Royce 651 schematics needed

[wiselynx]

hi everybody,

I recently acquired a Royce 1-651 CB radio. I purchased it at a very cheap price, and I was not totally surprised to discover that while it receives fine, it's not able to transmit. After some basic tests on the final stage, I would need the radio schematics for further troubleshooting.

I was disappointed discovering that very few information is available on the web. I found some sources pointing to old SAMS issues, that are reported to hold the information I'm looking for; alas, they would charge me more than 20$, which is already more than five times what I paid for the radio. Being not sure if I'll be able to repair it or not, I'd really rather avoid such an expense...

I'm writing you for advice on where I could find such schematics; any suggestion will be welcome!

 

[loosecannon]

im guessing that the radio you are wanting info for is the royce 651 and not 1-651.

you're probably not going to find a schematic of this obscure radio online, but here is a SAMS for it for 10 bucks total.

SAMS PHOTOFACT CB #277 Johnson Messenger 80 PRESIDENT - eBay (item 140500688438 end time Feb-12-11 18:19:17 PST)

good luck,
LC

 

[wiselynx]

im guessing that the radio you are wanting info for is the royce 651 and not 1-651.

mh, you're confusing me. from what you say I assume 651 and 1-651 are not the same.. I don't have the radio at hand to check now, so I don't remember what's written on the back; on the front I'm sure the writing says "Royce CB651".

you're probably not going to find a schematic of this obscure radio online, but here is a SAMS for it for 10 bucks total.

thaks for the hint; alas it's again more than 20$ to have it shipped to Italy, and again, I'd rather not spend such amount being not even sure I'll be able to fix the radio. My hope is to find someone that has the schematics and is willing to share it with me for free..

 

[loosecannon]

well i hope you find someone willing to do that, but i wouldnt get my hopes up.

maybe there is a chance we can fix it without the schematic.

what tests have you done so far?

exactly what is happening/not happening in the transmitter?

do you show any power out? in any mode? (not sure if this is an AM only radio or not)

it is possible to remove the driver and final transistors and test them with a digital voltmeter to determine if they are open or shorted.

just google "testing semiconductors with a DMM" for the procedure.

the more details you can give, the more chance there is of getting help.
LC

 

[wiselynx]

uhu.. if we manage to fix it without the schematics, it'd be perfect

ok, I'll try to better explain. The radio is AM only AFAIK. It has a switch to commute from low to high transmission power, and a small internal power meter.

If it's set on low power, it simply won't transmit; trying to do so will increase the absorbed current by around 100 or 200 mA, I can hear a "click" sound from the circuit board (could it be a relais?), but no sound is transmitted to a nearby test radio. The internal power meter moves very slightly.

If set on high power, it will instantly draw 3A from the power supply, even without actually trying to transmit. The power meter jumps to over half the scale, and its backlight fades.

I noticed a very strange wiring on the lo/hi power switch (compared to the wiring of the other 3 similar switches), and I suspect some one previous owner messed something up. In particular, there are two big (could be 2-4 W) resistors in parallel one each other, and I noticed that by only powering the radio on they will get soon very hot, even without transmitting and even with the hi/lo power switch in low position. Trying to transmit will instantly turn them so hot that you can't touch them. If needed I can both post pictures and a small schematics of that part of the circuit (it's quite simple) but I have no idea where the wires go in the main circuit board..

About the final stage transistor, I already tested the original one, and in doubt I acquired a new one (yes, it was cheap enough..), and they both seem to read fine.. I cant say the same about the drivers, as there are many other transistors on board and without schematics I find it hard to locate them.

thank you very much for the hints

 

[wiselynx]

one more element: I noticed that, with the lo/hi power switch in the "low" position, I can get Larsen effect if trying to transmit with the microphone near the test radio speaker. This leads me to think there is some strange, wrong wiring that draws most of the power to the aformentioned resistors withe the "low" settings, and produces a short circuit when in "high".

 

[wiselynx]

further evolutions.. I managed to transmit, but there are still many questions.

First, I unsoldered all wires and resistors, so that I could understand exactly the switch functioning. The switch has 12 pins, and acts as three separate switches, with the following connections:

switch off:
1-2, 4-5, 8-9, 11-12
switch on:
2-3, 5-6, 7-8, 10-11

From that, I could draw the schematics of this small part of the circuit. I had two yellow wires (which I'll call A and B), a black wire, the two resistors (27Ohm each, originally in parallel) and one of the leads of a diode (being the other lead somewhere else). Connections to the switch were as follows:

1 to yellow wire A
2 to yellow wire B
5 and 8 to the diode
6 and 7 to black wire and one end of resistors
12, 11, 10 and 9 all connected together and with the other end of resistors

Simplifiyng things, that meant:
- with switch open, I had the black wire connected to the diode through the resistors, and yellow wires A and B connected together
- with switch closed, I had the black wire directly connected to the diode, and yellow wires disconnected

Next, I measured voltage of the different affering wires and components relative to ground. The diode measured around 13V. yellow wire A was around 9V, yellow wire B and black wire were around (but not exactly) 0V.

Said that.. I did some experiments, and I found out that:
- with just one of the resistors (instead of the parallel of two) connected between the black wire and diode permits transmitting with a drawn power of around 1A
- connecting or not the two yellow wires together doesn't seem to make any difference
- the internal meter seems not to be showing the output power, as it doesn't move while transmitting
- connecting the yellow A wire to the diode or black wire wile transmitting causes the audio to interrupt for a few seconds, wile connecting the B wire doesn't do anything
- connecting the black wire directly to the diode achieves the exact behaviour I was having at first: the backlight dims, the power drain jumps to fixed 3A
- whatever I do, if resistors are connected they rapidly get very hot

Said that, I'm already quite happy I managed to make the radio transmit.. I think I coukld arrange resistors and switch so that in low power config both resistors are in series while in high power only one is connected; I still wonder anyway what's the meaning of the yellow wires, and if it's normal for the resistors to get that hot..

 

[wiselynx]

ok, seems like I solved without schematics. I'm not sure what I did is right, but it seems to work, and I'm quite satisfied..

I simply rearranged the components before mentioned so that when the hi/lo power switch is "low", only one resistor is used, while when "high" both are used in parallel, resulting in higher current and (I suppose) higher RF output power.

thanks loosecannon for helping; should anyody ever find those schematics, I'd be still curious to see what was supposed to be the original circuit