The Defpom Forum, for RadioMods, S&M Software and Music by The Defpom

absorbentgnome

Changed CPU over, all working now :)

Method used for desoldering:

IC removal done with hot air station at about 330oC for each side of the chip, levering it out slowly from either side. A lot of heat, time and patience is needed to get the board up to temperature to weaken or melt the solder for a ...

absorbentgnome

Hi Scott
Thanks for your reply. The resistor array checks OK. When the CPU comes I'll post back here if it fixed it or not. Soldering on the CPU looks absolutely perfect, no bad joints, board is in immaculate condition with no corrosion. On your advice, I will check the thru holes associated with ...

absorbentgnome

Thanks for your help zodiac, have tested between known good transceiver and this one and have come to the conclusion that the processor is damaged.
Hopefully a replacement will be on its way soon.
Dan.

absorbentgnome

Ok thanks Zodiac

There are solder marks on those components, so it probably has been done before.
Have you seen inoperable front panel buttons before?
Dan.

absorbentgnome

Radio Make and Model: President Lincoln
PCB Number:
PLL Number:
Test gear available: Multimeter, scope, counter, sig gen
Symptoms: No response from band, channel, indicator buttons.

What is working: TX ok when keying mic. Frequency dial OK.

What has been tried: Checked operation of buttons and ...

absorbentgnome

Brilliant thread, well done Pioneer621 for finding the problem!

absorbentgnome

I just repaired one of these recently. The construction of it is really a pain in the arse.

Don't suppose anyone has an ammeter out of one of these?

absorbentgnome

I'm looking for an ammeter panel meter from a Manson EP925/Palstar PS30 power supply. Can anyone help?
Sadly the original meter has been damage beyond repair.

absorbentgnome

I just recently re-worked one of my pro-510s.
I installed variable power,along with several
other mods..The radio now,will dead key anywhere
from 0 to 5 watt dead key and swing up to 20.
Radio checks are all great.Loud clean audio.
Everyone thinks i am talking on a connex or galaxy.
changed final ...

absorbentgnome

Hi sinstp

First check the loudness of your modulation on another cb, and note how you are most probably not bleeding over onto adjacent channels at the moment and the audio is clean. If the cb you are listening on has poor filtering and you are getting bleedover then get someone further away to ...

absorbentgnome

http://n6tr.jzap.com/850repair.html

1 of many?

Indeed - I have replaced a number of caps on this rig. Luckily, someone else had already replaced the caps on the CAR board before much damage to the pcb was done. (its the one with the early DDS chips - got my fingers crossed for these ones!)

I ...

absorbentgnome

The problem does seem better now. The cap C124 is across the 6V supply in the MC3357P circuit. Has anyone seen any effects of this cap drying out on a MC3357?

Since its across the supply rather than in the functional part of the circuit I would have thought that it could have lost a lot of ...

absorbentgnome

Replaced cap C124 (underside was swollen and had reduced from 22uF to 15uF) on IF board and hoped for the best. Took a while for the problem to show itself but it was still there.

So I connected up my other kenwood with an antenna switch so I could definately check the problem was still there ...

absorbentgnome

Checked the receiver under low noise conditions and its fine.

A further problem has surfaced though - in FM receive mode, the AGC seems unstable. The signal fades and returns in an oscillating manner which is slow, then speeds up then slows down again. This affects signals around the S9 level and ...

absorbentgnome

Heh good post Dennis.

I am in no way suggesting that experimentation with your radio is wrong. After all getting in there and modifying/uprating/improving sucessfully proves that you've understood the circuit design and used the theory to calculate new values for the appropriate components.

The OP ...

absorbentgnome

Ok thanks for the information Rick. I'm going out into the wilderness this weekend so I'm going to take the TS850 and a few other rigs and compare the sensitivity and quality in a low noise environment. It may not have a problem.

It maybe worth checking VFO input on Gate G1 of Q9, as I remember ...

absorbentgnome

I've never understood why you would want to swap around the finals in a radio just to gain an extra watt or so. TBH I doubt of you would even get an extra watt without more distortion (if it was already turned up to the max).

Surely its better to run the radio within spec so you don't overheat the ...

absorbentgnome

When I compare the SSB audio quality between my Icom 735 and my TS850, the TS850 seems more susceptible to noise. The 735 just sounds better and seems to reject the noise more. The audio tone is turned down on the 735 but there just seems like there is much more noise on the TS850 for that to ...

absorbentgnome

Hi Rick, its been a little while! Hope things are ok with you :)
Been really busy with new job here so there hasn't been much time for fiddling with radios :(

John - If you google the varicap part number (KDV251S) that is on the circuit diagram you should be able to get a datasheet for it. It is ...

absorbentgnome

Hi there intercept

The channel display flashes if the PLL is unlocked. The PLL is at the bottom left corner of the main PCB with the radio facing towards you.

The varicap diodes can sometimes fail causing this, I had a Maycom that would not lock on the lower channels until they were replaced ...

absorbentgnome

Never used a Mac, apart from the old 68000 ones.

I used to love computers, I had an old Acorn Archimedes with an ARM RISC processor which was awesome for programming and doing 'cool stuff'

Computers now tire me a bit, becuase of the power and resources they have and how they're wasted to give a ...

absorbentgnome

Does the cobra have high swr output protection? Could be that its kicking in (i.e. reducing the output power) early due to some problem or effect between the radio and the amplifier. Just a guess unfortunately. Is the audio recieved on another rig distorted at all?

Isn't 3 watts dead key with 20 ...

absorbentgnome

I have finally had enough of Windows. My ebay account got hacked because I had been infected by a rootkit and keylogger, from an unknown source. I am very careful about what goes onto my computer and know how to remove nasties by hand etc. Also use Opera instead of IE and all the rest. This rootkit ...

absorbentgnome

^^^^
What these guys said

absorbentgnome

Sounds like the power supply in a desktop computer, to me.
Ferrites may help reduce the interference, but I wouldn't put money on it eliminating it.

Yeah probably.

Our TV gives out a little interference, I tried ferrite rings on the mains lead and on the scart lead and it made no difference at ...

absorbentgnome

A question about verticals.

I have seen people selling modified CB antenna (http://cgi.ebay.co.uk/RESONANT-VERTICAL-ANTENNAS-FOR-80-40-OR-160-80-MTRS_W0QQitemZ270165324961QQihZ017QQcategoryZ4672QQssPageNameZWDVWQQrdZ1QQcmdZViewItem) with what looks like additional loading coils placed at the bottom ...

absorbentgnome

Sounds like a missing internal supply to me, but unfortunately I am not familiar with the radio chassis. The audio chip supply and RF output transistor supply are often linked, so check for an open resistor or fried track. Even if the audio chip is dead, there still should be some kind of TX if the ...

absorbentgnome

I have a question about the Noise Blanker on this rig.

How can I test its operation? It doesn't seem to do much at the moment, the only effect i can get it to do is make the sound distorted on a strong signal am station.

absorbentgnome

Excellent news!

Before ordering all the new caps, I had one final go at trying to find the problem.

I tested the PA unit using many silly but workable ways of affecting the filters like putting a screwdriver in the air cores that form part of the 22-30Mhz filter. Could not get any variation in ...

absorbentgnome

Yeah I had that problem too. The noise is the audio chip on the right of the rig oscillating.

After cleaning it up it had to dry out really well (hairdryer?) before the audio worked properly. Make sure you get all the conductive corrosion crap off and its nice and clean. It corrodes the underside ...

absorbentgnome

I replaced it with a 0.22F memory backup capacitor from Rapid. It stores your settings for about 5 hours, not as good as the battery but hey it doesn't leak acid all over the pcb when you leave it discharged for a while.

http://www.rapidonline.com/productinfo.aspx?tier1=Electronic+Components&tier2 ...

absorbentgnome

Has anyone had good results from putting snap-on ferrite cores onto the mains leads of equipment that causes interference?

absorbentgnome

Checked the driver and final bias and they were ok (110mA, 780mA). Adjusted them back to 100mA, 600mA.

As far as I know, this hasn't previosuly been owned by a CBer (apart from me of course). There are no obvious signs of overheating.

I have checked the operation of the relays by listening to them ...

absorbentgnome

Ok thanks for your advice Rick.

The performance is similar on all bands, however to be fully sure I need to get myself a dummy load capable of 100W. Or, an antenna matcher. I certainly don't want to risk further damage by raising the power on an unmatched longwire or silver rod.

Will check the ...

absorbentgnome

Tried to find which inductor was sensitive but it didn't work. Rig TX's more power when the PA is uncovered and in a certain position. Didn't manage to get the full 100W this time, more like 60-70. At least the output transistors are ok

Definately sure this isn't dry joints.

absorbentgnome

I nabbed a faulty Icom 735 much to my excitement and went about fixing the problems with it.

0. Dry joint on antenna wire on filter board - fixed by previous owner and checked ok
1. Cracked pcb track on recieve phono connector - fixed
2. PLL unlock until warmed up for a little while - very slight ...

absorbentgnome

and this, beware the switching noise!

http://www.hanssummers.com/radio/psu/index.htm

absorbentgnome

Have a look at this:

http://www.qrp4u.de/docs/en/powersupply/index.htm
http://www.webx.dk/oz2cpu/radios/psu-pc1.htm
http://www.users.on.net/~endsodds/smps.htm

absorbentgnome

Ok not as fixed as first thought. Slowly, the squelch stopped working. Perhaps I disturbed an intermittent component with the heat of the iron.

Now fed up, I brute forced the squelch control into the circuit, which lo and behold got it working properly.

A 100k resistor was connected from the ...

absorbentgnome

Fixed!! :D

You would not believe it. The fault was an original manufacturing defect - the squelch never worked on this in its life! Scattered around the board were some solder through holes, one of them had not made contact with the other side of the board, although it was soldered.

Exactly how ...

absorbentgnome

To see if recieving a signal affected the voltage at pin 12 it did. Recieving a strong signal caused the voltage to fall from 0.3V to 0.11V.

absorbentgnome

I double checked the voltage from the pot contact, it varied from 0 to 3.3V. There is a reistance measured between the contact and pin 12 of around 11.5k. The voltage at pin 12 varies from 0.18 to 0.4V, which is low. The squelch pot is 50k.

absorbentgnome

The supply at pin 4 is 9.38V.

I swapped the MC3357 IC and there was no change, and the IC works in the other unit, so the chip is OK.

The squelch pot is ok too, approx 3V is across the pot and the pot contact voltage varies in the same manner between the two units.

I experimented lifting the ...

absorbentgnome

R10, R11, R14, R18, R19, R20, R22, R23, R25 check ok

absorbentgnome

Nope that stab in the dark didnt work.

Its also definately not the MC3357P, swapping them had no effect.

absorbentgnome

There is a small glass signal or detector diode nearby, D1. The working one has a forward voltage of 350mV.

The faulty one has a forward voltage of 470mV - I will try swapping them.

absorbentgnome

Some measurements from the MC3357P

Working unit

Squelch Pin 11 12 13
Full off 0.2 0.16 8.58
Full on 5.3 1.3 0

Faulty unit

Squelch Pin 11 12 13
Full off 2.12 0.17 8.75
Full on 2.11 0.36 8.75

So quite clearly not working, hmm but why?

Something to do with filters Z1 and Z2 on the datasheet ...

absorbentgnome

Ah no the squelch circuit is in the MC3357, hopefully the datasheet will allow me to find whats wrong.

absorbentgnome

Hello again

I have two TRC-1007, fixed one and it works nicely. The other one almost works. TX and RX is fine, its just the squelch control doesn't work. It never cuts out the fm noise.

Does anyone have a circuit diagram for this radio? ( Rick? :) )

I assume the LM358 at the bottom of the pcb by ...

absorbentgnome

Use the diode test function on your multimeter to measure the forward voltage across the diode. You should get around 500mV for it, if the diode is short then you will get a low reading. If it is shorted, then the linear has been connected in reverse without a fuse.

Download the datasheet for the ...

The Defpom Forum, for RadioMods, S&M Software and Music by The Defpom

Search found 82 matches

Re: President Lincoln control buttons not working

Re: President Lincoln control buttons not working

Re: President Lincoln control buttons not working

Re: President Lincoln control buttons not working

President Lincoln control buttons not working

Subject: Test Your Knowledge (President Lincoln/HR2510).

Ammeter for Manson EP925/Palstar PS30

Re: 850

Re: Question about receive quality on a TS850.

Question about receive quality on a TS850

Windows woe

Modifying a silver rod for operation on 80,40,20 etc

Icom 735

Realistic TRC-1007 Squelch problem