MR80 display ranging

[Gregory]

The digital display on the MR80 has become unstable

Turn the unit on, and maybe 1/2 to 1 hour later, the digital display is ranging "all over the place" and fast! I cannot tell if it's counting up, or just going erratic. There is no change to the station or the Signal Level displayed. One symptom that gives away the condition is.. the tiny relay that controls the `1´ hundred digit goes "tink, tink, tink" as the `1´ character is lit/unlit. This sound (of the relay) can be heard within 8-10 feet or so. The periodic nature of the relay sound leads one to belief that its ranging in one direction.. not just at random.

The tuner is working ok.. but the display has become intermittent. I've had PM discussion with some of the leading Techs in here, but those kinds of threads often fizzle out.

Yes, have been in there to disconnect-deox'd-reconnect many of the internal plugs, including the RCA cable. Where to start looking?


-Greg

 

[dewickt]

Check the power supply board, cap may be going bad putting humm on the 5V and upsetting the level converter in the counter module.

 

[Rich Andrews]

What Terry said!

The good news on the display is that it is all discrete logic.

The bad news on the display is that it is all discrete logic.

Separate counter IC's, gates, etc. makes the parts cheap and plentiful. Getting in there to replace them is another matter. If it were my unit, I would start by ordering a complete complement of ICs, machined pin sockets, caps, and regulators. Should cost about $50.

Since it seems to be heat related, some freeze spray should help narrow things down - likely to the temperature sensitive/defective part.

 

[clinic-audio]

Hello Gregory

Your trouble is coming from the power supply as Terry say but I will give you a little more details :
Change all the Roderstein capacitors on this board and you will see your trouble disapear ....:thmbsp:

 

[kevzep]

Awesome information guys, I am watching with interest and making notes as I have an MR80 on the way, although it has been to Terry, so it should be good for enough years that I would have forgotten about this thread if and when this fault may or may not develop.....

 

[clinic-audio]

Hello Kevzep

All the MR80 has this problem after a certain lap of time .....
I would suggest you (if you make a complete check up of your tuner to delete the 6 "silver " springs to replace them by an upgraded version ( gold plated ) to avoid for ever any troubles with the 4 preset touch control and 2 scan up and down control
See my pictures :thmbsp:

 

[Gregory]

Hello Gregory, Your trouble is coming from the power supply as Terry say but I will give you a little more details: Change all the Roderstein capacitors on this board and you will see your trouble disappear.

Great advice, thanks!!

From Terry that is... and caps are relatively easy to replace. The touch sensitive buttons have been good over the years, but there was always one or two that acted up. Seems to be relative to humidity? For now I'd very much like to get the display settled down. Leaving the room while the [ 1 ] hundred MHz digit is blinking every 1-1/2 seconds, and relay`tinking´ away would beat on it too much.. me thinks! :nono:


-Gregory

 

[clinic-audio]

Hello Gregory

I just wanted to tell you : take a great care for the position of the both small connectors and the bottom left of my first picture (power supply )
If you mix them and connect the wrong one , you will damage your frequency counter so be carefull ! :thmbsp:

 

[kevzep]

Hello Kevzep

All the MR80 has this problem after a certain lap of time .....
I would suggest you (if you make a complete check up of your tuner to delete the 6 "silver " springs to replace them by an upgraded version ( gold plated ) to avoid for ever any troubles with the 4 preset touch control and 2 scan up and down control
See my pictures :thmbsp:

Thank you for the information, I will be checking this on mine when it turns up.....

 

[MX117.MC7150]

clinic-audio:
Where do you purchase the gold-plated springs?

 

[Gregory]

take a great care for the position of the both small connectors and the bottom left of my first picture of power supply. If you mix them and connect the wrong one , you will damage your frequency counter so be careful !

Thank you again.. you're photos are very good.


-Gregory

 

[c_dk]

Since the touch pads were used by Amana for their microwaves I would guess a appliance repair parts source.

 

[clinic-audio]

They are made for me ..

Gold plated 24K (!)

I already did this change in 9 MR80 and none with the preset touch give any malfunction anymore

 

[Gregory]

Hello Kevzep, All the MR80 has this problem after a certain lap of time.... I would suggest you delete the 6 "silver " springs to replace them by an upgraded gold version.

Thank you for the information, I will be checking this on mine when it turns up.....

Proven Performance

To demonstrate the performance of this tuner, and for the new guys from France and Australia—the MR 80 was set up in Arlington Heights, Illinois (a suburb of Chicago) with a Channel Master 4408 FM Stereo Probe antenna mounted on a rotator.

The goal of the exercise was.."to see if a station could be tuned at each of the 100 possible `slots´ on the FM band."


Chicago FM Log (1988)




Baltimore FM Log (1991)





Chicago antenna photos – Single 4408 Yagi

Installed: 11-25-88, Removed: 12-29-89


Front of house


Back of house


Baltimore antenna photos – Stacked 4408 Yagis


Front of house


Back of house


Antenna Carton




Attached are Chicago and Baltimore FM Log spreadsheets.


The digital display issue won't take away from the Superb DXing and low distortion capabilities of this tuner.


-Greg

 

[kevzep]

To demonstrate the proven performance of this tuner, and for the new guys from France and Australia.. the MR 80 was set up in Arlington Heights, Illinois (a suburb of Chicago) with a Channel Master 4408 FM Stereo Probe antenna mounted on a rotator. The goal of the following exercise was "to see if a station could be tuned at each of the 100 possible `slots´ on the FM band."

FM Log > > MR80 - Chicago FM Log​

Now I see the HTML file must be update to include a link to the Antenna photos.

Channel Master 4408G Chicago

Channel Master 4408G II


So we won't let a digital display issue take away from the Superb DX and low distortion capabilities of this tuner.


-Gregory

Thank you Gregory, thats very interesting......

I am in the line of sight to the transmitter of the station I listen to, in fact all the stations are on the same building in the city about 12 miles away......but we have a lot of stations and certainly one of them near the one I listen to over-modulates....
So the MR80 is going to be a welcome addition......

Meanwhile back to the thread topic......

 

[MX117.MC7150]

They are made for me ..

Gold plated 24K (!)

I already did this change in 9 MR80 and none with the preset touch give any malfunction anymore

Be a whole bunch easier to ship a set of springs to the U.S. then an MR80 to and from France. How much would you want for a set?

 

[clinic-audio]

Hello MX117.MC7150

The best way and the less expensive one, would be to ship me a set (6 original springs bought from the factory , I say bought because they need to be new for GOLD treatment ) .
Send me a MP
Thank you !

 

[Gregory]

Thanks for that advise again

At the rate things happen around here... I'm just getting a good look at the MR 80 schematic, SHEET 2 of 2 and identified at least 10 power supply caps that could be replaced. There are six or seven on the schematic for PC board designated < 11 > PARTIAL. It will be a no-brainer to replace those caps.

There's an error or two on the schematic. The 32.5 VAC lines through board < 11 > near the power transformer are mislabeled, or the INTERCONNECTION DIAGRAM is mislabeled. Not a problem really.


Downstream PS caps

The question is.. would now be a good time to replace the other downstream power supply caps on the MAIN PCB? assuming they could be accessed without major dismantling of the tuner?


-Greg

 

[Gregory]

MR80 with covers off

It's slow enough today to be able to open the MR 80 and check access to these caps. They're located in the front right corner of the unit, seen to the left.. upside down on the bench in the photo below. You can see two shielded cables running across the underside of the tuner.. from the Output section to the VOLUME control.




Aft PC board

One can quickly see other caps that need to be changed (see arrow). Here's a view of Power Supply board in back, where the AUDIO OUT jacks are located. There are two 10uF Non Polarized caps, C801, 805 (see arrow). The FIXED outputs have no NP caps inline. The shielded cables are in lower right




Might as well replace all of these caps while at it.


-Gregory

 

[kevzep]

Nice meticulous thinking and work going on as usual Gregory, I am watching with interest.
I like your photography too......

Excellent work....