07-10-2021, 07:43 AM
Hello,
I would appreciate your advice again.
After I changed the 3 Plessy electrolytic capacitors the radio started to pick up 1-2 stations on each band, although the sound is really faint, and the volume adjustment doesn't seem to do anything. I can clearly make out that this is a radio station and human speach, but it's to faint to make out which station etc. The tone adjustment changes the sound distinctively, so I would risk saying it works. In laymans terms I would say that the sound isn't amplified at all similarly to a record player generating sound purely from a needle as opposed to the desired loud output on the speakers. What I can only describe in laymans terms, I hope you will be able to help me translating into the techincal jargon and actions.
I managed to measure voltages across the transistors. My multimeter is that of a very basic variety, so just for comparison it reads 0.0000mV when probes are in contact, and it picks up around 9.6V from the new PP9 battery. The measurements are as follows (I wil go by the Bush's service Sheet naming, the correct measurements from there are in brackets).
Transistor E B C
-------------------------------------------------------------------------
TR1 OC44 1.2V (1V) 1.3V (1.0V) 7.2V (6.4V)
-------------------------------------------------------------------------
TR2 OC45 0.18V (0.25V) 0.33V (0.35V) 8.0V (7.2V)
-------------------------------------------------------------------------
TR3 OC45 0.42V (0.45V) 0.6V (0.6V) 7.4V (7.0V)
-------------------------------------------------------------------------
TR4 OC71 0.12V (1.0V) 1.3V (1.1V) 1.7V (1.5V)
-------------------------------------------------------------------------
TR5 OC81D 1.7V (1.3V) 1.5V (1.5V) 8.8V (8.3V)
-------------------------------------------------------------------------
TR6 OC81 0.03V (0V) 0.18V (0.2V) 9.6V (9.0V)
-------------------------------------------------------------------------
TR7 OC81 0.02 V (0V) 0.2V (0.2V) 9.6V (9.0V)
Some of the readings are high, some are slightly low, I would really appreciate your comments on this one.
I also had a read of a simillar thread in this forum and I found this post:
Should I go with this advice and carry on replacing capacitors? I had replaced C23,C22 and C27, but I didn't touch C21, C25 or C10?
After reading through the thread I had also checked whether the Long/Medium switch operates any better with the contacts being pressed in lightly, but it doesn't change a thing.
Many thanks,
TinaRotator
I would appreciate your advice again.
After I changed the 3 Plessy electrolytic capacitors the radio started to pick up 1-2 stations on each band, although the sound is really faint, and the volume adjustment doesn't seem to do anything. I can clearly make out that this is a radio station and human speach, but it's to faint to make out which station etc. The tone adjustment changes the sound distinctively, so I would risk saying it works. In laymans terms I would say that the sound isn't amplified at all similarly to a record player generating sound purely from a needle as opposed to the desired loud output on the speakers. What I can only describe in laymans terms, I hope you will be able to help me translating into the techincal jargon and actions.
I managed to measure voltages across the transistors. My multimeter is that of a very basic variety, so just for comparison it reads 0.0000mV when probes are in contact, and it picks up around 9.6V from the new PP9 battery. The measurements are as follows (I wil go by the Bush's service Sheet naming, the correct measurements from there are in brackets).
Transistor E B C
-------------------------------------------------------------------------
TR1 OC44 1.2V (1V) 1.3V (1.0V) 7.2V (6.4V)
-------------------------------------------------------------------------
TR2 OC45 0.18V (0.25V) 0.33V (0.35V) 8.0V (7.2V)
-------------------------------------------------------------------------
TR3 OC45 0.42V (0.45V) 0.6V (0.6V) 7.4V (7.0V)
-------------------------------------------------------------------------
TR4 OC71 0.12V (1.0V) 1.3V (1.1V) 1.7V (1.5V)
-------------------------------------------------------------------------
TR5 OC81D 1.7V (1.3V) 1.5V (1.5V) 8.8V (8.3V)
-------------------------------------------------------------------------
TR6 OC81 0.03V (0V) 0.18V (0.2V) 9.6V (9.0V)
-------------------------------------------------------------------------
TR7 OC81 0.02 V (0V) 0.2V (0.2V) 9.6V (9.0V)
Some of the readings are high, some are slightly low, I would really appreciate your comments on this one.
I also had a read of a simillar thread in this forum and I found this post:
(30-11-2013, 07:56 PM)Refugee Wrote: The first port of call for a gain fault is the red/black capacitor C22 and C10.
For distorted loud audio C27 first then C21.
For tinny or weak audio C23 and C25.
You will be able to see that C22 and C10 keep the power to the receiver part of the set clean of AC and leakage of the received signal. Any signal lost here does not get to the detector diode.
C21 will make the DC voltages on TR4 bad and part of the audio will get distorter off so that it never gets to the speaker and this will make the set sound awful. C27 will cause buzzing and screeching that can be intermittent or constant that gets worse as the battery ages.
C23 and C25 stop the audio from getting onto the resistors that have to be there to regulate the voltages on TR4 and TR5 the effect of one of these going faulty will start with poor bass and get worse. Faults with these capacitors will be amplified by the transistors.
Most of the buzzing will be from power cables close by and once the gain of the receiver part of the set is restored it should be drowned out by the stations you listen to.
Should I go with this advice and carry on replacing capacitors? I had replaced C23,C22 and C27, but I didn't touch C21, C25 or C10?
After reading through the thread I had also checked whether the Long/Medium switch operates any better with the contacts being pressed in lightly, but it doesn't change a thing.
Many thanks,
TinaRotator
