TK880 vs TK880H

[Flameout]

Are the only differences (besides the obvious larger heat sink of the 880H) on these two radios just the RF MOSFET Amplifier Module and the extra voltage regulator on the 880?  Am I missing something else?

I bought a non working 880H and was able to get it to power on by replacing a diode, a capacitor and the one voltage regulator, but there is no audio and no power coming from the antenna, even though it is transmitting and receiving.  I started looking at the two and those are the only differences that I see. Seems weird that the lower power 880 has the 2 voltage regulators where the 880H just has the one. Also, any idea why the 880 has no audio and no power coming from the antenna wire (I tried external speaker and had swr?watt meter attached to antenna wire with zero SWR and zero watt output - even though when I transmit, it is being picked up on an ht nearby) Another thing too, even though the display works on the 880H, the LED's don't

Also, don't mind those extra wires. I was testing these radios as RX radios in a portable repeater

[axorlov]

3 hours ago, Flameout said:

watt meter attached to antenna wire with zero SWR and zero watt output - even though when I transmit, it is being picked up on an ht nearby

You have dummy load or proper antenna on the other side of your power meter, right? Right?? If yes, that is a very strong hint that power amplifier is a toast. I'd say 99% probability. The HT nearby receives the very low radiation from the internal low-power traces and wires.

[Flameout]

40 minutes ago, axorlov said:

You have dummy load or proper antenna on the other side of your power meter, right? Right?? If yes, that is a very strong hint that power amplifier is a toast. I'd say 99% probability. The HT nearby receives the very low radiation from the internal low-power traces and wires.

Oh, I did have an antenna connected. I guess the power amplifier is the part that I have circled in my photos? Looks to be around $40 for the 40w, for the 880H. Not sure if it's worth the gamble. Is there a way to test the power amplifier that you (or anyone) know of? I guess that also affects the audio output?

[Sshannon]

5 minutes ago, Flameout said:

Oh, I did have an antenna connected. I guess the power amplifier is the part that I have circled in my photos? Looks to be around $40 for the 40w, for the 880H. Not sure if it's worth the gamble. Is there a way to test the power amplifier that you (or anyone) know of? I guess that also affects the audio output?

A schematic and an oscilloscope sampling signals along the path to and from the antenna is what you probably need to do.  That’s what I would need to do for a circuit that I was unfamiliar with.

[Flameout]

Ok, thanks. Well that is well above my pay grade lol. I may take the risk and offer this seller $30. I just have no idea what else may be wrong with the radio. It powers up, programs, red light comes on when transmitting and green comes on for receiving and it is working ok as the rx radio in the repeater setup and sending that signal to the tx radio https://www.ebay.com/itm/403511558565?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=6B03kewjR7i&sssrc=2047675&ssuid=0zihXCkJQWG&widget_ver=artemis&media=COPY

[axorlov]

1 hour ago, Flameout said:

I guess the power amplifier is the part that I have circled in my photos?

Yes, this is the part. I agree with Sshannon, oscilloscope would be needed. But here is the datasheet for the PA, just in case: https://www.mitsubishielectric-mesh.com/products/pdf/ra45h4452m.pdf You can quickly check the voltages on pins 2 and 3 (refer to Page 2 in datasheet). Maybe the PA is fine, but there is no driving voltage. It also may have an effect on the audio amplifier.

[Flameout]

49 minutes ago, axorlov said:

Yes, this is the part. I agree with Sshannon, oscilloscope would be needed. But here is the datasheet for the PA, just in case: https://www.mitsubishielectric-mesh.com/products/pdf/ra45h4452m.pdf You can quickly check the voltages on pins 2 and 3 (refer to Page 2 in datasheet). Maybe the PA is fine, but there is no driving voltage. It also may have an effect on the audio amplifier.

Thanks for the link. I'm getting a nice little collection of Kenwood TK-880 files. 

I checked pin 2 and 3 and only pin 3 was gettting power, so maybe the PA is good after all. If I were to bypass everything and temporally supply the (13.6) voltage to pin 2 to see if the radio would actually transmit, would that do more harm than good? I guess I'll start tracing back and see if I can find the problem

[axorlov]

5 minutes ago, Flameout said:

and temporally supply the (13.6) voltage to pin 2

Careful here. Pin 2 is 6V, Pin 3 is 17V. Refer to the table on Page 2 in the datasheet.

Edit: these are max values, so Pin 2 should be around 5V, and Pin 3 is around 12V.

[Sshannon]

8 minutes ago, Flameout said:

Thanks for the link. I'm getting a nice little collection of Kenwood TK-880 files. 

I checked pin 2 and 3 and only pin 3 was gettting power, so maybe the PA is good after all. If I were to bypass everything and temporally supply the (13.6) voltage to pin 2 to see if the radio would actually transmit, would that do more harm than good? I guess I'll start tracing back and see if I can find the problem

According to the data sheet, Vgg is rated for 6 volts, so I wouldn't do that.

Where does the input to Vgg come from in the circuit?  See if you can find a Service Manual and look at the schematic of the TK-880.

[axorlov]

Btw, the service manual with the schematics for the V2.0 version of the radio is here: http://www.repeater-builder.com/kenwood/pdfs/tk-880h-svc-man.pdf

I'd walk through it it with you, but I'm busy at my day job right now. LOL

[Flameout]

oh wow, ok. I just read through the data sheet again (I may have to read it a few times) I just checked that voltage regulator that I put in. It was showing 13.8v  / gnd / 7.88v so pin 2 of the PA is getting that 7.88 from the volt reg so I guess I can start from there, or should it actually be 6v? I guess the 17v is like the maximum?

At least I can hold off on buying a new PA for now. I know I'm probably putting more into this old radio than it is worth, but it's kind of fun trying to figure it out

[axorlov]

7.88V seems to be high. The second table on page 2 of the datasheet shows the nominal parameters: Vdd=12.5V (that's likely your supply voltage, so no surprise if it is 13.6V), Vgg=5V. P-in=50mW, and since your nearby HT can receive signal, it looks like you are getting this signal in. Still try to visually check the traces on PCB for cracks and bad soldering, use a magnifying glass.

[axorlov]

Ahh, screw the day job, this is fun. Here is the excerpt from the service manual, page 72:

 

Notice the R:0.01V T:7.52V (in pink) close to the bottom-left corner. So, maybe 7.88 is not too high, after all.

[Flameout]

I checked the voltage regulator on another 880 and it was basically the same. 13.8 and 7.94. I'm looking over the board now with strong magnification under a bright light.(I will probably need some Tylenol after this)

I took the board out of the case, so the photo is the part that was hidden by the case. Is that white stuff normal or are those components failing or already failed?

[axorlov]

Nothing looks wrong on this pic.

The voltages seem fine. Without the oscilloscope with 500MHz bandwidth it's hard to diagnose. However, if you put your multimeter (totally not rated for 500MHz) into Voltage-AC mode, and check pin 1 when pressing PTT, and you see <anything>, the signal goes in. Now, do the same test on pin 4, where the amplified signal should be. Keep antenna or dummy load connected.

[Flameout]

I did those tests and nothing at all on pin 1, 2, 3 0r 4 when set to Voltage AC. Went back to DC and did the same test. Keying the mic gives 0 on pin 1, 1.7 on pin 2, pin 3 is the 13.8 so no change there, and pin 4 was 1.5. Of course still Zero watts and zero SWR. I'll keep playing around with it. Maybe I'll get lucky

[axorlov]

Results are inconclusive without the proper testing equipment, however signal is being radiated from somewhere, so it either can't reach the PA, or PA is shot. The supply voltages on PA are correct, you confirmed it. I'd try to test AC voltage when keying mic at the Q7, Q202, Q204, Q205. Oscilloscope would be very handy here.

[Flameout]

I removed the voltage regulator and put in a new one. When I had the old one out,, I realized the board was pretty bad. Looked like part of the of foil on the board was folded over. I cleaned the board best I could, put in a different voltage regulator but no change (the fibers in the photo are probably from the qtip I used to clean)

Meanwhile, I picked up another (very clean and working) TK880H, but this one has an N connector for antenna (did they ever come from Kenwood this way?) A wire with a bnc connector and a factory 15 pin plug.  What would that bnc connector be for? 

[gortex2]

They never came with N connectors but I know alot of guys who swapped them out to N but normally N(F) and not N(M) like yours shown. Look for voltage on the BNC, or Audio. May be a discriminator output for going to a meter. I have some BNC cables for my CDM to go to my service monitor while aligning simulcast. Could have been used for something like that. I guess the other thought is they broke RX and TX to separate lines. Not sure why but seen lots of modified stuff over the years. If it was used as a control station on a TX combiner and RX multicoupler I can see why.

 

[Flameout]

This is were the BNC is connected to on the board. I'll try doing some testing later. 

[axorlov]

Connected to C201-R201-R202-L200 filter. Looks like an input for a secondary receiver, behind the antenna switch. Maybe for scanner working off the same antenna? That would explain BNC connector too.

Clever, I need to remember this for possible future installs.

Edit: the more I look at it, the more I think this is for a scanner working off the same antenna. The tap is behind the antenna switch (to not fry the receiver) and before the L203 band pass filter (to keep wide band receive). Refer to page 28, fig 2 in service manual.

[Flameout]

2 hours ago, axorlov said:

Connected to C201-R201-R202-L200 filter. Looks like an input for a secondary receiver, behind the antenna switch. Maybe for scanner working off the same antenna? That would explain BNC connector too.

Clever, I need to remember this for possible future installs.

Edit: the more I look at it, the more I think this is for a scanner working off the same antenna. The tap is behind the antenna switch (to not fry the receiver) and before the L203 band pass filter (to keep wide band receive). Refer to page 28, fig 2 in service manual.

I couldn't make heads or tail out of that when I tried looking up in the service manual. I was checking it for any voltage and also connected an swr/watt meter with zero results. Makes much more sense now.

I actually picked up two of the 880H radios, and checking the power output, I'm barely getting 20 watts on high power Thought someone might have swapped the 880H boards with 880 boards, but when I opened them, they both had the 45w PA (although completely different from the RA45H4452M in the original 880H I started the thread with). What causes the diminished output. Just old radios? Kind of disappointing to not get the output I was hoping for

 

[axorlov]

I have three TK-880H and all three show 30W on high power, when driving dummy load. Nominal supposed to be 40W. I use Diamond SX-600 power meter, which I trust, however, it was never compared to a better meter. 20W is a bit low. Are these "-1" radios? Congrats on starting collection of TK-880!

[Flameout]

Yeah, I'm up to 6 - 880's now. Well, 5 1/2 would be more accurate. Three of the 880's and 3 - 880H's

I tried testing with two different power meters. One is the MFJ-847 and the other is the SW-33 (I don't see any other name on it) They are both pretty close in their readings, but I think the MFJ is a little more accurate. I have a dummy load, but it gives me worse SWR than the antenna does!

Just on example of my tests. The 880H with that BNC connector gave me 18.1 watts and SWR of 1.38 on 462.650 and the other 880H was same SWR but 25 watts (25 was the max I got out of that radio and the most I got out of the "bnc" radio was 18.2 watts. With the same tests, I get much more power out of a couple of old Icom radios. F2821 and F6011. They are listed at 45 watts and put out around 42

 

[axorlov]

One of the reason of low power is that this TK-880H with BNC tap was realigned for ham band 70cm. Did you happen to save the original codeplug for it to see what was programmed? Check Realignment chapter in the Service Manual, maybe it may help.

Edit: Another thing to check, to close this matter: measure the voltage at the radio, while pressing PTT. If it is still 13.6V your power supply, wires and connectors are good.

[Flameout]

yes, I do have the original codeplugs from all of the radios. Not that I understand that Fleetsync programing though. Saved as a .SDT and a .DAT file. I couldn't find any frequencies in there though, showing what they were programmed at. Voltages all stay consistent when transmitting. I'll read through that Realingment section a few more times. Eventually it might make sense lol

Even though these radios are listed at 450-490 MHz, they can still be programmed in the 420-450 MHz 70 cm bands?