Superstar 3900 problem

[jazzsinger]

Thanks for clarifying... Christ I guess I better double check stuff before I end up putting a wrong part!

as Robb says, the 148 gtl and the 148gtl dx are two completely different beasts,even if they did come in the exact same box, no doubt both are great radios, but when it comes too badass, the 148 gtl dx is king, well here in the UK anyway.people will pay much more for a 148 gtl dx with a snake than a ss360fm (shrewd people buy ss360fm's), despite the fact its the exact same radio. they are legendary here.

i'm sure the tip42c won't go to waste, no end of multimode export sets they can be used in.

you wouldn't have been able to fit it by mistake anyway, the tip42c like the 2sa473 is a 3 pin device, the mb3756 is 8 pin inline.

like most things Uniden did, they found a cheaper way. As each new chassis evolved manufacturing costs were slashed, selling the finished product for the same or similar price to the previous model ensured profits rose at the same time costs fell, quality in some cases suffered but as they used cheaper parts it meant repair costs fell (well for parts anyway) i'm sure labour costs would be the same.

the downside is cheaper more simple repair parts mean more blowtorch merchants fancy their chances fixing things. which if your into buying/repairing radios may well be good, but if your just into buying with no knowledge of the repair side of things, it makes finding decent gear much harder.

 

[doffo]

as Robb says, the 148 gtl and the 148gtl dx are two completely different beasts,even if they did come in the exact same box, no doubt both are great radios, but when it comes too badass, the 148 gtl dx is king, well here in the UK anyway.people will pay much more for a 148 gtl dx with a snake than a ss360fm (shrewd people buy ss360fm's), despite the fact its the exact same radio. they are legendary here.

i'm sure the tip42c won't go to waste, no end of multimode export sets they can be used in.

you wouldn't have been able to fit it by mistake anyway, the tip42c like the 2sa473 is a 3 pin device, the mb3756 is 8 pin inline.

like most things Uniden did, they found a cheaper way. As each new chassis evolved manufacturing costs were slashed, selling the finished product for the same or similar price to the previous model ensured profits rose at the same time costs fell, quality in some cases suffered but as they used cheaper parts it meant repair costs fell (well for parts anyway) i'm sure labour costs would be the same.

the downside is cheaper more simple repair parts mean more blowtorch merchants fancy their chances fixing things. which if your into buying/repairing radios may well be good, but if your just into buying with no knowledge of the repair side of things, it makes finding decent gear much harder.

Appreciate the input. Really do. I did happen to see the 148 GTL DX on forums, but so far not in real life. Either way, just want a SSB rig that will do good.

 

[Robb]

Well I got a Superstar 360FM that needs work now.
No receive; no transmit.
The TX LED will not light when keying a mic.
There is no bias current at the final/driver.
Just some clues . . .

The pin voltages on the PLL are:
1 - 8.3v
2 - 4.3v
3 - 4.4v
4&5 - N/C
6 - 8.2v
7 - 8.2
8 - .2v
9 - 0v

See IC5 chart for comparison:
http://www.m0ysu.com/SS_360FM___Cobra_148GTL_DX.bmp

The first thing I noticed that is wrong with it, is that the VCO voltage will not adjust. It is stuck at 8v. L18 is supposed to adjust that voltage; but it doesn't respond at all. Of course, the VCO won't lock the first oscillator with this high voltage, as it requires 5.4v to lock.

Pulled and checked TR24 thru TR27 - they are all OK. The veractor diodes D31/D32 were tested too and they were OK as well. Also checked D33, D34 & D35. So, all of the semiconductors in that area were checked out.

Simple question: What causes the VCO voltage to go to 8v and lose the L18 voltage adjustment?

Another question for all the great radio gurus here to answer . . .

http://www.cbtricks.com/radios/cobra/148gtl_dx/graphics/cobra_148_gtl_dx_sm_pg33_34_sch.pdf

 

[Robb]

I found the fault with the PLL circuit being unlocked . . .

Turns out the three electrolytic caps that are in the VCO circuit (C93, 91, and 89) needed to be replaced. In particular, C93 was dragging down the circuit voltage. It had about 1/2 ohm of resistance and only 1/4 of its rated 100uf capacity. IOW - Toast. Changed it out to a 100uf/16v instead of the stock 10v unit. The other two caps were only a little bit off; so I just replaced them since they were already out.

I can key the mic now and the TX light comes on.

I aligned L17/L19 for peak output, the 1st oscillator freqs, the TX freq adjustment, and the VCO voltage so far.
Receive is really nice with an exception.
No AM receive; but SSB and FM receive works fine - weird.

There are more problems yet; the driver shows no current and the final current is very low.

I'll be reporting back with findings and more questions.
Hope some of you are all getting something out of this . . .

EDIT:
Pulled the final and driver out and tested them. The driver had no emitter voltage. Put new thermal compound on the new driver and old final and re-installed them. TX now works as it should. Set the bias on both transistors and then peaked the TX coils. Transmits fine on SSB and AM/FM. But still no AM receive yet; the S-meter shows no movement as well.
Still digging/no clue . . .

 

[jazzsinger]

I found the fault with the PLL circuit being unlocked . . .

Turns out the three electrolytic caps that are in the VCO circuit (C93, 91, and 89) needed to be replaced. In particular, C93 was dragging down the circuit voltage. It had about 1/2 ohm of resistance and only 1/4 of its rated 100uf capacity. IOW - Toast. Changed it out to a 100uf/16v instead of the stock 10v unit. The other two caps were only a little bit off; so I just replaced them since they were already out.

I can key the mic now and the TX light comes on.

I aligned L17/L19 for peak output, the 1st oscillator freqs, the TX freq adjustment, and the VCO voltage so far.
Receive is really nice with an exception.
No AM receive; but SSB and FM receive works fine - weird.

There are more problems yet; the driver shows no current and the final current is very low.

I'll be reporting back with findings and more questions.
Hope some of you are all getting something out of this . . .

EDIT:
Pulled the final and driver out and tested them. The driver had no emitter voltage. Put new thermal compound on the new driver and old final and re-installed them. TX now works as it should. Set the bias on both transistors and then peaked the TX coils. Transmits fine on SSB and AM/FM. But still no AM receive yet; the S-meter shows no movement as well.
Still digging/no clue . . .

check D26,D27 (AM detector diodes) TR23 (AM DET SWITCH) for AM receive, TR13 (AM S Meter switch) and VR1 for s meter if its just not reading on AM/FM. if its not reading on all modes check D14

 

[Robb]

Thanks George . . . I'm on it . . .

 

[jazzsinger]

Thanks George . . . I'm on it . . .

hope you get it going mate, its a quality radio,best left standard 120 ch though.

 

[Robb]

You were right for telling me to check the AM transistor/diodes first. I should have done that.
They all checked out fine.

But in the process I did notice that the AM/FM squelch adjustment pot on the board is not working. SSB squelch works. So; I should test the pot/VR4 on the board next.

 

[jazzsinger]

Preset potentiometrs\Vr's are a common problem on that board,they get moved about by the screwdriver wizards all the time and become fragile/intermittant,add to that the age of them and you have a common problem,you'll find the front panel controls can go the same way too.

 

[Robb]

I don't have a new 50k pot/VR to replace it with.
I'll have to get one tomorrow in the morning.

Also going to make a list of all the 10v electrolytic caps in this radio - and replace them.

On another note, isn't the best way to track down a receiver flow problem is by using signal injection? Don't know how to do that yet; but I do have an HP 8656B signal generator that I picked up for a song just the other day. I'll bet that it can make short work of tracking down the faulty receive part(s). My next step is to learn how to do this.

 

[Robb]

I didn't find the exact fault; but I fixed it . . .

Said I was going to change a bunch of caps out on mt last post. All of the 10v caps were replaced with 16v caps - about a dozen or so. When I turned the radio on after changing them out (took about an hour +/-), AM mode was now receiving/working once again.

Many of the 47uf/10v caps removed - then tested - were well below or at half their rated uf values.
Woof!

Since this radio is a mid/late 80's vintage and two caps were found faulty already; I would have to say that it is probably a great idea if I just went ahead and changed the rest of the caps out too. Why wait for that to happen again? Wondering just how many more caps left in the radio are on the borderline of failure right now.

Put the HP freq generator on it and aligned the receive and set the S-meters for 9 S-units on SSB and AM.
Works perfect so far . . .

EDIT:
Hey Jazz/George; just how do you turn the ch 9 switch into a +10kc?

 

[Robb]

The list of the last bunch of cap replacements:

1uf/50v - .87uf
10uf/16v - 10.5uf
4.7uf/25v - 4.5uf
10uf/16v - 7.7uf below specs
10uf/16v - 10uf
2.2uf/25v - 1.9uf
1uf/50v - .9uf

I'll be adding more . . .

EDIT:
Few more notables . . .
10uf/16v - 7.7uf below specs
10uf/16v - 5.9uf below specs
No doubt - that last entry was about to FAIL

 

[jazzsinger]

EDIT:
Hey Jazz/George; just how do you turn the ch 9 switch into a +10kc?

been a while since i did it Robb, but if i recall you remove jp54 next to ic6 (cd4008 binary adder) which grounds pin 9 of ic6, the carry in pin, once you remove the jumper, if you wire the centre of the ch9 switch to the empty hole that goes to pin 9 of ic6, then wire the bottom of the ch9 switch to the other hole that was tied to ground or any other ground, you then wire the top of the ch9 switch to 8v, the main regulator 2sa473 is a good place to source that. the theory being you control the carry in pin which is normally tied to ground, which adds an extra 1 to the n code when its switched high.


doing it that way using the existing jp54 board holes and using similar wire to whats in the radio it means you only have one wire that looks out of place, you might even find an unused hole in the 8v track coming from the centre pin of the regulator (i just can't remember, too many sweet mary janes since i last did it). with so many radios that do the +10khz jump i don't see the point in doing it too a classic radio anymore, same as i don't see much point adding extra bands to it.

 

[Robb]

I have no interest in putting in the extra bands. But the CH9 switch was already hacked for the roger beep before I got it. So I figure that taking out the roger beep and putting in the +10kc mod and making all of the channels available within the radio's range would be best. I think that would be most useful to the radio.

I found this link; perhaps you can tell me if its contents are correct for the +10kc mod.
Don't want to do anything to the radio until I am sure.

COBRA / S-STAR 010 CHASSIS

10KC Shift - Remove JP54 and put a 4k7 resistor in its place (located by IC6), then connect a wire onto pin 9 of IC6. Run the other end of the wire to a switch - then to a suitable 8v supply on the board. When the switch is thrown the rig will go up one channel (10KC's)

Cobra 148 Page

 

[neotof]

Replaced tr51,52,49,35,39 and d91.

bonjour j'ai problème presque identique mais en ssb
tr52 est un 945 in it an the scheme called for a 471 there.

bonjour, tr52 j'ai 2sc945 il deviens Chauffé en Ssb rx, et la puissance hf ne dépasse pas 10 watt alors que sa devrai être 20 25 pour un 3900HP

help