Icom IC-910 circuit help

[VK4UH]

Thanks for reading this

My trusty Icom IC910 has developed a Tx fault on 2 and 70 with no output on either band. (23 cms from the separate module is working normally)
Rx is normal on all bands. The rig is switching on PTT OK and draws the appropriate amount of standing current to the spearate PAs on both 2 and 70.
Low level Tx signals are audible and normal on an external receiver on both 2 and 70.
Since the 910 has separate drivers and PAs for 2 and 70 it appears there is a fault on some common part of the drive chain before the driver stages but after the point where 23 cms drive is taken off - at least to be explained from a single fault.

My immediate problem is I have misplaced the circuit diagrams for the 910! - The dog ate my homework.

Are there any other '910 owners locally in SE VK4 who might loan me the circuit diagrams until I find mine?

Also interested to hear from anyone who has seen a similar problem

Regards
Kevin VK4UH Brisbane
drkevinjohnston@bigpond.com

[VK2XAX]

While I dont know what your fault might be, you can download the Service Manual here.....

http://www.download.n7tgb.net/Icom_Manu ... manual.pdf

cheers

Tim

[VK4CZ]

Have Service Manual and CCTs... I can drop them in, or just drop by.

[ZL1RS]

Hi Kevin,

Deja vue

The pre-driver FET is common to both VHF and UHF paths and was a bit troublesome. It is the same device as used in the (early model?) FT-817 finals which were apparently notorious for dying ... google FT-817 blown finals club for the info. There is a more robust replacement (Mitsubishi RD07MVS1) which I fitted to my 910H and could then get good power from the two PA strips when a signal was injected before the common pre-driver stage ... but there was still something else wrong which I have not been back inside to find yet.

Thanks for mentioning the 1296 module will function despite the VHF/UHF TX problem, I have the module to be fitted and your comment might be the catalyst to get that fitted and QRV on 23cm.

73

[VK5PJ]

good old VKLOGGER forums to the rescue, I find myself in a similar situation, my 910 has been a problem child on 70cm transmit for a very long time but I have avoided using it for anything but WSPR power levels.

The power out on FM (and SSB) varies from a 'normal' 60 watts to then fall back to 20 watts then back up to 60 then stay there for a little while but always ends up back at its FAULT condition of around 20 watts. If I wind the power control back to give me around 10 watts it is pretty stable.

A daunting fault for a rig where removing the P.A board is such a complex process. Have done the usual dry joint search around the 70 cm P.A but just when I thought it was okay, the fault returns. Seemingly located it to some where around the pre-driver section as when I flex the PCB the fault an be made to come or go BUT I have not noticed this fault when using 144 MHz.

KJ (VK4UH), did you end up finding a solution for your 910?

ZL1RS (Bob), how did you get the pre-driver board out as I have give mine a red hot go but short of more force it has me foxed

Regards,
Peter.

[VK5PJ]

okay, a quick update, hmm 144 and 432 share the same fault, not sure why I have not noticed it on 144 before, probably as I use the IC-275 for most of my SSB work.

So its either the pre-driver board, soldering of the riser pins on the main PCB or component(s) under the pre-driver area of the main P.A board and not going to be taking that out any time soon.

when I put pressure on that area of the main P.A board the fault can be cleared or induced.

[VK3AXH]

Hi All,

I have also had the same problem on both 2m and 70cm. Colin VK5DK also has had this problem and changed the driver chip and as far as I know it's now
going ok again, I have purchased the chip via Icom but not yet installed it. I have however applied considerable heat to the driver pcb and so far it's continuing to
work ok. With care you can unsolder the small pcb with the 4 vertical pins of both input and output. As there are only a few components on this pcb you could take
them off first and either change the chip or as above apply some extra heat without damaging surrounding bits etc.

Peter VK5PJ as mentioned has a problem on UHF only which I suspect may not be the driver chip as it's common to both bands. I've also had several failures in commercial transceiver PA stages using this type of component ie leadless so not sure if it's a trend or just the component itself.

Good luck and if I can help in any way please let me know.....a surface mount desoldering station is certainly worth it in these situations.

Ian - VK3AXH

[VK5PJ]

Thanks Ian,
it is always nice to know it is not just my 910 that has a similar problem.

Hi All,
I have also had the same problem on both 2m and 70cm. Colin VK5DK also has had this problem and changed the driver chip and as far as I know it's now going ok again, I have purchased the chip via Icom but not yet installed it. I have however applied considerable heat to the driver pcb and so far it's continuing to work ok.
Ian - VK3AXH

mine might be in the early stages of going totally faulty or may indeed just need lots of heat to convince it to surrender to the greater good and just keep working. As the 910 is discontinued and the 9100 a rather expensive step up for just 2 and 70cm (for my use) I want the 910 to keep going a while yet, not yet convinced the FT-991 is the answer ether or the IC-7100.... Oh to dream.

Regards,
Peter

[ZL3RC]

Bit off the main topic but just thought Id put in a comment about the FT-991 being as Peter mentioned it.
Ive had one for a while now and I would have to say I wasn't that impressed at the start but since Ive used it for a while now mainly on 6m and 2m I really like it.
It makes the FT-847 that it replaced look a bit sad.

Dont dismiss it to quickly, dam good radio at a dam good price. No this isn't an add for YAESU Just my 2c worth.

Roger.

[VK4CZ]

Watching with interest... my IC-910H has a 70cm only issue, with very low TX output and the the RX deaf. 144MHz and 1296MHz remain good.

[VK5PJ]

Hi Roger,
a few locals have FT991's and have nothing but praise for them and they seem to be very stable frequency wise.

Bit off the main topic but just thought Id put in a comment about the FT-991 being as Peter mentioned it.
Ive had one for a while now and I would have to say I wasn't that impressed at the start but since Ive used it for a while now mainly on 6m and 2m I really like it.
It makes the FT-847 that it replaced look a bit sad.
Dont dismiss it to quickly, dam good radio at a dam good price. No this isn't an add for YAESU Just my 2c worth.
Roger.

I was a bit put off by the early firmware releases that reportedly made the finals expire.

Keeping an open mind on options but really want the 910 to soar again as I have always been an Icom boy, no idea why, they just click with me in the way they operate.

Peter.

[VK4UH]

Hi all

Its been a few years since I started this forum thread

My problem with 910 (low output on 2 and 70 with 23 preserved)was fixed eventually

Fault was dead pre driver FET which is common to both bands. Also replaced a faulty cap in that stage.

Set has been relegated to portable and standby use these days since being usurped by the 9100

KJ

[VK5PJ]

Update: have been working on how to get the pre-driver FET off its sub board, even bought a cheap hot air gun to try and de-solder it.

Tried the hot air gun on some old PSU boards I have here and that works well on those SMD devices but the heat sinking of pre-driver FET is sucking all the heat away from my efforts to de solder it.

Have tried to lift the board from the main board previously but was no able to get it to shift, maybe the heat sink compound is acting like a glue between the two surfaces and a bit scared to put to much weight behind the lever.

Peter.

Update 2: using the hot air gun I was able to remove the sub board that had eluded my previous efforts to de-solder... I am now a convert, hot air is great for de-soldering multi pin connections. (photos later)

[VK3DXE]

.............. (photos later)

Yes please

[VK5PJ]

To say that hot air soldering is great and every one should give it a go is a bit over the top BUT for certain jobs it makes life so much easier, here is my IC-910 pre driver board that I removed last night. Please excuse the state of it, this was caused by my earlier attempts to remove it with a normal soldering iron and solder wick

pre-driver board removed from 910

Above: There is a heat sink that the FET is soldered too (yes that square blob marked K2975 is a three terminal device) and that in turn is screwed down to the main chassis of the 910.

910 P.A board where the pre driver sits

Above: Here is the spot in the 910 where the pre driver board came from, it sits up on two headers, one for input and one for output

board and heatsink

With the aid of the el cheapo $70 hot air gun from ebay I was able to get the board off in just under a minute (after the gun warmed up) then removing the FET was my next task. - Search for this on ebay to see what I bought : "HUAKO 858D Hot Air Heat Gun" it arrived in just three days.

reverse of board

[VK5PJ]

Here is the pre driver board and the FET (bottom side of the FET that shows the three PADS)

FET and board

Oh here is my Flash filter, yes it is an old style cheapo DVD case, can not remember where we bought them from, it was the only thing I could find in the house that was suitable to diffuse the blast of the flash on my camera (older style SLR). In reality I should buy a proper removable flash but for those who want to try it out at home on a compact camera, it is really worth the effort to soften the light from the flash when taking photos of electronics.

flash filter

[VK4APN]

Peter
have sent email direct.
Paul vk4apn

[VK3ZAZ]

I now have same issue
can someone please tell me the part number and circuit number so I can order from ICOM thanks

ZAZ

[VK4GHZ]

Steve, funnily enough no one has specifically mentioned the designator of the part in question... but if it's the FET on the DRV board, it's Q930, a 2SK2975 FET.

Click on the attachments for full-size.

Australian source FWIW: http://semico.com.au/index.php?option=c ... ber+Search

Pedro has done a great job with the images above.


What I find most interesting is how a topic, now over 6 years old, is still helping other hams.
Try doing that with Stupidbook.

Perhaps the ease of posting on Stupidbook is why many prefer it... but with Facebookers it's all about quick (lazy) instant gratification.

Some people 'get it'.
Most never will.

[VK3ZAZ]

Thanks Adam,
A good logger is the old logger
now to put on my 2x glasses