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What are general thoughts on a Malaysian Cobra 148?

guitar_199

Sr. Member
Mar 8, 2011
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Deer Park, TX
Through a friend of mine I just made a deal on one of these for $60 plus shipping. I am still in the first week from knee replacement... so have not hooked it up yet. I was told that shortly before it was shipped to me the owner did a net using the radio and that it sounded good.

So .... like I say..... just looking for what folks think about these.....
 

Dmans

Sr. Member
Jan 22, 2017
1,344
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Georgia
I have one. After removing the (required(?) blue meter LED) and making repairs to eliminate the Golden Screwdriver hacks, it works quite well with great receive and clear transmit audio. Not a power monster and was never meant to be. The only modification it has (now) is an unlocked clarifier.

I think I have about $25.00 wrapped up in it. And yes, I would do it again.

73
David
 

Low_Boy

Sr. Member
Jan 21, 2010
1,880
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Rochester N.Y.
I have had them and I have had Taiwan 148 GTL's. For some stupid reasons I like Taiwan radios better. Stupid reasons Nicer covers on the Taiwan radios and bigger crystal, I an off hand I do not remember the X number of the crystal. Other than that they both work about the same. I do not like the front microphone version though.
 
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loosecannon

Sr. Member
Mar 9, 2006
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i believe it's the malaysian models that need to have that jumper wire mod done where you tap off power before the power choke and send it to the audio chip and driver/final section IIRC.
LC
 
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Dmans

Sr. Member
Jan 22, 2017
1,344
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Georgia
I did perform the mod below (copied and pasted from ???) to mine and it did wake up the SSB audio. No channels, no NPC, no RWOB, no other mods and radio performs great.

Cut trace on PC board between Pin 1 of IC6 and pin 2 of IC4 ( MB3756 ). Next, install a .1uf mylar
capacitor at C136 and a jumper wire at J44. This corrects distortion on the SSB transmit audio


73
David
 

Handy Andy

Do Your Research First, Then Decide...
Apr 23, 2018
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Be sure to locate the L501 (L18) / R138 - PLL 8V feeder, goes to Pin 9 which in OEM per Tiawan and previous (including Philippines) they use an actual FERRITE Bead at the spot.
1662297291099.png
L501 (L18) is a simple jumper and ferrite LD077 - and C84 is the 1000uf Electrolytic cap right next to it.

In some 148 boards, it's not even labeled - it's a resistor - usually 100Ωohm resistor - it (power) comes from C84 - thru this resistor - into Pin 9 - so if the distortion is fixed but still have warble- this spot is the problem - the PLL struggles to regulate the loop varactor voltage when the radio swings in SSB mode.

A ferrite bead usually helps keep the PLL from fighting its own internal squealing caused by lack of RF off the power feeder. The Electrolytic cap is not helping matters any, but it's needed to keep the spikes from the swings from causing more regulation problems at the PLL. - the use of that power supply filter design using the ferrite explains the purposes of that choke / Ferrite bead.

They used a resistor to tame down issues other than to generate the warble, which was a feeder line issue of an RF loop in the power supply itself. The Pins 1-2 and 3-4 were those gates the PLL injected or subtracted power from the Varactor circuit (pin 5 result) - they didn't want it going out of band or off frequency too far, so they installed the resistor to make the Pin 6 LOCK more sensitive by constriction.

When these first came out they used their RCI8719 chip from Malasia. It was one of their first run designs using their chip versus the Fujitsu one most associated with the 148.

The Resistor lowered the power supply consumption to "starve" the squeal issue but then presented the warble - so the bead usually helps with this warble problem - the squeal is similar to a "ring" effect that can affect lock - which if that comes up - then you have to swap out the chip, the OEM-type (RCI8719) can go bad or was built (born) bad to begin with so they fixed the squeal issue by starvation of the chips power supply feeder to send more of these known faulty boards out, they worked for most people that only used AM not best for SSB.

They did well as long as ALC/AMC and Limiters were installed - lord help us when they removed or disabled them, they really messed up a channel.

  • - but if you listened to them carefully enough - their AM side also ran into a Varble - a variable sound effect those listening in SSB mode could hear that radio produce while it's in AM mode - it was a mixture between the AM and what sounded like FM because of the PLL trying to correct or apply to the varactor with what little power it had left to pull from the power supply constriction that resistor presented.

These boards also used a 3756 chip that was not the best at regulation - so the power supply split to lessen the losses from the power choke draw and it doing it's job - fixed one type of problem but you still may have the board with the chip of their firstborn RCI8719 types that would have Lock issues and sounded terrible on SSB - even if the mic gain was backed down - the peaks pulled too much from the Choke / 3756 combo - enough to drop it and lose lock.

So, raising the voltage at the PLL when it's under load to regulate (like TX mode is) gave it enough power to track better - which also worked in the favor of the channel expansion - which required even more power swings that if the resistor was left in there - it could not accomplish.
 
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