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Old 11-12-2017, 1:38 AM
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Default ICOM ICR-7000 receiver power transformer replacement

About 28 years ago I bought new an ICOM R-7000 receiver. A few years later when I upgraded my shack, I sold it to a freind of mine who has used it daily all these years.

Suddenly it is blowing the primary 1 amp fuse and with the bridge rectifier disconnected it still blows.

So with some certainty it appears the power transformer has failed.

Can anyone suggest :

1) a source for an OEM transformer ? Used or NOS?

2) the parameters of this transformer such as turns ratio, secondary voltage, VA etc so we can locate a suitable replacement.

The original appears to be a Core type arrangement and has multiple primary taps for regional voltage changes.

I am thinking a toroidial transformer might work, but am hesitant to recommend a selection without the electrical specs.

The service manual is not helpful beyond the part number.

I was going to suggest a new ICOM receiver, but this radio is repair worthy.

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Old 11-12-2017, 12:15 PM
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Send an email to Scott Malcolm tomorrow and he might know of a source for a replacement.

Malcom Technical Support

He has repaired several radios for me and is well known as a reliable tech in Ham Radio servicing especially ICOM and Kenwood equipment.

Last edited by SouthOrRadio; 11-12-2017 at 12:18 PM.. Reason: spelling
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Old 11-12-2017, 12:50 PM
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Thanks! I have sent him a note.

From time to time I see these radios broken up and sold as parts on ebay. but none currently.
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Old 11-12-2017, 1:53 PM
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Run it on a good linear external 13.8volt power supply. You could even remove all the power supply components. Gets rid of all those heat-generating bits.
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Old 11-12-2017, 2:04 PM
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Run it on a good linear external 13.8volt power supply. You could even remove all the power supply components. Gets rid of all those heat-generating bits.
Yeah, I have an R-9000. It has a similar, but higher amp power supply. I have a fan fitted to the rear heatsink which helps a lot. I think it has same but larger, Core type transformer. Those apparently are less efficient. I will have to monitor the temp of that transformer. Mine has low operating hours and I re-capped the PS years ago proactively. My only failure was the VFO shaft encoder after a period I was using it a lot.

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Old 11-12-2017, 2:57 PM
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Quote:
Originally Posted by majoco View Post
Run it on a good linear external 13.8volt power supply. You could even remove all the power supply components. Gets rid of all those heat-generating bits.
Good advice! That was being recommended when they were first introduced by Icom new! They run very hot with Icom's internal power supply. You could almost cook a TV dinner on top of them!

I used to own both an IC-R7000, and the IC-R71. Both acquired a lot of problems as they aged.
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Old 11-13-2017, 2:09 PM
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Alright, now that you have some other opinions, I just measured the current draw of my ancient R7000 from my homebrewed 13.8v well regulated power supply and it takes about 1.2Amps on the front panel meter. This means that you don't have to spend a fortune buying a huge PS to run it - unless of course you want to do what a lot of us do and that is run every nominally 12v device from the one power supply. So survey all the power supplies you can and deduce what is best for you. The only thing you have to check is that you can find the plug to fit the strange Icom socket - initially I made one by filing down an old hard drive connector and refitting the Molex pins into the required positions.
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Old 11-13-2017, 2:17 PM
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Originally Posted by majoco View Post
Alright, now that you have some other opinions, I just measured the current draw of my ancient R7000 from my homebrewed 13.8v well regulated power supply and it takes about 1.2Amps on the front panel meter. This means that you don't have to spend a fortune buying a huge PS to run it - unless of course you want to do what a lot of us do and that is run every nominally 12v device from the one power supply. So survey all the power supplies you can and deduce what is best for you. The only thing you have to check is that you can find the plug to fit the strange Icom socket - initially I made one by filing down an old hard drive connector and refitting the Molex pins into the required positions.
Thanks for the information on the current draw. If this weren't a receiver I would suggest installing a small switcher PS inside of it. My freind wants to fix the AC supply, it provides portability if you take it somewhere on a whim.

Now looking at ways to restore the unit and reduce the heat. These have a Core type transformer in them. I thought it was a toroidial but it isn't. I have no idea why they chose that type of transformer. The R9000 has same type. From what I read they are less efficient and that equals more heat. A toroidial might be a better choice if the inrush current isn't a problem
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Old 11-13-2017, 4:11 PM
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If a transformer is less efficient, the magnetism is saturated and convert much of the energi to heat, it also will swallows spikes from the power line very efficient. It is a way to protect the semiconductors in the power supply but the heat will also dry out the capacitors and age them prematurely.

/Ubbe
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Old 11-13-2017, 5:06 PM
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I haven't done any investigation around the power supply but it does seem a rather over-complicated circuit for just a couple of amps. Somebody said that a lot of heat comes from the bridge rectifier but I did notice that the series pass transistor has a very poor heatsink arrangement - both mounted close together on the back panel. I'm not overly sure about the function of that 56ohms across the regulator either - perhaps it may reduce the dissipation of the series pass transistor but the heat developed in total will be the same. In theory according to the schematic there should only be about 4watts generated from the regulator but it feels a darn sight more than that.
Just to be stupid (!) has any of you guys in the US tried setting the transformer taps for 200volts then trimming the voltage set potentiometer for 13.8v volts or an near as you can? It might not be physically possible with the voltage selector plugs - I'll investigate....
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Old 11-13-2017, 5:36 PM
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Quote:
Originally Posted by majoco View Post
I haven't done any investigation around the power supply but it does seem a rather over-complicated circuit for just a couple of amps. Somebody said that a lot of heat comes from the bridge rectifier but I did notice that the series pass transistor has a very poor heatsink arrangement - both mounted close together on the back panel. I'm not overly sure about the function of that 56ohms across the regulator either - perhaps it may reduce the dissipation of the series pass transistor but the heat developed in total will be the same. In theory according to the schematic there should only be about 4watts generated from the regulator but it feels a darn sight more than that.
Just to be stupid (!) has any of you guys in the US tried setting the transformer taps for 200volts then trimming the voltage set potentiometer for 13.8v volts or an near as you can? It might not be physically possible with the voltage selector plugs - I'll investigate....
A simple, no mod voltage reduction could consist of an outlet box with a cord, inside a center tapped filament transformer with its secondary tapped to buck 3 or 6 volts from the line voltage. Being that most US service is close to 120V and not the designed 117 VAC, you could feed the radio its nominal 117V or even 114 V and reduce the power and heat somewhat.

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Old 11-13-2017, 10:26 PM
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I believe a toroidal transformer will be larger than a more conventional laminated core transformer of the same wattage rating and the toroidal will have worse voltage regulation. The only real benefit a toroidal has is low EMI.

What I would do in the same situation is power the receiver from a variable power supply connected to the bridge rectifier in the 7000 and find what input voltage to the regulator is needed for it to finally regulate at its rated output voltage. Then calculate what AC secondary voltage would be needed with the stock capacitor input power supply to provide maybe 2 or 3 volts more than that.

The end result should be a much cooler running power supply as I suspect the original had far too high of an input voltage to the regulator creating lots of extra heat in the pass transistor. It should be easy to find a suitable transformer on Epay that fits the space, has slightly higher wattage rating and maybe the same mounting arrangement.

It would be nice if someone with a working R-7000 could measure the voltage at the large filter cap in the power supply and also measure the regulated voltage powering the radio as a baseline for a repair like this.
prcguy



Quote:
Originally Posted by RFI-EMI-GUY View Post
Thanks for the information on the current draw. If this weren't a receiver I would suggest installing a small switcher PS inside of it. My freind wants to fix the AC supply, it provides portability if you take it somewhere on a whim.

Now looking at ways to restore the unit and reduce the heat. These have a Core type transformer in them. I thought it was a toroidial but it isn't. I have no idea why they chose that type of transformer. The R9000 has same type. From what I read they are less efficient and that equals more heat. A toroidial might be a better choice if the inrush current isn't a problem
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Old 11-14-2017, 12:19 AM
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Quote:
Originally Posted by prcguy View Post
I believe a toroidal transformer will be larger than a more conventional laminated core transformer of the same wattage rating and the toroidal will have worse voltage regulation. The only real benefit a toroidal has is low EMI.

What I would do in the same situation is power the receiver from a variable power supply connected to the bridge rectifier in the 7000 and find what input voltage to the regulator is needed for it to finally regulate at its rated output voltage. Then calculate what AC secondary voltage would be needed with the stock capacitor input power supply to provide maybe 2 or 3 volts more than that.

The end result should be a much cooler running power supply as I suspect the original had far too high of an input voltage to the regulator creating lots of extra heat in the pass transistor. It should be easy to find a suitable transformer on Epay that fits the space, has slightly higher wattage rating and maybe the same mounting arrangement.

It would be nice if someone with a working R-7000 could measure the voltage at the large filter cap in the power supply and also measure the regulated voltage powering the radio as a baseline for a repair like this.
prcguy
Those are good suggestions. Especially the variable voltage experiment.

The existing transformer is an odd "core type" that at first glance looks like a toroid, but is not, it is an oval core (picture Indy 500 race track) with split primaries and secondaries wound around the long portions. It is not an EI type lamination like the R71 receiver has. I am at a loss why they chose that style, what performance advantage it would have. My R9000 has same type, but much larger.

The R7000 schematic says 15V at the secondary which I assume is RMS and about 17.X volts DC at the first filter cap.

Manuals for the R71 and R9000 peg the transformer at 14.5 and 16.5 V respectively for a similar topology.

My friend is still troubleshooting. I have him double checking the 117V wiring, the bypass caps and switch to make sure no fault on the primary side. He has measured 350 milli ohms on the secondary. But I am not sure that reflects a short. All we know at this point is that switching it on blows a fuse. There has been no smoke, no smell, no sparks, no toasty parts. I am hoping it's the switch, but those are rare as well.

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Old 11-14-2017, 8:11 AM
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It sounds like its a toroidal type and with a layered sheet metal toroid core it would have good primary to secondary isolation for RF-EMI rejection, etc. If it were mine I would not hesitate to replace the transformer and regulator with a low voltage drop 3 terminal regulator IC.
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Originally Posted by RFI-EMI-GUY View Post
Those are good suggestions. Especially the variable voltage experiment.

The existing transformer is an odd "core type" that at first glance looks like a toroid, but is not, it is an oval core (picture Indy 500 race track) with split primaries and secondaries wound around the long portions. It is not an EI type lamination like the R71 receiver has. I am at a loss why they chose that style, what performance advantage it would have. My R9000 has same type, but much larger.

The R7000 schematic says 15V at the secondary which I assume is RMS and about 17.X volts DC at the first filter cap.

Manuals for the R71 and R9000 peg the transformer at 14.5 and 16.5 V respectively for a similar topology.

My friend is still troubleshooting. I have him double checking the 117V wiring, the bypass caps and switch to make sure no fault on the primary side. He has measured 350 milli ohms on the secondary. But I am not sure that reflects a short. All we know at this point is that switching it on blows a fuse. There has been no smoke, no smell, no sparks, no toasty parts. I am hoping it's the switch, but those are rare as well.

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Old 11-14-2017, 9:04 AM
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Quote:
Originally Posted by prcguy View Post
It sounds like its a toroidal type and with a layered sheet metal toroid core it would have good primary to secondary isolation for RF-EMI rejection, etc. If it were mine I would not hesitate to replace the transformer and regulator with a low voltage drop 3 terminal regulator IC.
prcguy
Would you replace the transformer with a ferrite toroidial?

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Old 11-14-2017, 9:39 AM
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I don't see a reason why unless there are very low level audio stages nearby that would be subject to induced hum from transformer fields.
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Would you replace the transformer with a ferrite toroidial?

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Old 11-14-2017, 11:58 AM
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Quote:
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I don't see a reason why unless there are very low level audio stages nearby that would be subject to induced hum from transformer fields.
prcguy

The proximity to low level stages is a good question. There is a lot going on in that chassis. Which is why I wonder why they use that oval Core style transformer rather than a traditional E I laminated core.
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Old 11-14-2017, 3:51 PM
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Quote:
Originally Posted by RFI-EMI-GUY View Post
The proximity to low level stages is a good question. There is a lot going on in that chassis. Which is why I wonder why they use that oval Core style transformer rather than a traditional E I laminated core.
Probably due to much less magnetic field from the transformer. We used that type of transformer in test equipment.

I would set the receiver up for external 12 volt input. And use a remote power supply. All tho I have not seen the ICOM ICR-7000 receiver schematic.
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