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Hello, in my FT-980:? when rotating vfo knop, in the display numbers are changin by 10 hz,thats ok, but the real frequency is not changin until one khz is reached. So, by one khz steps. I have replaced some parts in vfo board, no success.
I appreciate, if someone can give me advice, where to start , "march order".
73's Aimo, oh6nes

Hi Aimo,

Nothing comes to mind (LDB shouldn't cause this for example). I haven't seen this on my rig ...

Q: Are there any other LEDs lit except
? ? ?1. VFO (above the display)
? ? ?2. Ham (above the Ham button)

--
-Mat Breton, N8TW

Tnx for reply.

No others, only those two.
Btw. I have Ft-980 Technical Supplement and I have measured values on the vco/pll and vfo units. BUT.
Don't know where to start. In how many places the frequence is regulated and expecially those hz/ 10 hz steps.
What to check and in what order.
Changin components, etc.
73
Aimo, OH6NES

OK, I have an idea. But first a few basics:

1. The VFO frequency is driven by a microcontroller controlled PLL into the 1st mixer. The scheme is pretty complex and is shown on page 49 of the tech supplement.?
2. The Microcontroller controls this PLL via a 21-bit wide digital bus.

We don't know if the problem is in the PLL or the microcontroller (or the connectors/wiring between), so let's first divide the problem in two.

Using a multimeter, check the VFO board connectos P07 and P08. P07-Pin 1 is the LSB, and P08-Pin13 is the MSB. As you spin the VFO dial, you should see the lower level pins toggle back and forth in BCD-like fashion (pin 1 toggles every 10 hz, pin 2 toggles every 20hz, pin 3 toggles every 40 hz, and so on).

Give this a try and let us know if the uC signals are getting from the CPU board to the VFO board!!!

--
-Mat Breton, N8TW

Measuring the voltage changes when spin the VFO dial, steps?

Very good, we are making progress I think. It appears that the CPU commands are not reaching the VFO PLL. Since the CPU separately drives the VFD display, this would explain all the symptoms you are seeing. We have a good idea of what the problem is ... we just need to locate where the problem is :)

Note: I say "appear" because there is a small possibility the decoder/counter IC on the VFO board is fried and holding the lines up/down. More on that below ...

Next is to check the interconnects: the FT-980 VFO PCB (like most of Yeasu's PCBs in that era) is a single-sided design. These types of boards have known long-term reliability issues with solder joints due to the uneven flexing that occurs as they heat & cool. Additionally, the boards are neither temperature-stabilized nor fibre-reinforced, which exacerbates the issue.

Going to the CPU board, can you check the equivalent pins on that side (J6003 & J6013 I believe):

Outcome 1: If you see the correct signals there, we know we have an interconnect problem.
Outcome 2: If you don't see the signals, we need to eliminate the possibility of a fried VFO IC: disconnect the bus between the boards and retest. I

Outcome 2A: f we have a bad VFO IC the signals should "magically" start working.
Outcome 2B: If they do not, it would appear to point point to a CPU board issue. We'll cross that bridge if it comes to that.

Give these next set of tests a try and we should hopefully figure out where the issue is!

--
-Mat Breton, N8TWn

All,

If I was a betting man (and I've been known to wager a bit here and there) I'd place money on the problem being with Q27, a uPD8255AC-5 programmable I/O controller. This takes muxed CPU data and drives a number of subassemblies in the rig, among them the VFO and PLL.

One of these ICs went bad in an FT-980 and caused the tuning to simply not work (among other problems). Replacing it fixed the issue. Yaesu must have foreseen potential troubles in this portion of the CPU Unit, as Q25-Q27 are socketed.

73 - Fred, N8YX

When I get time I'll dig into the schematics again. We are missing something I think ...


--
-Mat Breton, N8TW

Ok.

Hello, I have the same problem, on the vfo I can see how I go up and down in frequency, but the real change is every khz, I have measured the impulses in (P07 FROM PIN 1 TO PIN8) with an oscilloscope, and I can see the pulses, increasingly wider as I go up the pin to pin 8 (P06

Hello, I have the same problem, on the vfo I can see how I go up and down in frequency, but the real change is every khz, I have measured the impulses in (P07 FROM PIN 1 TO PIN8) with an oscilloscope, and I can see the impulses, increasingly wider as I go up from pin to pin 8 (P06 FROM PIN 9 TO PIN 17) on pin 17 I can still see from time to time how the impulse rises. Luckily I have 2 vfo boards, but both have the same symptom, it is difficult to have the same failure on 2 different boards. any ideas?

Hello All,?
Hello Electronica valvulas ! First, you will not get more help by repeating your messages? and please sing with a name or callsing : we are humans !
I have a FT-980 saved from scrap but the problems were more on analog side...
The VFO unit of the FT-890 is digital, and controlled by CPU unit. The dial unit give only pulses to CPU unit.
The display take the data from the CPU unit. This can be observed on block diagram of page 59-62.
The VFO is only controlled by the CPU board

If the dial change only the 1 kHz steps, it will be more a problem on the CPU unit.
Do the following steps :?
- remove the battery to reset the CPU RAM.
- Select only HAM VFO , only its own LED is lighting and all other must be off !
- Enter a frequency using key board : type "ENT" 07000.00 "ENT"
- Check the real frequency ? Do you receive on 7.000.00 or is it shifted ??
- Depends on the result try +100 Hz up by typing 7.000.10 "ENT" . Does shift the Rx frequency ?
- If yes,it is more a display problem !

Based on a constructive and detailed response I can support you for next steps...

73 de F5RCT JMat (Jean-Matthieu), France, Strasbourg north

Hello, thanks for the response, first of all I'm sorry, I wrote the message several times because it was not published, then I realized that an administrator had to authorize it. As for the ft980, I did what he told me, the ft980 injected a signal at 7000khz, the vfo reads 7200khz, and the jumps are 1khz.