Intek HR-2800 AM/FM transceiver DC-DC board.

[mastercare]

hi guys anyone ever worked on one these?
i bought it cheap and found th dc>dc converter board has a few shorted components prob reverse connected....my question is...im only going to use on 12v the purpose of the dc.dc board is to allow 12v 24v up to 32v inputs...
so surely i can do away with it?
any comments or anyone perhaps has had one wpuld be great...
cheers
paul
g4sbx

[SiriusHardware]

A nice circuit diagram and layout drawing for the radio here:-

http://www.cbradio.nl/intek/ServiceM...00_ENG_ITA.pdf

The circuit of the 'converter', which looks more like a linear regulator to me, is on page 1 of that manual. It's a good thing that it is a linear circuit actually, I was thinking 'who in their right mind would put a switch-mode power supply inside an HF radio'.

I agree you can probably try running the radio directly on 12V. It might have to be exactly 12V, which the converter is intended to produce, rather than 13.8V - the extra couple of volts may put the radio outside of its comfort zone.

[G6Tanuki]

Originally Posted by SiriusHardware

The circuit of the 'converter', which looks more like a linear regulator to me, is on page 1 of that manual. It's a good thing that it is a linear circuit actually, I was thinking 'who in their right mind would put a switch-mode power supply inside an HF radio'.

RACAL did just that in the RA217 - so it could be used on any-polarity 12-30V AC/DC supplies. Even when running on mains current it used the SMPS. And Pye did the same with their 24V in-truck-adapters for the 290-series two-way radios and the rather-rare adapters used to power said radios off 48VDC telephone-exchange/datacentre supplies.

As to the OP's requ4est, yes unless you're needing to run the radio off 24V then you should be able to bypass the voltage-converter and feed it directly with 13.8VDC of the appropriate polarity.

[SiriusHardware]

I imagine that in the RA217 (which I don't know at all, but was probably 100 times the price of this radio) it would be exceptionally well screened and filtered.

The Pye / Philips 29x series were on VHF and upwards where the hash typically produced by such circuits is not likely to be as intrusive.

In this radio the designer of the regulator has gone to unusual lengths to make the output stable, even including temperature compensation, so that did make me wonder if the input supply voltage is critical for the radio to operate within spec. Two volts more could increase the RF output power by a significant amount.

[CambridgeWorks]

Pye even did it in the late 60s for the W15 Westminster series and in the 70s for the Europa series. Not such a horrible sharp edge waveform as smps of today though.
There was a rare Europa HF lookalike, the SSB170 that also could use the 24-12 OR 12V to 12V isolated converters. I have one! 2- 10MHz iirc.
Rob

[mastercare]

Hi thanks guys for all your input...i will fit the faulty parts ive ordered..and try and keep it org...but if all fails as you say i can take the red wire from the dc>dc board and connect it to the red supply wire coming into rig....guess i could disconnect the output from dc>dc board when new parts fitted see if i get a stable voltage before making final connections....
for those with circuit parts blown
1 protection diode on main board in4003
2 18v zenor diode short
3 Q6a mje3055 short

im hoping there is no other damage...of course the micro could be stuffed...
we will find out...thanks agn...at least i know i can do away with dc>dc board if i have to..
thanks
paul
g4sbx

[SiriusHardware]

A small detail I have just noticed - when the input supply voltage is under a certain voltage the 'voltage check' block turns on the relay RLA1 which then connects the input + terminal of the 'converter' straight to the output + terminal.

So, when running on 12V the regulator does not really come into play at all, although some parts of it are still connected to the input and output terminals so it needs to work / not have any faulty components in it even if it is not being actively used.

[mastercare]

Hi all just a update...parts arrived and fitted...no smoke wound up voltage saw display light up...voltage up to 13.8v and rig stayed on ok...so org dc>dc board restored...no sound till pins shorted due to req mike plugged in...
but overall a success. its now on 10 meters working quite well..pk power about 20 watts...prob the best rig in town if it had ssb...
oh well thanks guys for all your help on this one...
paul
g4sbx

[SiriusHardware]

One further step you might like to try is to disconnect the output of the DC-DC converter from the radio and then wind the input voltage to the converter up to +24V and make sure the output of the converter really is holding, regulated at 12V or 13.8V.

As mentioned above, the converter essentially just swings itself out of the way when the radio is running on 12 or 13.8V so the only sure way to check that the converter is really repaired is to power it from 24V - but disconnected from the radio initially, in case the regulator is NOT working.

Although you've said that you yourself only ever intend to run it on 12V, you (as a radio amateur) may eventually find the lack of SSB on 10m a little bit limiting and decide to sell the set on, in which case it may well be bought by someone who wants to put it in a larger vehicle.