Philips (Simoco) PRP74 help

[Damo666]

I've just picked up some Philips PRP74 radios, however, because I don't have any batteries for these I can't establish which battery terminal on the radio is + or -.

I've downloaded the service manual, and despite the fact I've looked through over 170 pages I can't find the answer.

Can anybody tell me which terminal is which, and also tell me what the remaining one is for, please?

[Biggles]

I think there is a couple of these at work. I can look tomorrow, but you could try a continuity test between any exposed metalwork on the set and each terminal with the set switched on and no battery in. The negative terminal is normally strapped to the metalwork i.e. zero ohms. This is obviously not a 100% certain test.
Alan.

[Damo666]

Hi Alan,

I considered doing that, but there's no exposed metalwork on the radio - not even on the antenna connector as it's just a "live" thread for the stubby.

Things like this are easy to decipher on most similar Motorola gear as there's a proper SMA connector on the head, and the chassis denotes the battery polarities.

[SiriusHardware]

Is this the diagram you downloaded? If not, may prove useful.

http://pmrconversion.info/manuals/pye/PRP73_srv.pdf

On 'PDF page' 62 of 177 of that document there is a diagram of the programming lead (something you may need sooner or later anyway) and if you examine it in detail it shows that stud #2 on the 'facility connector' on the side is 0V. (The diagram has a little picture of the facility connector showing you how the studs are numbered).

I have a VHF pair of these mothballed somewhere but the batteries will be long dead, though I notice there are still plenty of third party batteries available, some at reasonable prices.

[SiriusHardware]

...also, page 54 of 177 shows the diagram for a dummy battery, with two main and two other connections to the battery. Since your radio only has the three contacts it probably lacks the data connector, therefore the third terminal may be for reading a thermistor in the battery pack.

[SiriusHardware]

...And page 39 of 177 has a much better diagram of the facility connector.

[Damo666]

That's the same PDF manual I downloaded, but the page layouts are different - so thanks for the heads up.

I realised that the screws holding the casing together were grounded to the chassis, so with the continuity tester on my DMM I managed to establish that the pin on the far left looking at the rear of the radio was negative.

I then alternated the positive between the middle pin and remaining right pin (perhaps Thermistor control as said), and the radio switched on & functioned fine when connected to the middle.

Do you think I'll have damaged anything by temporarily connecting +7.2v to that far right pin?

Some of the information/schematics shown on the PDF are a little too technical for me, hence the question.

[Biggles]

The radios we have are actually PRP73s, but I think they will have the same pin outs. The battery voltage is 7.2V which you probably already know. The battery connections are as follows. Looking at the rear of the set with the battery removed, there are actually four positions but on ours the far left is unpopulated. So to start from the far right, it is marked "A" whatever that means. Next one in from the right is B+, next one in from right is B-. Just to avoid any confusion. Starting from the left, blank, B-, B+, "A". A may be a programming connection, although the battery actually has connection studs for all four connections, even the empty one on the radio. Hope that helps.
Alan.

[SiriusHardware]

Originally Posted by Damo666

Do you think I'll have damaged anything by temporarily connecting +7.2v to that far right pin?

I haven't gone into the diagrams again yet but the straightforward answer to your question is that either you have already damaged something or you haven't - the event has already happened or not happened, so you may as well just proceed in the hope that you didn't damage anything.

If the input is meant for sensing a thermistor then hopefully there is a network of resistors between that terminal on the radio and whatever actually does the sensing.

Compared to the earlier Pye / Philips diagrams / manuals, I have to say that service manual looks pretty horrible, not like their earlier style at all.

I know you haven't got there yet, but when you get to programming the radios the advice I was given by a Pye / Philips / Simoco engineer (and fellow radio amateur) was to always read the configuration from a working radio, save it as a file, modify only what needs to be modified (channel frequencies, etc) and send the modified configuration back. This (he said) also applies to the Philips PRM80 mobile series of radios, which were contemporaries of the PRP handheld series.

Apparently the configuration includes a lot of stuff which is quite chassis / model specific and if you try to program one from scratch you could set obscure parameters which don't apply to your version and get into quite a muddle.

[Damo666]

Thanks for helping me along.

The radios work fine & talk back to back, but until I source some batteries & a charger, I won't know if I've done any damage to the sensing terminal - if that's what it is.

Those diagrams provided in the service manual are far too complicated for me so I can't work out exactly what that pin denotes, and as you rightly say - this service manual isn't on par with many other manuals for this type of gear.