Racal RA7915 main receiver board schematic needed

[Jeff]

Hi,
I need a good quality A3 size copy of the main receiver board schematic in
an RA7915 HF receiver. The schematic is I believe the "mark2" version of the
#2270 PCB, where R45 has been added to pin 12 of ML2. This resistor is not
present there in the "mark1" circuit.

I have an A4 size copy (of a copy, I think) but it is very hard to read due
to the high density / small size, and some component values are illegible.
Any help appreciated. Am happy to pay for expenses and postage costs.
regards,
JEFF
ZL3TNV
Christchurch, NZ.

 

[budgie]

Hi,
I need a good quality A3 size copy of the main receiver board schematic in
an RA7915 HF receiver. The schematic is I believe the "mark2" version of the
#2270 PCB, where R45 has been added to pin 12 of ML2. This resistor is not
present there in the "mark1" circuit.

I have an A4 size copy (of a copy, I think) but it is very hard to read due
to the high density / small size, and some component values are illegible.
Any help appreciated. Am happy to pay for expenses and postage costs.

Jeff, was that one sent over to you from VK6? I recall putting you on to VK6UK
regarding sourcing one.

I don't have a cct, but I do have the sister of that unit (if it is as above)
and if you need a value I could peer into mine.

 

[Jeff]

Yes, thats right, VK6UK. Its been a while, and Id deleted all my emails
pertaining, so had no idea of names, email addresses, etc, anymore.
Im refurbishing some of the receiver at present. Got some (A4) mark2
schematics from someone else (cant remember). The receiver I have is a
composite, i.e mark2 front end and mainboard, with the mark 1 (no PLL) oven
oscillator.
With a push, I can work the values / locations out, but its a hassle, hence
the request.
JEFF

 

[John Crighton]

Hi,
I need a good quality A3 size copy of the main receiver board schematic in
an RA7915 HF receiver. The schematic is I believe the "mark2" version of the
#2270 PCB, where R45 has been added to pin 12 of ML2. This resistor is not
present there in the "mark1" circuit.

I have an A4 size copy (of a copy, I think) but it is very hard to read due
to the high density / small size, and some component values are illegible.
Any help appreciated. Am happy to pay for expenses and postage costs.
regards,
JEFF
ZL3TNV
Christchurch, NZ.

Hello Jeff,
have a look here
http://www.vk2bv.org/museum/
If that doesn't work google "kurrajong radio museum"
Under Radio Sets
scroll down to RA7915

OK, I know that doesn't help you but others can see
what you are talking about.

I did help out Ian O'Toole with a circuit for the old
6 channel oven oscillator module a couple of years
ago. There is a good chance he may have collected
the other circuits by now. E-mail Ian and find out.

Back in the early 1970's at Racal, North Ryde, Sydney.
I used to sympathise with my workmate Bill, as he
struggled to test and repair this receiver in a small
screened room about 6 foot cubed. Inside the factory
in the height of summer, he was in an oven.
Why were they tested in a screened room? Because
the radio barely made specifications. Failed the sensitivity
specification above 8Mhz. The test sheet had to be
signed by the managing director as well as the test
technician so the receivers could go out the door not
meeting specification. I am just trying to remember
who the big fat managing director was. My memory
is letting me down. Bruce Godard! That was it!
Godard, what a good name for a big boss. Heh heh heh....

I remember my mate struggling to get a batch of these
sets out the door. Some oven oscillator modules
when plugged into the receiver, gave the Rx better
signal to noise figures than with other oscillator modules.
So the better oven oscillators were fitted to the problem
Rx's where sensitivity was a problem. That is sets with
channels above 8Mhz. Same with the main boards,
they were chosen like that also. A receiver that went
out the door with low frequency channels probably
just made specification. If higher frequency channels,
8Mhz or above, were to be fitted later, the Rx would be
struggling. These were the tricks of the test department
when one was pushed to get one's quota done.

I remember an engineer stating that all the modules
for all of a batch of six radios should be able to be
thrown up in the air and randomly selected for a
batch of six radios and they should all meet specification.
After this guy spent all day struggling in the screened
room he said to Bill, "Just do your best, Bill." and he
kept well away from then on. heh heh heh.....
You have brought back some funny memories
for me of that crazy workplace; factory romances,
good folk and arseholes. They were all there.

Regards,
John Crighton
Hornsby


PS
Hello Budgie or anyone else,
who may be familiar with an old Codan 4000 transceiver.

When I first switch the power on at the control
unit. The frequency display and LED indicators
flicker slightly, in intensity, for several seconds
in intermittant fashion and then settles down to
normal steady intensity.

I am just checking if this is a quirk of this transceiver
or not before I spend anymore time chasing this
strange behavior.

After switch on, the intensity of the display and
indicator leds vary in normal fashion. When a well lit
room darkens the the display dims as it is supposed to.
I have no previous experience of this transceiver.

Thanks for any info.
JC

 

[Brian Goldsmith]

I need a good quality A3 size copy of the main receiver board schematic
in
an RA7915 HF receiver. The schematic is I believe the "mark2" version of
the
#2270 PCB, where R45 has been added to pin 12 of ML2. This resistor is
not
present there in the "mark1" circuit.

I have an A4 size copy (of a copy, I think) but it is very hard to read
due
to the high density / small size, and some component values are
illegible.
Any help appreciated. Am happy to pay for expenses and postage costs.
regards,
JEFF
ZL3TNV
Christchurch, NZ.

***** Jeff,let me have your address off list,I will send you a
"readable" A3 copy of the 2270 PCB circuit.

Brian Goldsmith.

PS. Remove the obvious to reply. BG.

 

[Jeff]

Thanks for that John. I have been using the receiver, but it slowly died off
over a week. In measuring a random selection of the resistors, was a bit
horrified to see most were well out of tolerance - some by 300%. Oh dear!!
From what you say of the factory, it sounds like it was a lucky dip whether
the customer got a good set (or not), but seeing they were in costal station
service for so long, I guess they werent too bad.
I have some Redifon R499 receivers in use, which is mostly an equivalent
(features wise) to the Racal, but have much better specs. Used for
air-ground and ground-ground for what was the Civil Aviation department in
NZ.
regards,
JEFF

 

[John Crighton]

Thanks for that John. I have been using the receiver, but it slowly died off
over a week. In measuring a random selection of the resistors, was a bit
horrified to see most were well out of tolerance - some by 300%. Oh dear!!
From what you say of the factory, it sounds like it was a lucky dip whether
the customer got a good set (or not), but seeing they were in costal station
service for so long, I guess they werent too bad.
I have some Redifon R499 receivers in use, which is mostly an equivalent
(features wise) to the Racal, but have much better specs. Used for
air-ground and ground-ground for what was the Civil Aviation department in
NZ.
regards,
JEFF

Hello Jeff,
I remember many people complaining about those crappy resistors
but the word from Godard was "Use 'em up."
That was the time when accounting type people were starting to
have more influence than engineers. I complained to one of the
engineers and he just mumbled in his beard. He wasn't happy,
he had been shouted down by management at some stage.

There was a bad attitude in the place to just do as one was told
and to hell with the consequences as suggestions for improving
something were not appreciated. The rot permeated from the
top down. When workers are treated like shit, quality of the
product suffers.

With the crappy resistors, if you have a good desoldering tool,
or are slick with the solder pullet and solder wick. It wont take
long to check them all and replace the bad ones.

Maybe even consider replacing all the crappy resistors. There
was a mixture of the crappy style and better quality types used.
To protect the tracks of the PCB from too much heat, you
could just snip the resistor leads so that the stubby bit of wire
almost drops away from the PCB track/pad. Protect the
tracks of the board rather than trying to remove a shitty
component in one piece.

I worked at a joint that made uninteruptable power supplies,
Mitec. Castle Hill. They had used some brand of crappy little
0.1MFD capacitors that were used as IC decoupling capcitors.
When a UPS came in for repair it was standard practice to
unsolder about 55 of these little caps, fit new ones of a different
brand and then start fault finding the unit. Six times out of ten
the unit came to life after replacing those little caps. They were
bad. Like little time bombs.
The point I am making is, replacing all your crappy resistors
is no big chore once you set your mind to it.

Have Fun,
John Crighton
Hornsby

 

[John Crighton]

I need a good quality A3 size copy of the main receiver board schematic
in
an RA7915 HF receiver. The schematic is I believe the "mark2" version of
the
#2270 PCB, where R45 has been added to pin 12 of ML2. This resistor is
not
present there in the "mark1" circuit.

I have an A4 size copy (of a copy, I think) but it is very hard to read
due
to the high density / small size, and some component values are
illegible.
Any help appreciated. Am happy to pay for expenses and postage costs.
regards,
JEFF
ZL3TNV
Christchurch, NZ.

***** Jeff,let me have your address off list,I will send you a
"readable" A3 copy of the 2270 PCB circuit.

Brian Goldsmith.

PS. Remove the obvious to reply. BG.

Hello Brian,
well done! Jeff will be pleased.
Great to see this sort of thing!
Makes newsnet worthwhile.
Regards,
John Crighton
Hornsby

 

[Jeff]

John,
Just about decided to replace them all. Have enough stock to do this. Have
done similar chore to my Eddystone 940 a long time back, which had the same
type of resistors. Makes a world of difference.
Tantulums and electros may be dodgy too, but will do the resistors first and
see how it goes. I notice there is a mixture of types as you say, and even
some 2% ones I think also.
The pcb tracks look like they could take the rework quite well, not like the
Marconi LCR bridge Ive got, where the tracks lift themselves up, and run
away each time they smell the soldering iron getting close!!!
JEFF

 

[John Crighton]

John,
Just about decided to replace them all. Have enough stock to do this. Have
done similar chore to my Eddystone 940 a long time back, which had the same
type of resistors. Makes a world of difference.
Tantulums and electros may be dodgy too, but will do the resistors first and
see how it goes. I notice there is a mixture of types as you say, and even
some 2% ones I think also.
The pcb tracks look like they could take the rework quite well, not like the
Marconi LCR bridge Ive got, where the tracks lift themselves up, and run
away each time they smell the soldering iron getting close!!!
JEFF

Hello Jeff,
while we were discussing the shitty resistors, I just remembered
the shitty oven oscillator resistors and lousy workmanship
on the oven casting.

I think your set could use the old style oven oscillator with
maybe six D size large crystals as well as a later model
oven oscillator with twelve smaller size crystals.

I want to warn you about the "later model" oven oscillator unit.
The heater transistors, are screwed to the side of the oven
casting. Fair enough, but the casting is very rough and uneven,
the lazy bastards in production would not file it flat. So the
contact between the casting surface, mica washer and flat
pack power transistor BD??? is bad. To make matters
worse, the little brass threaded insert that is pushed into the
casting to take the screw of the power transistor sometimes
stands proud of the casting. Meaning there is a gap between
the power transistor and casting when screwed up. The
thin mica washer can get damged by the proud insert and
not insulate the transistor from the casting. Out the door they
went just like that for other people to fix in the field when
they failed later on.

File your casting surface flat where the heating transistor goes.

Also have a look at the clearance between the casting and
solder pads of the heater transistor. It is close, sometimes the
casting touches the solder pads. File a small bevel on the bottom
of the casting where the transistor is fitted just for clearance.
You probably wont have this problem with the early ovens
but you will with the later ovens.

Next, have a look at the emitter resistors for the heater transistor,
I bet they are way out of tolerance like you found elsewhere.
Instead of 1.2 or 1.5 ohms, I cant remember exactly, they will have
gone very high in value and the oven will take ages to heat up.
They should have fitted nice little wire wound types in this spot.

Here is the part that everybody falls foul of. After all the screws
are removed from the oven casting, it still does not come off.
A little force is used and then we have a broken thermistor.
The thermistor is cemented into the base of the casting. The
thermistor leads are soldered to the tracks on the PCB. A little
warning label could have fitted to warn technicians to unsolder
thermistor before removing the casting. Words of warning
etched on PCB would have been fine.
A label would have cost money, but heaps of time and money
were spent drilling out the thermistor with the snapped leads.
Having the thermistor not glued in to the casting is fine provided
heaps of that white heatsink compound is used to fill the hole
where the thermistor goes. Cemented in is better but the risk of
damage is great. So Jeff, watch out for the thermistor.

Regards,
John Crighton
Hornsby

 

[Brian Goldsmith]

"John Crighton" wrote :-


while we were discussing the shitty resistors,---- (and lotsa other good
info about the RA7915)

However,I am looking for the upper and lower sideband crystal filters
for a 7915.
Any hope?

Brian Goldsmith.

 

[Jeff]

Thanks for the advice John. I havent looked at the oven oscillator closely
yet, but is the non PLL version, which has provision for 6 channel crystals.
There is the 10.7Mhz carrier insertion crystal as well - but thats all in
the way of crystals. The heater transistor is a 40250. This would be the
early version I presume. Is this model OK John, or did it suffer the same
mechanical defficiencies?
JEFF

 

[John Crighton]

"John Crighton" wrote :-


while we were discussing the shitty resistors,---- (and lotsa other good
info about the RA7915)

However,I am looking for the upper and lower sideband crystal filters
for a 7915.
Any hope?

Brian Goldsmith.

Hello Brian,
I don't have any printed info on the RA7915 but I am guessing
the filters would be the same as used in TRA7928 &TRA7948
transcievers which were re-badged AWA SS90 and SS901.

I have seen these transcievers sell for around $50 at Ham
trash and treasure/field days. Those transceivers only had
filters fitted for upper side band usually, but a lower sideband
filter could be put in its place if the customer desired LSB, so
you may still have hope for a lower sideband filter.

I just had a look at an old TRA9848 and the filter is
TOYO COM EQUIP CO. LTD
Type 10ML8 Freq 10.7 Date 11-72

If Jeff can give us the details from his filter then we will know
for sure if filters from the old transceivers are the same.
I am guessing they are the same but I am not 100 % sure.

I would imagine Hy-Q in Melbourne would have something
similar for sale that would do the job. I know they were about
seventy dollars 25 years ago from Hy-Q. With stuff like this
you can never tell about prices today compared to long ago.
It might be expensive or surprisingly cheap. Send Hy-Q an
e-mail just for interest.

There is Ham trash and treasure auction coming up at
Rose Bay soon here in Sydney, early June I think.

Regards,
John Crighton
Hornsby

 

[Jeff]

Hi John, Brian,
The USB filter in my RA7915 is a Toyo 10MLS. Freq 10.7mHz, Mfg no R052, Date
3-71.
JEFF

 

[Jeff]

Thanks John,
Ive done some more refurbishment. When I tried the board, the mute didnt
work, and it wouldnt select AM mode. Traced to 2 transistors that had both
gone open circuit for no reason. When I desoldered them , the leads fell out
of the transistor body. They were probably nudged during rework, and prone
to internal damage if disturbed. Both were the same type, AY1114. Replaced
with BC557, and all OK. Have you heard of these blob transistors giving
trouble John?
JEFF

 

[John Crighton]

Hi John, Brian,
The USB filter in my RA7915 is a Toyo 10MLS. Freq 10.7mHz, Mfg no R052, Date
3-71.
JEFF

Hi Guys,
I have had another look again at my filter.
Last Friday that S looked like an 8 to me. Under a magnifier it is S
So Brian, the filter in my transciever TRA7948 is
TOYO 10MLS. Freq 10.7MHz. Mfg no U 121. Date 11-72

The Mfg no R052 and U 121 are different. I don't know what
this means but I would be happy to use a filter from a transciever
that can be picked up fairly cheaply.

Regards,
John Crighton
Hornsby

 

[John Crighton]

Thanks John,
Ive done some more refurbishment. When I tried the board, the mute didnt
work, and it wouldnt select AM mode. Traced to 2 transistors that had both
gone open circuit for no reason. When I desoldered them , the leads fell out
of the transistor body. They were probably nudged during rework, and prone
to internal damage if disturbed. Both were the same type, AY1114. Replaced
with BC557, and all OK. Have you heard of these blob transistors giving
trouble John?
JEFF

Yes, I remember that happening to me several times with those
particular blob transistors as you call them, and I wasn't even
being rough. The legs just fell off. Heh heh heh....
Regards,
John Crighton
Hornsby

 

[budgie]

while we were discussing the shitty resistors, I just remembered
the shitty oven oscillator resistors and lousy workmanship
on the oven casting. (snip)

I want to warn you about the "later model" oven oscillator unit.
The heater transistors, are screwed to the side of the oven
casting. Fair enough, but the casting is very rough and uneven,
the lazy bastards in production would not file it flat. So the
contact between the casting surface, mica washer and flat
pack power transistor BD??? is bad. To make matters
worse, the little brass threaded insert that is pushed into the
casting to take the screw of the power transistor sometimes
stands proud of the casting. Meaning there is a gap between
the power transistor and casting when screwed up. The
thin mica washer can get damged by the proud insert and
not insulate the transistor from the casting. Out the door they
went just like that for other people to fix in the field when
they failed later on.

File your casting surface flat where the heating transistor goes.

Also have a look at the clearance between the casting and
solder pads of the heater transistor. It is close, sometimes the
casting touches the solder pads. File a small bevel on the bottom
of the casting where the transistor is fitted just for clearance.
You probably wont have this problem with the early ovens
but you will with the later ovens.

Next, have a look at the emitter resistors for the heater transistor,
I bet they are way out of tolerance like you found elsewhere.
Instead of 1.2 or 1.5 ohms, I cant remember exactly, they will have
gone very high in value and the oven will take ages to heat up.
They should have fitted nice little wire wound types in this spot.

Here is the part that everybody falls foul of. After all the screws
are removed from the oven casting, it still does not come off.
A little force is used and then we have a broken thermistor.
The thermistor is cemented into the base of the casting. The
thermistor leads are soldered to the tracks on the PCB. A little
warning label could have fitted to warn technicians to unsolder
thermistor before removing the casting. Words of warning
etched on PCB would have been fine.
A label would have cost money, but heaps of time and money
were spent drilling out the thermistor with the snapped leads.
Having the thermistor not glued in to the casting is fine provided
heaps of that white heatsink compound is used to fill the hole
where the thermistor goes. Cemented in is better but the risk of
damage is great. So Jeff, watch out for the thermistor.

Does that apply to the TRA7928/38 transceivers as well? It's a long time since
I've looked inside them - although I have a working '38A stowed in the garage.

 

[Jeff]

Hi John,
The Oven unit is next on the list for a look at. I'll be checking all the
resistors, including the one you mention.
I'm going to do the mod to widen the freq range of the clarifier into a BFO,
I see there is a cap that changes value if clarifier or BFO mode is wanted.
Another thing, I might disable the heater, to see if the xtals are stable at
room temp. Ive read this was a common mod that was done to these sets?
JEFF

 

[Brian Goldsmith]

"John Crighton" wrote I have had another look again at my filter.
Last Friday that S looked like an 8 to me. Under a magnifier it is S
So Brian, the filter in my transciever TRA7948 is
TOYO 10MLS. Freq 10.7MHz. Mfg no U 121. Date 11-72

The Mfg no R052 and U 121 are different. I don't know what
this means but I would be happy to use a filter from a transciever
that can be picked up fairly cheaply.

**** John,many thanks for your efforts.A large dollop of luck saw me
pick up a cheap single channel 7915 over the weekend,and,yes,it is
fitted with the USB filter!!!

Regards,Brian Goldsmith.