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To anyone who has adjusted the bias on an Anytone 6666......

Lkaskel

Well-Known Member
Aug 4, 2017
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Hi Gang,
On the bench tonight is an Anytone 6666 with blown FET's (13N10's). I will be replacing them and will want to adjust the bias if needed. There are 4 - 13N10's and 3 variable resistors in the amp section of the radio.

upload_2020-7-28_22-33-8.png

If you have adjusted the bias on this radio which adjustment points did you use? I would love a schematic or alignment procedure but all I am looking to do is be sure to set the bias correctly. I will also be replacing the 2 caps that Lester suggests.

Thanks as always!!!!
 
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When you unsolder the 'FET's - Back probe the Gate lines of the Finals - it is my fear they tie both to one, but they use diodes to feed into each one separately. (#3) the "header jumper" like you'd use for PC - is the mA "draw" test jig. Positive lead to pin that goes to front panel (Down in photo) Upper pin is their Feed - Negative lead goes there.

For my own sake I set mine for 30mA ON #1 and #2 but set #3 to 55mA and leave it. Runs the coolest for power trade off - if you find power sinking - dropping - STOP - recheck the mA draw, these are VERY temperamental..

Something doesn't look right in that photo - you should have another set of headers - one for each Variable - the headers closest to the variables by their respective FET's - Your first one is pre-driver (#1) - Driver (#2) and finally the #3 finals.
 
When you unsolder the 'FET's - Back probe the Gate lines of the Finals - it is my fear they tie both to one, but they use diodes to feed into each one separately. (#3) the "header jumper" like you'd use for PC - is the mA "draw" test jig. Positive lead to pin that goes to front panel (Down in photo) Upper pin is their Feed - Negative lead goes there.

For my own sake I set mine for 30mA ON #1 and #2 but set #3 to 55mA and leave it. Runs the coolest for power trade off - if you find power sinking - dropping - STOP - recheck the mA draw, these are VERY temperamental..

Something doesn't look right in that photo - you should have another set of headers - one for each Variable - the headers closest to the variables by their respective FET's - Your first one is pre-driver (#1) - Driver (#2) and finally the #3 finals.
Gotcha. I was going to set them for voltage at the gate. When I get to the bench tomorrow I'll take a better look at the amp section but I think there were only 2 headers.

Thanks Andy!!
 
Hmm...Yeah, a lot of people do try this approach, but also remember - that header jumper can be your biggest "Fail Safe" fuse link you have to keep a radio on your table from erupting into flames.

The mA draw is really the only option - for if you try to "balance out" that voltage - you can't - you're at the mercy of the divider - best to let the mA Knee-Rise be the tell-tale sign you're in the ballpark.

I can tell you this, they are working on a concept that - using PIO (programmable I/O) they can "feed" Gates individually thru the "processor" by Mode selection - They' know of the AB2 for SSB and the "latchup" but they are working on methods to change the biasing from Class C in AM and FM to AB in SSB - thru these PIO's. You'll see them soon. They use a buffer chip like the 4066 in a Sound Tracker for the routing and switching. Since they don't use a lot of current this is the ideal method of controlling the Class of Operation using the Mode and the method of Bias is automatic.
 
Hmm...Yeah, a lot of people do try this approach, but also remember - that header jumper can be your biggest "Fail Safe" fuse link you have to keep a radio on your table from erupting into flames.

The mA draw is really the only option - for if you try to "balance out" that voltage - you can't - you're at the mercy of the divider - best to let the mA Knee-Rise be the tell-tale sign you're in the ballpark.

I can tell you this, they are working on a concept that - using PIO (programmable I/O) they can "feed" Gates individually thru the "processor" by Mode selection - They' know of the AB2 for SSB and the "latchup" but they are working on methods to change the biasing from Class C in AM and FM to AB in SSB - thru these PIO's. You'll see them soon. They use a buffer chip like the 4066 in a Sound Tracker for the routing and switching. Since they don't use a lot of current this is the ideal method of controlling the Class of Operation using the Mode and the method of Bias is automatic.
Andy,
Good call on the "pic seems wrong"!!! I looked at the radio and realized the angle did not catch everything. There are 2 jumpers in this radio. I did follow the trace layout and found that the following:

upload_2020-7-29_19-9-24.png

upload_2020-7-29_19-9-42.png


By removing the jumper I am assuming that I can adjust the pre-driver and driver for ma's but what is your thought about a measurement for adjusting the finals? Voltage at the gate?

Thanks my friend!!!
 
Well, I've seen a guy toast one of these - so you have two options. The third may get it out the door sooner with pretty pictures, but it will be back and the customer is going to question why they're back so soon...

One method is safer than the other but again - requires you to own a 5 digit display DVM meter or an Analog one capable of handling 2A or 20A and knowing how to offset the decimal. You can do it with a 4 digit display but remember your multiplier or divisor in tenths.

You can try the voltage - but I know a guy that toasted one by shorting the Gate to Drain on one - so again, this is why I recommend the Ammeter approach.

You have a Scope? Great but that is only going to let you see "best waveform" which may mean too much current and it'll be back in the shop soon enough. (see above)

So this is what I do - it's a little complicated.

Read this thru - then practice...

Put Ammeter in line with power cord set it to 20A for now to handle inrush...

Remove those two jumpers...
Put dummy load in line - 10W best...

Now, - turn on power - Set it to SSB mode USB or LSB don't matter - just don't whistle into the mic ok?

Then let it sit for a minute or two - leave Ammeter on 20A setting - key up radio - observe draw...below 2A? good ...

Un key - you'll need to read this first to understand my method...

REMOVE POWER if you didn't know this and follow thru to properly set "gate" reset voltage - once you know this it's easier...because now you know where to set the pot to turn off the Gates on KEY UP so it won't latch on you...

Most usually just turn the darn thing down to full stop and replace the parts and repower the radio - on AM side and turn up power BIAS until it meets the OEM wattage it once had and be done ...

But that will put the radio back on the operating table too...

You'll need to know which direction you turn the pot to shut down the feed - in my experience it was Counter Clockwise (CCW) - verify - lift FINALS gates (Unsolder them - leave jumpers out disconnected) - TX radio and observe voltage on the Gate lead if it drops below 2 volts or so in one direction - bring it up (CW) to about 2.0Volts...

If you know that 1,000mA is 1A, then 100mA is 1/10th of an amp - 10mA is 1/100th with 1mA being the 1/1000th setting - so knowing where your decimal is, lets you do this on the 2A setting...

You need to pay attention to the 2nd digit behind the decimal - that's your "55" reference

So if 55mA to the ones place - is 0.055 Amps

Ok, SET DVM to 20A - key up - radio, no audio - starting at 20A if reading settles below 2A and radio ok, then set to 2A - note Ammeter - you're going to take that number with your Gate Reset - and add 55 - so if it shows 1.266 = then just add 55 to it - 1.332 or 1.333... this is why I told you to remove the jumpers so the latching and any leakage won't skew your results.

Adjust your Final pot to meet that number...

That's it.
Turn off power...
Reset the jumpers into their seats
Take off the dummy load...

(this goes a lot faster once you have the knack for it and these pass along to your bench for QA - it's easy enough to set up your bench this way and let the radio "idle" in TX mode while you reset the mA reading on the DVM...you can do this on an Analog but scaling may put you at risk for overdone...and always, due to variances in both BRAND of MOSFET, Kind - 13N10 or IRF520 or ERF2030 and LOT number (Batch) )

If you cannot get radio below 2A - then you have other problems but if no choice (to push a repair) use the 20A setting - you'll have to accept "5" as the add number - your last digit on a typical DVM in 20 Amp setting is in the 1/100th - I find this helpful if you find yourself with a radio that has the need to draw more than 2 amps in TX when setting bias on parts that have no jumper to remove.

Why does this work? It's a lot like water pressure - when you turn on a valve you change the pressure in the line because a flow is occurring - voltage stays - but current will rise (your flow) - same can be for the Finals. Only that you're checking further upstream...so you have to be careful with your inrush current on an Ammeter - the DVM's with the 20 amp shunt can easily handle it - once the keyup stabilizes - the lowest SAFE Ampere setting (usually the 2A setting) on the DVM can provide the best accuracy - you then set your draw to it...
 
Well, I've seen a guy toast one of these - so you have two options. The third may get it out the door sooner with pretty pictures, but it will be back and the customer is going to question why they're back so soon...

One method is safer than the other but again - requires you to own a 5 digit display DVM meter or an Analog one capable of handling 2A or 20A and knowing how to offset the decimal. You can do it with a 4 digit display but remember your multiplier or divisor in tenths.

You can try the voltage - but I know a guy that toasted one by shorting the Gate to Drain on one - so again, this is why I recommend the Ammeter approach.

You have a Scope? Great but that is only going to let you see "best waveform" which may mean too much current and it'll be back in the shop soon enough. (see above)

So this is what I do - it's a little complicated.

Read this thru - then practice...

Put Ammeter in line with power cord set it to 20A for now to handle inrush...

Remove those two jumpers...
Put dummy load in line - 10W best...

Now, - turn on power - Set it to SSB mode USB or LSB don't matter - just don't whistle into the mic ok?

Then let it sit for a minute or two - leave Ammeter on 20A setting - key up radio - observe draw...below 2A? good ...

Un key - you'll need to read this first to understand my method...

REMOVE POWER if you didn't know this and follow thru to properly set "gate" reset voltage - once you know this it's easier...because now you know where to set the pot to turn off the Gates on KEY UP so it won't latch on you...

Most usually just turn the darn thing down to full stop and replace the parts and repower the radio - on AM side and turn up power BIAS until it meets the OEM wattage it once had and be done ...

But that will put the radio back on the operating table too...

You'll need to know which direction you turn the pot to shut down the feed - in my experience it was Counter Clockwise (CCW) - verify - lift FINALS gates (Unsolder them - leave jumpers out disconnected) - TX radio and observe voltage on the Gate lead if it drops below 2 volts or so in one direction - bring it up (CW) to about 2.0Volts...

If you know that 1,000mA is 1A, then 100mA is 1/10th of an amp - 10mA is 1/100th with 1mA being the 1/1000th setting - so knowing where your decimal is, lets you do this on the 2A setting...

You need to pay attention to the 2nd digit behind the decimal - that's your "55" reference

So if 55mA to the ones place - is 0.055 Amps

Ok, SET DVM to 20A - key up - radio, no audio - starting at 20A if reading settles below 2A and radio ok, then set to 2A - note Ammeter - you're going to take that number with your Gate Reset - and add 55 - so if it shows 1.266 = then just add 55 to it - 1.332 or 1.333... this is why I told you to remove the jumpers so the latching and any leakage won't skew your results.

Adjust your Final pot to meet that number...

That's it.
Turn off power...
Reset the jumpers into their seats
Take off the dummy load...

(this goes a lot faster once you have the knack for it and these pass along to your bench for QA - it's easy enough to set up your bench this way and let the radio "idle" in TX mode while you reset the mA reading on the DVM...you can do this on an Analog but scaling may put you at risk for overdone...and always, due to variances in both BRAND of MOSFET, Kind - 13N10 or IRF520 or ERF2030 and LOT number (Batch) )

If you cannot get radio below 2A - then you have other problems but if no choice (to push a repair) use the 20A setting - you'll have to accept "5" as the add number - your last digit on a typical DVM in 20 Amp setting is in the 1/100th - I find this helpful if you find yourself with a radio that has the need to draw more than 2 amps in TX when setting bias on parts that have no jumper to remove.

Why does this work? It's a lot like water pressure - when you turn on a valve you change the pressure in the line because a flow is occurring - voltage stays - but current will rise (your flow) - same can be for the Finals. Only that you're checking further upstream...so you have to be careful with your inrush current on an Ammeter - the DVM's with the 20 amp shunt can easily handle it - once the keyup stabilizes - the lowest SAFE Ampere setting (usually the 2A setting) on the DVM can provide the best accuracy - you then set your draw to it...

1st of all, thanks so much for your expertise, time and detailed answer!!!! Now, I got most of this but I have a few questions to be sure that I get this clearly.

[You'll need to know which direction you turn the pot to shut down the feed - in my experience it was Counter Clockwise (CCW) - verify - lift FINALS gates (Unsolder them - leave jumpers out disconnected) - TX radio and observe voltage on the Gate lead if it drops below 2 volts or so in one direction - bring it up (CW) to about 2.0Volts...] I am adjusting the finals pot only for this, right?


[Adjust your Final pot to meet that number...] Where am I measuring this final step? I am assuming that I have the meter between the gate lead and the board so I am measuring the current specifically on the finals gate.

Also, when do I measure and adjust the pre-driver and the driver (through the removed jumpers as you instructed before?

Outside of just getting this right here is my stress. This radio is from a user in Alaska. Yep, Alaska. I'm in Maryland. The user of the RCI 2970 N4 I repaired last month put him in touch with me. I urged the user to just buy a new one and he was set on getting it fixed so here it is. The user lives in one of those areas that you need to fly into. I just want it to be right for him as a return trip is not amazing. I'm praying for a great result!!!!


Thanks again Andy for your kind responses!!!
 
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Ah, sorry, writing an essay for the College Finals Exam and the Tutor that's supposed to proof read, goes on vacation...SIGH.. I putting my life story here, so thank you for being kind too!

Yes, for the Finals - since I've been away from a Bench and knowing the Anytone has seen several revisions. I don't want to make an unexpected left turn - when we should have gone straight... I get ahead of myself I'm trying to condense a "Cliff-notes" manual into one post - not easy...

The radio will still consume the same amount of power (as you adjust) in SSB mode, you can even verify this on another radio for testing your faith in this method. All you are doing is changing the location of the Ammeter to the main power feed. Since it uses full rail in SSB mode, this is the 2nd best way and what many of my techs at the shop did for the work they performed. Set up a bench, one voltmeter - one ammeter and used both for their main go-to - so I'm just passing that along to you.

Disconnecting the jumpers is the safest way to go, then all you have is a roughly 300mW transmitter sitting idle - won't take more than 2 amps, more lucky to take 1 amp.

Disconnected jumpers turn off a lot of the TX section of the radio - so as long as you can keep the meter from blowing it's internal; fuse by setting it to the 20A setting for the TX then once Keyed and all parts are now stable in TX mode, you can safely switch to 2A setting and adjust the mA adding 55 to the displayed number (If your meter has mA great, but be careful, you are on a mail power feed rail - it can blow that meters' fuse.

Ok, Back to those Finals...I wanted you to reset the pot, but in some radios Anytone or otherwise, the Pot may not have a "stop" - this usually indicated the owner has had work done to it. (Bearcat 980 is prone to this) I mean, The pot can rotate freely, adding to your reset problems - and is how many of these radios wind up in the shop - the owners over torqued the pots and now they spin. They can still work, just not reliable for knowing your "ground zero" starting point.

You only check the Gates if you don't know if you have found your "ground Zero" starting point on the pot - if the pot spins - you have lost the main reference - you'll have to find a point in it's rotation to start over. The pot itself should let you pre-set the Gate voltage to 2 volts ...
(or lower than 3 - find it's low spot and note the rotation so you don't "over" turn it to suddenly feed it 6 volts turning it on)​
- just remember which direction you have to turn the pot to turn it DOWN to get to 2 volts, and the direction to turn it up. For if you don't, you can overvolt the gate, latching the Final and kill the final quicker than you can locate "ground zero" to turn it off and start over.

If the pot stops, then usually CCW is the low position - you turn up (Clockwise) from there and watch the Ammeter rise - slowly...easy... 22mA up to 30mA ok...to "boing" "55 to 75" - then you found that brands particular "latch on" point.

Trying to set the voltage or using the scope methods may work to a degree, but when it in Alaska, you may have raw ore to work with in that Tundra, but the Tech to do the work is several Area Codes away...

The mA reading takes precedence (JMO) because of it's accuracy is better, verifiable and presently the best way to set that gate threshold for every MOSFET I've come across - is like an individual - each one has a unique fingerprint of operation - even in the same batch.
 
Second part...
[Adjust your Final pot to meet that number...] Where am I measuring this final step? I am assuming that I have the meter between the gate lead and the board so I am measuring the current specifically on the finals gate.

No, you can but you run the risk of blowing the Gates...and losing the patient - just reset the pots to their lowest voltage setting Keep the Gate lead unsoldered and off the pad to verify you won't have them turn on (Latch) when you power up...to initially check and reset them. THEN resolder the Gates onto their pads...

It's in just knowing the pot position and which way to rotate IF THE POT DOES NOT stop when fully turned up or down - Down is CCW - up is CW for gate voltage. (It Should Be) This is why I asked if you can verify for they do revise the board and they've change the pots orientation and location as revisions go - so they may also change the pots locations for power, variable and ground - which changes the direction of rotation you use to adjust BIAS

Also, when do I measure and adjust the pre-driver and the driver (through the removed jumpers as you instructed before?

THEN... place Ammeter into DRIVERs' Header position - Positive side towards front of radio Negative lead to rear panel side - of the jumper - adjust for 30mA in TX mode (along with Dummy load and no audio) Replace Jumper onto Header - the same for the Pre-driver. So you adjust draw and reconnect jumpers to their respective headers from the back towards the front TX side of the radio.

Verify the radio works - don't try to tweak the BIAS pots, else you may wind up latching them up again and losing the patient...adjust the other AM PWR Hi and LO - check FM mode - SSB modes stuff like that.

Here's' a potential scenario for you when it comes to knowing why you do the back to front.
Keep the Jumpers out until you know you've got your ducks in a row...

IF you are fixing a radio with a Blown Final - Owner says he was using it on SSB and it quit...

You can fix the Final - but what caused the failure - SWR - Voltage - Playing around?

Ever have to deal with Carrier Balance? I've had radios come in with pots turned everywhere but where they should be - because the owner thought they could fix it better than the factory - I came into the picture because the owner gave up and needs help...

Dangerous...

But if they goofed up a setting- you can run the risk of the radio failing again on you and on your dollar for not remembering to keep the radio from going into full power transmit without verifying all the other aspects and the tune-up you will have to perform and the realignments - so whether it's a RCI 2950 or a Galaxy 88 or even a simple PC-122 - pull the jumpers (Mirror Boards) until you have the radio under control - it can prevent what you have left in working parts on that radio from meeting their maker like the rest of it did...
 
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Well, its done....
Thanks again Andy for your time and details!!!!

Now, here is how it played out:
After reading through all of Andy's details I realized that I needed a drink to stop the shaking before I begin.... Just kidding about that one..
- Before I did anything I tested the voltage at the gates of the 4 FET's as a reference. The pre-driver and driver were 3.803 and 3.806 respectively. The finals were 3.687.
- I then powered it off, removed the 2 jumpers and tested the current load on the radio during transmit. It was .912 ma.
- I powered down the radio and unsoldered the gate leads from the 2 finals. I connected a second meter to measure the voltage at the gate leads.
- I powered the radio back on and transmitted the radio in USB mode. Here is one challenge. I did not get any reading. I then checked the voltage at the pad where the gate lead would connect and I did have voltage. It was reading around 3.6.
- I adjusted the VR for the finals bias and found that when I turned it CCW the voltage rose and CW the voltage dropped. Also, the VR's did not have a stop built into them meaning that they would turn 360 degrees. I found that the lowest I could get the voltage for the finals was 2.723.
- I powered off the radio and re-soldered the gate leads back on (as well as the shield).
- I powered on the radio and checked the current draw during transmit. It was .347 ma. I added .55 to that and my target reading should be .897 after adjustment. I adjusted the bias pot for the finals to a reading of .900 ma.
- I turned off the radio and installed the 2 jumpers.
- I turned back on the radio and did a final voltage test at the final FET's gate and they read 3.597vdc.

I am guessing that the bias is set. I did read somewhere that the FET's should have 3.8vdc at the drivers and 3.6VDC at the finals. It seems that Andy's process proves that out unless I missed something (which is very possible). I also re-aligned the power VR's so as to be sure that it does not operate too close to it's maximum power.

I did call the owner (west coast Alaska) to tell him the good news and I asked him about his setup. He admitted that he run's an amp but generally operates the radio at a lower power setting. When we discussed the setup he said that the jumper from the radio to the amp was not in great shape. That may be why the FET's failed. Some bad swr's. He is ordering a new quality jumper.

Now on to my next question. The radio is transmitting about 75hz low on AM and SSB. I need some frequency alignment instructions. Anyone have some?

Thanks as always Andy and everyone who participates!! This is quite the hobby!!!!

All the best!!
 
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Whew, I know that one thing not many do is take the time to do the procedure - so for now we have some verifiable notes...

Pots' - to turn up BIAS Voltage - CCW, to lower BIAS - CW - ok good...

You did it right, you just have to remember you're further upstream than what many are used to...

You will fight the power choke - and the capacitance...

So there is a "lag time" but you did it right. I wouldn't go past 3.6 volts - and that is due to the nature of the finals.

You may not see this easily but - well, another story - I've found Bias voltage can "disappear" from Gates' for several moments while the radio is keyed up and operating - strange to see this but it happens on SSB.

There is an effect like "washing" that the Gate seems to do, it literally "absorbs" that BIAS power for tiny moments - odd to see drops - because usually Bi-polars are just the opposite - their BIAS voltage rises for several seconds at a time until the Bias Diode pulls off that power mixing in with the Signal.

But this can have an affect on your "ticking" the Gates to just turn on. Again, you can scope the outputs and think you're ok - but you just did something that makes every MOSFET radio different from another - each change in the design makes one way easier over another - but not foolproof. Gate voltage aside, the BIAS current changes here too - sounds odd to say that but remember - as the device turns on, the field encounters an EMF effect that bounces back at it's efforts to load up the BIAS onto the Gate - so as the part turns on, is scavenges the Gates signal to do just that, turn on.

IF your Gate is using a high-impedance feed - this shows up quite often and makes people OVERVOLT the Bias without taking the time to see the stabilization that occurs afterwards. When people listen on SSB, some people hear the "Fuzz" and "Choppy" effects from the under biasing like you would hear from Bipolar radios or Class C amps on SSB - but once enough drive hits the Gate - BIAS problems are moot - you're fine. Tweaking is harder on single - sided BIAS networks, where there is only one pot and it's ACROSS the Gates' TX 8V feed.

Now are you're finding out - trimming back that Gate voltage and it only dropped to 2.7 - gives you a clue as to their trimmer range, it's not much.

They realize the issue around the "lag time" that the Bias' ability to disappear at times of low-drive signal. So your Bias didn't drop to the floor, but operated in a window I have discussed about before.

https://www.worldwidedx.com/threads...8-and-mb8719-boards.95853/page-11#post-707916

You can read all this at the above link at your leisure - WOOF - it's long but may help you deciper how they did that 6666's biasing scheme - if not, well they are working towards "constant current regulation" methods to push the voltage back onto the gates...

Again if you go too far, you can over-volt the Gate and it may take too long to remove the power (That High-impedance feeder line) that can make it latch on too long and eventually fail. Too short they get choppy, but many think the voltage should be set, and only voltage will do - period.

Not so.

That Gate's Turn-On BIAS threashold "wiggles" when driven by low-level signals - it can scavenge the signal as part of the Drive needed to turn on the Gate and use everything the Gate has got to do so. They're just good switches.
 

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