to do still!

Radio problem may be caused by faulty C6, 10μF. AGC line filter cap.
I'm not sure you are referring to mains "hum" or "buzz" from bad lead dress or open circuit earth connection.
The volume pots themselves give a fair bit of trouble, particularly if they have been sprayed with WD40 in its lifetime.
You may have to remove and carefully meter out. Of course taped pots are made of unobtainium.
Does the buzz or hum disappear when inputs shorted to deck(earth). ie, test points K and F.
JJ

Hello Johnny thank for your reply

I changed out C6 ..it was old ELNA can....now radio seems even more sensitive....its on test now will see how it goes.

I connected K and F together and then shorted to ground ....no difference in hum.

However I did not short the pins individually to ground one at a time - do you think thats worth doing to see if there is any difference between the channels?

The Volume pot was a bit scratchy at near zero volume....took a while but with some jaycar Electrical clean & lube (I hope its better for the pot than WD40) - finally the scratchiness was gone.

Cheers