President lincoln display/audio fault

[sparky7083]

Radio Make and Model: President Lincoln
PCB Number:
PLL Number:
Test gear available: volt meter
Symptoms:I have a Lincoln...freq display has nothing on it, and there is very little or no audio from speaker..there is a small crackle when switched on but thats it...I had this radio given to me so I have no history about the radio....I`ve had the tops off the radio, and it`s had a repair done to it..there is a wire from the large chip which then goes to the speaker...never seen this before, and I`ve had a few Lincolns.....I can send photos if anyone wants them...hope someone can help....this is my first visit to a forum, so hope I`ve done things right
What is working:It lights up

What has been tried: Nothing as yet

Did it suddenly happen ?: fault on radio went it was given
Anything else that may be of help?:

[The Defpom]

There should not be a connection from the MPU (the large chip) to the speaker, are you sure it is soldered, and the wire has not just come off and lodged between a couple of pins ?

Lincolns can be hard to troubleshoot, I have repaired many of them, it usually requires a frequency counter and oscilloscope to be able to troubleshoot the MPU PCB, especially if someone has been playing around inside the radio, you never really know what could have been done, or shorted out.

At the worst, I would be interested in buying it off you for parts, I have a couple of units here which need parts to get them going.

[sparky7083]

Hi ya Scott
the wire to the mpu is soldered (defo)...thought it was strange to see it....I`ll keep on with it for now, and see how I go..!..do you have a good copy of a schmatic for this radio...the ones I have down loaded are sh#t
regards
Daz

[zodiac]

That doesn't sound too healthy to me, I think it'll be coming your way very soon Scott.
Dave.

[sparky7083]

Come on folks........I was told this was the top web page to get excellent info and help from.....so far I`ve had nothing really ..only an offer to buy my radio....If I`d wanted to sell the radio I`d would have gone on ebay.....so come on people, lets have some help please .
best regards
Daz

[The Defpom]

The MPU PCB is a complex thing, without suitable test gear you stand no chance of locating the fault, at the very least you would need to determine what is working correctly on the PCB (if anything), you need to check the frequencies and control signals of the VCO's, and also the digital waveforms coming out of the MPU (which you need a scope to see), you stated the only test gear you have is a voltmeter, well, you need a lot more than that to work on a MPU board for a radio like this, without the test gear being available, there is nothing I can do to help you, it is not that I don't want to, but anything I would suggest involves using test gear you don't have.

[sparky7083]

thanks for the reply....I`m going to try and borrow some test gear...so watch this space
best regards
Daz

[sparky7083]

Hi ya guys
up-date on Lincoln...I`ve got the display working and it now transmits and recieves....But I still don`t have any sound coming from speaker. Only get a small crackle when set turned on...fi roger bleep is switch on you can hear a very small bleep from internal speaker....Anyone any ideas??????

[The Defpom]

Hi,
What did you find to fix the display ?

If there is no audio in all modes then it is something to do with the last signal or amp stages.

If you have a RX signal with no audio then at a guess the squelch amp may be shorted out, check IC101 (NJM2902) on the main PCB slightly right of center towards the rear, if it is warm then it is shorted out, if it feels OK then it probably is OK, usually when these fail they get warm. (sometimes the signal meter will also show a constant signal when this part fails).

It could also be the audio amp IC103, (TDA1905, on the left towards the rear with the small metal heatsink soldered to it), I have had them partially fail, where they would produce the click at turn on, and even some hiss, but no RX audio.

Other candidates to check are Q135, Q109, both 2SC945.

[sparky7083]

Hi ya
I replace a cap on the MPU board...It was next to the 5 volt power regulator....I fitted a slightly higher voltage one but works fine now
regards
Daz

[Warf135]

Here is better quality schematic for HR2510 (lincoln):

hr2510(lincoln)sch.gif

(581.54 KiB) Downloaded 306 times

And here is a nicely re-drawn Schematic of the CPU board
Drawn by Rick from Euro Radio Co.

uniden_hr2510_cpu_sch.pdf

(373.85 KiB) Downloaded 1178 times

Hope these help!

[sparky7083]

Thankyou for the schmatics.......there grrrrrreat

[Warf135]

Your welcome Daz, hopefully you will be able to get the radio working now.

In a previous post you mentioned a wire soldered from the large chip to the speaker. does the speaker also have the 2 normal wires going to it? and what is the number on the "large chip"?

[sparky7083]

Hi ya Norm....the wire from the chip went to one side of the speaker and the other side of the speaker went to earth...when I get a min I`ll get the number off the chip....thanks again Norm
regards
Daz

[Warf135]

hmmm interesting, it looks like possibly the original speaker wire came off and this new wire has been jumped in to get it working. I'm wondering wether the wire is going to the correct place..

If possible, when you look for the number on the big chip, see if you can tell which pin/leg it is soldered to (pin 1 indicated by an indentation)

UPDATE I've just looked at the schematic and the speaker should connect to ground as it is, but the positive end of the speaker should be going to pin 7 on the 9 pin mini-molex accessory plug on the lincoln. This is then linked to pin 1 on the mini-molex connector by a loopback plug. if your radio does not have the loopback plug on the back solder the speaker wire direct to pin one on the mini-molex.

From pin 1 on the mini-molex the speaker wire should then go to the PA switch, and only after all that should it then head towards the Amp chip (IC103 - TDA1905)... so if your lincoln has a wire going direct to a chip, its definately wrong

[sparky7083]

hello again Norm
sorry took so long to reply, we`ve had a new arrival in the family....so I`ve had a lot of late nights..lol..
anyway the number on the big chip is :::: HD4074008S....the wire to the speaker was soldered to pin 34...
hope this helps
best regards
Daz

[Warf135]

Hi Daz no worries on the slow reply.

That wire is definately on the wrong place, and thats why your getting no sound from the speaker. The speaker should not connect anywhere near that chip. I could not locate that chip on the schematic, but the datasheet for it states its some type of processor and not an amp chip.

Remove the wire from there and connect it to pin 7 on the mini molex plug at the back of the radio and see if you get sound.

[sparky7083]

Hi ya Norm....I`ve tried what you suggested...still just get the crackle an then a hiss when switched on...I`ve gone direct to the board were the mulit plug wiring goes too, and then to the earth....still no joy....is there an easy way to test audio circuit...????
regards
Daz

[Warf135]

I dont know of any real "easy" way to test the audio circuit... If you had a scope you could check for audio at the input and output of the audio amp chip to confirm if its blown or not or check the voltages at the pins of the the audio amp chip. It sounds as if the audio chip (TDA1905) has probably blown to me, although I've only worked on a couple of these Lincolns, so I may be wrong..

If you had a bad capacitor on the MPU board, there may be other bad caps around the audio amp chip. Bad capacitors are common in the Lincoln from what I can tell

[sparky7083]

High ya Norm
I`ve done some checking and found incorrect voltages to the chip IC101 (NJM2902) they`er high readings from pin 1 the power voltage is ok,,,I think this is the squealk chip....explained earlier in this question page ....not sure were to go now.
regards
Daz

[Warf135]

If there are incorrect voltages at many of the pins on IC101 then it could be blown... do like scott suggests earlier in the topic and feel if IC101 is getting warm as thats another indication that its blown.

If its just one pin of IC101 showing incorrect voltages the fault is probably external to the chip.

Here is Ebay link for NJM2902N if you need to get a new one:-
http://cgi.ebay.co.uk/2PCS-NJM2902N-290 ... 45f3fb8fea

[zodiac]

Norm,
That's expensive, I get mine from Chris at Mode Components in Birmingham, 40p plus £1 post for the LM2902N.
He also has the audio chips TDA1905 at £1.25, and that includes vat.

Daz,
For what it costs I'd change both IC's, remove the copper heat sink from the audio IC first.

[Warf135]

@Dave, Thanks for the info..I never even heard of Mode Components before, but now I shall be using them for sure!

[sparky7083]

Thanks for your help guys...
I`ve ordered both the chips as advised,,,,,so we`ll see what happens when they arrive
thanks again
best regards
Daz

[sparky7083]

Hello guys
just had some bad news , mode components can`t supply me the chips, does any one have any other ideas where to get them from apart from ebay
regards
Daz

[zodiac]

That's bad news, I used my last audio chip only last week, has he closed down ?.
Knights CB have them but not as cheap.

[sparky7083]

no matey he`s not shut down..just doesn`t have any in.........gutted....