Yaesu FT221 problem with alignment

[ontheedgeandy]

Tried that but still no joy any other ideas? The mic audio is very quiet also even with the gain right up.

[Radio Wrangler]

Could the gain right up be overdriving the VOX and causing the sticking in TX mode, but a fault in the modulation drive to the varactor be causing the RF to have very low deviation? High value resistor gone extra-high or a capacitor gone short?

david

[ontheedgeandy]

Originally Posted by Radio Wrangler

Could the gain right upbe overdriving the VOX and causing the sticking in TX mode, but a fault in the modulation drive to the varactor be causing the RF to have very low deviation? High value resistor gone extra-high or a capacitor gone short?

david

the set keys then unkeys ok fine at first but low mic audio, then if u just leave the set on its own the receives starts to drop off and then on its own it keys up, let the set cool down and it returns to normal again except for mic audio, ive noticed also as this happens the receive audio drops to nothing

best regards Andy m6yyd

[ontheedgeandy]

Originally Posted by ontheedgeandy

the set keys then unkeys ok fine at first but low mic audio, then if u just leave the set on its own the receives starts to drop off and then on its own it keys up, let the set cool down and it returns to normal again except for mic audio, ive noticed also as this happens the receive audio drops to nothing

best regards Andy m6yyd

ok so solved the stuck in transmit function was dirty potentiomenter that controls the threshold for vox, but cant figure out which components i need to look at for the low mic audio now

[Radio Wrangler]

Service info should give you normal audio voltages at various places along the chain. Speech isn't a steady enough level nor is whistling. There are apps for smartphones which will make audio tones, but the headphone jack levels will be too high for a microphone input, so you'll need an attenuator (three resistors)

Then you'll need something to measure the level with... oscilloscope, audio millivoltmeter etc.

The likelihood is that some component along the chain is sulking there is a steady failure rate of transistors, capacitors and resistors. These things were built with cost-competitive components... mind you, some of the o ce premium components didn't fare much better. Electrolytic capacitors use water-based conductive fluid in them as one of their electrodes. Over time water leaves as vapour past the seals. It just needs a slightly iffy rubber seal or a bit of muck and they fail without needing high temperatures to accelerate them.

So it's simple spadework. Apply a signal and follow it along, checking levels, to get the fault down to an area, then start focusing in on the problem.

The audio path may have some AGC to correct for microphone levels, there may be a compressor or speech processor. So it may be a bit more complex than just a couple of amplifiers and a gain pot.

One quick check would be to substitute a known good microphone. You never know.

David

[ontheedgeandy]

Originally Posted by Radio Wrangler

Service info should give you normal audio voltages at various places along the chain. Speech isn't a steady enough level nor is whistling. There are apps for smartphones which will make audio tones, but the headphone jack levels will be too high for a microphone input, so you'll need an attenuator (three resistors)

Then you'll need something to measure the level with... oscilloscope, audio millivoltmeter etc.

The likelihood is that some component along the chain is sulking there is a steady failure rate of transistors, capacitors and resistors. These things were built with cost-competitive components... mind you, some of the o ce premium components didn't fare much better. Electrolytic capacitors use water-based conductive fluid in them as one of their electrodes. Over time water leaves as vapour past the seals. It just needs a slightly iffy rubber seal or a bit of muck and they fail without needing high temperatures to accelerate them.

So it's simple spadework. Apply a signal and follow it along, checking levels, to get the fault down to an area, then start focusing in on the problem.

The audio path may have some AGC to correct for microphone levels, there may be a compressor or speech processor. So it may be a bit more complex than just a couple of amplifiers and a gain pot.

One quick check would be to substitute a known good microphone. You never know.

David

thanks for this excellent advise i will be on the look out for a second hand osciliscope and a few other peices of test equipment, but for now ive managed to order a working board of ebay which im awaiting receipt of. once ive got the test equipment i will continue to figure out the problem, i beleive i may well have destroyed a transistor or ic LD3001 which is obsolete with the soldering iron when removing and replacing the electrolytic capacitors.

[ontheedgeandy]

evening everyone, would anyone have any ideas what transistor the one in this circuit is or what i could use to replace it, thinking about creating the above circuit on stripboard to replace the LD3001 IC mic pre amp circuit.

Best Regards Andy

M6YYD

[Radio Wrangler]

You should be able to get away with murder with that transistor.

Something with high Hfe at a few mA and a reputation for reasonably good noise. Something fairly jellybean 2N3904/MMBT3904 in through-hole or SMT formats is a jack of all trades.

In circuit complexity terms going to an opamp isn't going to be any easier. I'd just stick with the original circuit.

David

[ontheedgeandy]

Originally Posted by Radio Wrangler

You should be able to get away with murder with that transistor.

Something with high Hfe at a few mA and a reputation for reasonably good noise. Something fairly jellybean 2N3904/MMBT3904 in through-hole or SMT formats is a jack of all trades.

In circuit complexity terms going to an opamp isn't going to be any easier. I'd just stick with the original circuit.

David

It looks like it's the ld3001 ic which is basically that circuit so I've built a strip board version based on the transistor you recommended to put in replacement of the obsolete ic,

See the pictures of the board I've created what do you think
Best regards andy
M6YYD

[Radio Wrangler]

Given that circuit and the size of the thing, it was probably a hybrid... an SMT transistor Or chip transistor, chip capacitors and thick film resistors fired on a ceramic substrate.

There was a fashion for sticking common analogue circuits on them, but the predicted advantages and cost savings were proven a bit optimistic.

David

[ontheedgeandy]

Originally Posted by Radio Wrangler

Given that circuit and the size of the thing, it was probably a hybrid... an SMT transistor Or chip transistor, chip capacitors and thick film resistors fired on a ceramic substrate.

There was a fashion for sticking common analogue circuits on them, but the predicted advantages and cost savings were proven a bit optimistic.

David

Would you say that this would be ok to solder in to the board as a direct replacement for the original ic?
The other components capacitors etc are allready around the ic on the board as through hole

Best regards Andy M6YYD

[Radio Wrangler]

Ought to be fine.

David

[ontheedgeandy]

Originally Posted by Radio Wrangler

Ought to be fine.

David

Thankyou I will try replacing this later and let u know the outcome