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Author Topic: Collins KWM-380-- repair / advice / tips?.  (Read 13819 times)
ZS5WC
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« on: September 06, 2013, 07:43:18 AM »

 Smiley Hi All,

I have become the proud owner of the SECOND Kwm-380 in South Africa-(perhaps the whole of Africa as well..), and am about the start the repair process.
YES, I am aware of the CCA, but am asking the question here--so here goes:
The rig has been stored most of it's life, and when the previous owner tried to switch it on-apparently the tantalum caps that supply the synth. board got fried.
It is a bit of a concern--cap's don't just blow willy nilly, but could have happened due to the long storage.
I HOPE one of the regulator pass devices aren't short..

What other things should I look for-perhaps you have restored one of these yourself?.

73 de William
ZS5WC / ZS4L
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W9GB
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Posts: 2616




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« Reply #1 on: September 06, 2013, 08:10:47 AM »

Quote
It is a bit of a concern--cap's don't just blow willy nilly, but could have happened due to the long storage.
Tantalum capacitors, of this era, DID have a habit of launching like a rocket from a PC board.
Dangerous, without safety glasses, when this happens on electronics work bench !
Quote
I HOPE one of the regulator pass devices aren't short..
That can be a potential cause.  Do you know how to test?

There are a handful of top KWM-380 experts in Cedar Rapids, IA area (Collins HQ, radio was mfg. nearby in Anamosa, IA).
These qualified Collins employees (some in support and design) SHOULD be sought for advice -- this radio is NOT for Novice techs, due to scarcity of some parts and  low number of these radios and military HF-380 produced.
Jim Maccani, WØHUP is a very good Collins tech on the KWM-380.

Jim Maccani - WØHUP
4140 Elkhorn Drive N.E.
Cedar Rapids, IA 52411
USA
jimscs@mchsi.com
Phone: +1-319-393-0094

Hal Guretzky - K6DPZ
Land-Air Communications
95-15 108 Street
Richmond Hill, NY 11419
USA
Phone: +1-718-847-3090
FAX: +1-718-849-8279
landaircom@aol.com
« Last Edit: September 06, 2013, 08:19:55 AM by W9GB » Logged
KG6YV
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Posts: 508




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« Reply #2 on: September 06, 2013, 01:38:07 PM »

Oh yeah, I second the opinion/observation that tantalum caps are known for "uncaused" explosion.
I have a Tektronix scope in which a tantalum in the power supply went "boom" luckily while in operation with the covers on.... Tantalum capacitors are bombs when they fail, and they are so
tiny for their explosive power....
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W9GB
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Posts: 2616




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« Reply #3 on: September 06, 2013, 02:07:55 PM »

William -

As I remember, only 2,000 of these radios were produced from 1979-1983.
I lived in that area, when the production lines were ending in 1983.

There were ~ 20 factory modifications for the KWM-380/HF-380 during this period.
http://www.wb4hfn.com/COLLINS/Documents/Brochures/KWM380/Brochure-KWM380.htm

WARNING - The October 1979 Owners Manual - INCLUDING the PDF that is floating around on the web has a MAJOR MISPRINT.  The REAR Power connector wiring shown in 1979 manual is wrong and WILL cause damage to your transceiver.
The correct owners manual is the SECOND EDITION - dated January 1, 1981
and a scanned PDF is available (January 1 , 1981 - Owners Manual), here:
http://www.w2xc.com/pdf/Collins%20KWM-380%20owner's%20manual%202nd%20edition%201%20January%201981%20(sm).pdf

Bob Grinnell at Surplus Sales of Nebraska (USA) acquired many of the remaining/spares parts,
when the KWM-380/HF-380 production lines were shut down in late 1980s.
http://www.surplussales.com/Collins/Collins.html

W2XC personal notes on the KWM-380
http://www.w2xc.com/KWM-380_Notes.htm

In May 1980, Rockwell/Collins produced a training document (PDF, 225 pages):
You will require the KWM-380 Owner's and Service Manuals to go along with this training course.

Self Study Training Course on the Collins KWM-380 Transceiver
http://collinsradio.org/archives/manuals/KWM380_Self_Study_.pdf
« Last Edit: September 06, 2013, 02:26:13 PM by W9GB » Logged
ZS5WC
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« Reply #4 on: September 09, 2013, 12:40:01 AM »

 ;)How about that-two respondents with the same name-!.
Thanks Gregory and Greg for your postings-lots of useful data there and I am sure if I get stuck , I could get help in a flash!.
I am very exited to get the old Gal back on the air-luckily I am very technical , and LOGIC circuitry was my major at college, so it is all a matter of finding the root cause and replacing components that might fail in future-like tantalums in the power supply decoupling circuitry.

Much like the TS-850s with its' capacitor fail issues.

Will send feedback when I get her working.. Smiley

73 de William
ZS4L
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ZS5WC
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« Reply #5 on: April 28, 2014, 01:08:14 PM »

 ;DGot the 380 on the bench yesterday, and had a maiden transmission with her today-replaced a faulty dual op-amp in the 2nd PLL loop.
She works well--BUT, the output power seems inversely proportional to the frequency, i.e. 80m is fine at 90w PEP, 40m is lower at 30w, 20m even lower at 20w, etc..
The LPF filter board maybe?..
Any Rockwell Collins experts out there?

73 de William
ZS4L
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W9GB
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Posts: 2616




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« Reply #6 on: April 29, 2014, 07:26:51 AM »

Re-read the September 2013 answers --
who knows this radio better than the engineers that designed and supported?
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ZS5WC
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« Reply #7 on: April 30, 2014, 12:18:40 AM »

 ;)Thanks , I will follow your advice and links as well!.. I am in the process of signing up with the CCA reflector too.
It seems the LPF relays are switching properly, but output power still seems low on 40m and above.
What I did not check was to see if maybe the WRONG relays are being switched.
Perhaps one bit missing to the latch circuitry.
The PA is drawing roughly the same current on most bands-I deduced this by checking the unregulated DC volt drop when key down-so it is trying to produce power.
Obviously I did this for VERY short times as I don't want to damage the PA IF there are issues.

Cheers,
William
ZS4L
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ZS5WC
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« Reply #8 on: May 04, 2014, 11:37:23 AM »

 :)Long story short:
I found one PT9785 open,(non original) and some damaged bias components.
I removed the PA from the heatsink and overhauled the unit.
I re-in stalled MRF454's , and reset bias. I also included Homebrew gain feedback networks to flatten gain accross the HF spectrum, and improve stability.
Works like a dream--BUT I have discovered the next problem.
On 20 and 10m the rig THINKS it is in the Ham bands, but is actually on a way off frequency.
It transmits, BUT swr is infinite into the yagi, which means the TX and RX frequency is incorrect.
For example 14.000 to 14.300 (on the dial) is FULL of arabic AM stations!. Clearly not correct.
I will determine HOW FAR wrong it is-but this is a very strange problem!.
Any ideas?.

The TX/ RX muting is also not ideal-big POP! in the LS when pressing the PTT.

73 de William
ZS4L
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ZS5WC
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« Reply #9 on: May 05, 2014, 11:24:59 PM »

 ???Wow!, I am amazed-nearly 8100 reads and not a single further reply?..
Where are the experts?.
Did more testing last night, on 14.200 the rig is actually on 15.200 Mhz, on 28.500 the rig is actually on 29.500 mHz.
Seems the LSB bit from the control unit to the PLL is permanently set.
Sooo-will have to trace some bits..

Repaired the coupler board-now getting proper alc action--in fact a bit too much..

73 de William
ZS4L
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ZS5WC
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« Reply #10 on: June 08, 2014, 11:59:17 PM »

 Grin

After fixing the PSU circuitry, repairing the PA, and replacing blown caps, I discovered that the KWM-380 would be off frequency by 1Mhz on some bands!.
I traced it with difficulty to a faulty CD 4094 serial to parallel converter on the synth. board (u18). replaced with a new one and hey presto!.
I also took the opportunity to replace most decoupling tantalum caps with new LOW ESR electrolytics.

After I replaced the synth. I got the infamous BEEP BEEP BEEP, showing synth. unlock-(HORROR!) , and I retraced this to a badly seated coax that runs between the two synth. boards--(PHEW!)

73 de William
ZS4L
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ZS5WC
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« Reply #11 on: June 29, 2014, 11:47:29 PM »

  Grin Grin Grin
Got SECOND KWM-380 from an SK estate on Saturday!.
Now I guess I have the only two in Africa!.
Seems as a bonus this unit has most options fitted AND I have a CW narrow filter for it as well.
Cosmetically it also looks very good.

The work on no.1 continues, audio mods and capacitor replacements..
The new LOW ESR electrolytics are great-and has the same ESR values of new tantalum caps!.
I don't fancy tantalums for decoupling applications as they always fail SHORT and this causes other problems like feeding power where not needed thus blowing other devices, or shorting out high current supply rails.

For a rig this age, I am amazed by the stability of the PLL, also considering the very early 1st generation PLL design!.

I will update as work continues..

73 de William
ZS4L / ZS5WC
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