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MR80 display ranging

If I were you I would invest in a scope. You could change every capacitor in it and still not solve on the problem.

Richard - who has the original PS caps in his 1968 C22 and they are still good.
 
Rich Andrews said:
If I were you I would invest in a scope. You could change every capacitor in it and still not solve on the problem.

Richard - who has the original PS caps in his 1968 C22 and they are still good.
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Yes.. have started a thread in DIY and the Tek TBS1000 looks very attractive. Wonder if it can do FFT with 100 dB dynamic range? That way I could revisit the digital and transistor electronics classes from junior college! Does Malvino, Transistor Approximations ring a bell?


-Gregory
 
On pgs. 10-1 and 10-2 of the MR80 Service manual is a Counter Assembly checkout procedure that Patrice of Clinique Electronics has pointed out. {Thanks for that!} So we're moving forward with diagnosis of the tuner. Rich mentioned installing all new ICs for the Counter PCB. Now that would be something I'd look into! Anyone want to delve into the specifics?

First things is to replace another 8 or 10 electrolytic caps.


-Gregory
 
Gregory said:
Yes.. have started a thread in DIY and the Tek TBS1000 looks very attractive.
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But the new Tektronix scopes are disposable scopes. They are not repairable in the sense that the 400 series scopes are. The problem is custom ICs and surface mounted devices. The new scopes are loaded with them and the ICs (or in many cases just replacement boards) can only be sourced through Tektronix. When they drop support in 7 years or so, and they run out of boards that is the end of the scope. Seen it happen all too often. Do some research before you buy.

There is one feature that the 400 series has than few modern scopes have and that is a channel A output. Some very neat setups and amazing scope channel sensitivity can be realized by cascading channels. Imagine having a frequency counter and scope display done with a single scope probe attachment. That sort of setup is handy when troubleshooting mixers in tuners.

You do what you want, but I would not have a new digital Tektronix scope.

The 465 would likely be more than sufficient for your needs.

The link below says this:

"Used digital scopes that have problems are virtually unrepairable." Which means that once support goes away for a new one, it is scrap.

http://reviews.ebay.com/Buying-an-Oscilloscope-on-ebay?ugid=10000000001568756

You have been warned.

Sorry for the rather brash statements but oscilloscopes are something I happen to know something about. I was in the the used test equipment biz for a while.

If you want a hot setup, get a 475 with the DM44 option. The LED display will look cool. Not the most useful option IMO for audio work, but it looks nice. The DM44 is really nice for measuring timing events.


Richard
 
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Rich Andrews said:
But the new Tektronix scopes are disposable scopes. They are not repairable in the sense that the 400 series scopes are. The problem is custom ICs and surface mounted devices. The new scopes are loaded with them and the ICs (or in many cases just replacement boards) can only be sourced through Tektronix. When they drop support in 7 years or so, and they run out of boards that is the end of the scope. Seen it happen all too often. Do some research before you buy.

There is one feature that the 400 series has than few modern scopes have and that is a channel A output. Some very neat setups and amazing scope channel sensitivity can be realized by cascading channels. Imagine having a frequency counter and scope display done with a single scope probe attachment. That sort of setup is handy when troubleshooting mixers in tuners.

You do what you want, but I would not have a new digital Tektronix scope.

The 465 would likely be more than sufficient for your needs.

The link below says this:

"Used digital scopes that have problems are virtually unrepairable." Which means that once support goes away for a new one, it is scrap.

http://reviews.ebay.com/Buying-an-Oscilloscope-on-ebay?ugid=10000000001568756

You have been warned.

Sorry for the rather brash statements but oscilloscopes are something I happen to know something about. I was in the the used test equipment biz for a while.

If you want a hot setup, get a 475 with the DM44 option. The LED display will look cool. Not the most useful option IMO for audio work, but it looks nice. The DM44 is really nice for measuring timing events.


Richard
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Rich is right, NEVER buy a digital scope........They are nothing but trouble, I have a friend who is a audio tech and also does digital logic and eprom reprogramming etc, he has to have a digital scope, but has nothing but trouble with them.....and these are Tek scopes too.....


TEK 465 or 475, there are plenty around, and they are as Rich says fully serviceable, I have seen them selling as restored units too.....a 465 is a nice beast and will do everything you need.....Make sure you get decent probes...

Or if you want to spend a bit more, you could go for a TEK 2445 or 2465.....as I said earlier, I have a 2465, really nice scope too.
 
kevzep said:
R.Make sure you get decent probes...
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Agreed!

Don't mess around with cheap knockoff probes. Get a good 1 meter x1 Tektronix probe and a couple of two meter x10 Tektronix probes. Why 1 meter in a X1 probe? Higher bandwidth than a 2 meter and that extra bit of gain comes in very handy when troubleshooting tuners or measuring residual noise. You may not need it all the time but when you do you will be glad you have it.



Richard
 
Rich Andrews said:
Here is another link. http://www.eevblog.com/forum/projects/tektronix-465-repair-and-restoration/

Even the transistors are socketed!
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I don't know what to do now. A reply in the DIY forum said to buy a new digital scope. OTOH three or four responders recommended a classic Tek. No longer comfortable with auction site, it will have to be Craigslist or something like that. Anyone know a good equipment vendor? I'd not want to restore a scope before using it. What about calibration?


-Gregory
 
Gregory said:
I don't know what to do now. A reply in the DIY forum said to buy a new digital scope. OTOH three or four responders recommended a classic Tek. No longer comfortable with auction site, it will have to be Craigslist or something like that. Anyone know a good equipment vendor? I'd not want to restore a scope before using it. What about calibration?


-Gregory
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I wouldnt even think about restoring a scope, they are pretty complicated beasts, and there are some EXTREMELY high voltages in them (CRT supplies).
Not for a new-comer, and you really have to know about scope functions etc etc....
I cant remember where I saw those TEK scopes, but they were refurbished and even had a guarantee of some kind, I will have a look.

Seriously, you do not want to buy a digital scope. I have got my TEK2465 (analogue/digital memory, 4ch 350mhz) but I still have a TEK 465 which I bought for next to nothing, and its a mint runner....its very reliable and all the functions work as well as the day it was made....
For the work you will be doing the TEK 465 well exceeds what you actually need....
As mentioned make sure you get decent probes...
 
I had the same issue with my MR-80 and it turned out to be a bad IC and multiple bad solder connections and a couple of compromised traces. The guys at Audio Classics got mine running better than new.
 
Gregory said:
I don't know what to do now. A reply in the DIY forum said to buy a new digital scope. OTOH three or four responders recommended a classic Tek. No longer comfortable with auction site, it will have to be Craigslist or something like that. Anyone know a good equipment vendor? I'd not want to restore a scope before using it. What about calibration?


-Gregory
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Calibration? Neither you nor I are doing anything that requires calibration. Either it works or it doesn't. I haven't calibrated my scope in 8 years I have owned it nor do I care if it is out of calibration. It is accurate to within 1% or better and I can still see a 108 MHZ signal coming out of my ST1000A.

A scope can fail at any time so calibration is sort of pointless. All I am concerned about is if it triggers well, is reasonably close to reading what it is supposed to in terms of peak displayed voltage, (mine is right on) and all the functions work. The rest is just minor tweaks and verifying power supply ripple, etc.

The scope CRT has less high voltage than a color TV picture tube by about 1 order of magnitude. Sure it is high, but the danger areas are well marked on the PC boards.

In the case of a failure, I have used the scope to troubleshoot itself. I recently had a cap go bad in the power supply. I used the scope to identify the bad cap in it's own chassis. It was one of those things where it was working fine one day and not the next.

I would have no worries buying a scope from the fellow auctioning off a 465 at the link below. It is calibrated and more importantly, guaranteed.

The only question I would have is if the CRT phosphor was burnt or dim in any one spot at all. If the seller says CRT is good with no burns or fades, then I would trust him.

http://www.ebay.com/itm/Tektronix-4...89819?pt=BI_Oscilloscopes&hash=item48462cd9fb
 
Rich Andrews said:
The scope CRT has less high voltage than a color TV picture tube by about 1 order of magnitude.
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I realize this Richard, it might be fine for guys like us to say this and dismiss it to some degree, all I am doing is pointing it out to someone who pokes around in SS audio gear, 500VDC is going to be frightening to someone who hasnt seen much more than 60VDC in the gear they normally work on....
I feel better warning people and I dont think its a bad thing.......The Tek465 has "thousands" of Volts DC and yes those areas are marked, BUT its still worth the warning.......
You and I know how those voltages like to "jump" out at the nearest fleshy substance passing by......but new guys dont necessarily....

EDIT: I would also totally buy from this vendor too, in fact I think I did nearly buy a scope from this guy before a deal came along which suited me better, it was more risky because there was no guarantee like this one, but I got away with it....
 
For someone that pokes around inside tube gear, the scope crt voltages aren't much higher than what is found in a MC275. Pretty close to what is found in a MI3 or MPI4.

I bought two 465 scopes at roughly the same time. I knew one had a bad CRT (bad shadow mask) but I bought it for spare parts. The other was good but needed to be cleaned. I think I spent about $250 for both. So far I have robbed one cap out of my parts scope. It was well worth the $65 I spent on the known bad scope. The bad scope came with 4 probes so I broke even from the very start.

Neither of my scopes came with a guarantee.

One day I might find a good crt for the other scope and then I will put it into working shape again.

Richard
 
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Trying to get back into "project" mode after being away for a bit and wondering today if, or what ESD precautions should be taken when removing the MR80 Control Logic PCB and Freq Counter Assy.. taking into consideration it's winter where indoor air is dry? We have a furnace device that flows hot water onto mesh to inject humidity. It does a good job holding RH indoors above 50% with no sparks when touching wall switches, etc.

Do I need antistatic bags, a wrist strap or special bench mat for these tasks?


-Gregory
 
Today's tuner test

Today I decided to power-up and test the MR80, which has been sitting on the shelf since April 7th when C313, an NP cap was replaced on the Control/ Tuning PC board. The new C313 is seen in the photo below:

MR80_NP.jpg

The MR80 has been running on the bench with a cheap folded dipole antenna for over THREE hours and the DISPLAY is STABLE. :banana:

MR80_stable_07.jpg

Previous to this new cap, the MR80 display would start ranging in less than a minute.

If this keeps up for another few days... then I'm going to declare it FIXED.


-Greg
 
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Great stuff, glad to see you got it sorted (or at least at this point), simple fix too......:thmbsp:
 
kevzep said:
Great stuff, glad to see you got it sorted (or at least at this point), simple fix too....
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What no one heard about was that I broke a trace on the top side of the PCB pulling that cap. It was a blind trace, and the only way to know there was a trace hidden underneath the cap was to first check the PCB diagrams--both sides.. or have experience recapping that board.

It's good feeling to have TWO power supply boards recapped now. :thmbsp:


Still could use new touch-tuning springs and a professional checkup/ alignment.


-Gregory
 
Gregory said:
What no one heard about was that I broke a trace on the top side of the PCB pulling that cap. It was a blind trace, and the only way to know there was a trace hidden underneath the cap was to first check the PCB diagrams--both sides.. or have experience recapping that board.

It's good feeling to have TWO power supply boards recapped now. :thmbsp:


Still could use new touch-tuning springs and a professional checkup/ alignment.


-Gregory
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Oopps......Double sided PCB is it?

Yes its all reassuring isnt it when you know its all done......

What is the symptom when these preset springs are a problem?
I use the presets all the time on mine and they seem very reliable.....at this point at least.
My unit has been to Terry for a recap and audio path upgrades...
 
kevzep said:
Oopps......Double sided PCB is it? What is the symptom when these preset springs are a problem? I use the presets all the time on mine and they seem very reliable. My unit has been to Terry for a recap and audio path upgrades...
Click to expand...

The right-most touch sensitive button (out of four total) is unresponsive some or most of the time. IIRC there were one or two intermittent touch controls back in the 80's when I bought it, so it's always been like that. Patrice may chime in and explain. BTW I called Terry a month or two ago and he said something like they typically don't need a whole lot of re-adjustment.. but can't remember what he said for sure. :scratch2:


Edit.. BTW it ran for over four hours this afternoon without malfunctioning.


-Gregory
 
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