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Author Topic: Tempo 2020/8010  (Read 3402 times)
KOP
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Posts: 338




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« on: January 30, 2018, 01:41:02 PM »

So once again we're back to the infamous Tempo 2020. When we last visited this hybrid backwater I was adding a remote VFO . Many thanks to @N4PL Wald ,  @W7CPA  Randy , bajapac , and Fantom the wonder dog...
The molex plugs are common and available locally. Possibly because of not having to deal with the heat of the radio the external VFO has far less drift than the internal VFO.
Now onto other irrational and unexplained behavior.

Ever seen a switched RCA jack? Any of us with 2020's have. That wasn't it. The headphone jack wasn't it. The phone patch wasn't it. I quit looking and found receive audio at the card edge connector and called it a day.
Now on to the unscheduled programming.
RF derived ALC should not clamp a pair of 6146's down to 20 watts output. For testing purposes D362 on the PC-078 IF board has been lifted interrupting the ALC signal from Q1001 on the PA board. Full output results.
With an annoying hum. I'm chasing the audio down looking for an audio or ground loop. Temporarily using my MC-50 for a High impedance mic . Most of the hum goes away but it is still visible (and audible) on a nearby web sdr.

Several questions arise from the service manual and schematic. R388 on the PC-078 IF board appears to adjust the meter ALC, does R387 adjust the actual ALC ?

I wonder if increasing the feedback resistor, increasing the gain of the audio chip has anything to do with the hum.
PC-080 card, replace R551 with a 15k resistor instead of the 6.8K . Great gain improvement but ...

So  If any of this makes any sense I'd appreciate the input.
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I considered a microwave oven magnetron and a 4' dish as a drone-killer. The ERP would be on the order of a hundred thousand watts or so. ~anon

November 28, 2018, 09:16:04 AM
N8CBX
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Posts: 561




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« Reply #1 on: January 31, 2018, 02:42:22 PM »

I use the external 8010 VFO with my 2020 and use the 2020 daily. Yes, its very stable.
You lost me on the switched RCA jack question(?).
Jan N8CBX
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Dayton Ohio - The Birthplace of Aviation
KX4OM
Member

Posts: 351




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« Reply #2 on: January 31, 2018, 04:27:54 PM »

So once again we're back to the infamous Tempo 2020. When we last visited this hybrid backwater I was adding a remote VFO . Many thanks to @N4PL Wald ,  @W7CPA  Randy , bajapac , and Fantom the wonder dog...

I assume you have gleaned everything you can from the Tempo 2020 Yahoo group, then. The high resolution color coded schematics and individual board descriptions that Wald, N4PL and I put together, and the cobbled together and annotated Level Diagrams (stage gain diagrams) in dBm and dBv for transmit and receive.

You have then seen the various ways of dealing with the cracked sprockets. Definitely not a unique problem; all the hybrids that use them are affected. The source of replacement sprockets (SDP-Si) stopped selling the Delrin ones I used, along with the matching ladder chain sizes. I was not aware that Greg, NR6C was producing the excellent printed replacement sprockets last year until Wald, N4PL showed me a sample. Greg and I exchanged emails since then. His are much sturdier than the glued Delrin sprocket on a small brass hub ones from SDP.

I have a couple of comments on the ALC. I built a 2-tone generator, the one in the ARRL test procedures manual to set the ALC. The generator in my old HO-10 isn't cutting it anymore, but the scope is fine. It is in the Tempo 2020 docs to do it that way. After setting the level accurately with the two-tone, the ALC is still tweaky, but less so than the all or nothing it seemed to be. Wald has since clued me in to the need for better mic amplification, which he has solved in his 2020s. I have not had hum issues. It has always appeared to me that the ALC is "set and forget" in other words, not active except to signal to a linear amp to dial it back. For the 2020 user, just keep the mic audio from driving past the red band, since you've calibrated that with the tone generator. I think that is the way it works.

I no longer have my set of spare boards and other parts to swap in and check/troubleshoot. I passed those on once I got mine to where I thought it should be. I had some boards that were from my particular version of the 2020, and some from the other version, the newer one. Mine is Serial#6080118, with Manu-Vox-PTT and Fast-Off-Slow. It uses the PC-079 AF board, and the PC-156 board of the later version is not directly swappable. Mine does not have the really good IF trap of the newer units.

I check the Yahoo group every couple of weeks, but it is not nearly as active as it used to be.
 
Ted, KX4OM

« Last Edit: January 31, 2018, 04:51:40 PM by KX4OM » Logged
N8CBX
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Posts: 561




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« Reply #3 on: January 31, 2018, 05:37:37 PM »

The source of replacement sprockets (SDP-Si) stopped selling the Delrin ones I used...
Ted,
I think the SDP/SI sprockets & chain are available. I haven't check their stock lately, but I used their sprockets/chain in my three 2020 rebuilds.
Jan N8CBX
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Dayton Ohio - The Birthplace of Aviation
KOP
Member

Posts: 338




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« Reply #4 on: January 31, 2018, 08:29:52 PM »

Jan,
      My understanding is that the external speaker RCA jack turns off the internal speaker when a plug is inserted. Actually I wouldn't know as the Jack has never had audio present. Again the headphone jack turns off the internal speaker when the plug is inserted but I wouldn't know for sure because there has never been audio present here either. I traced receive audio as far as the card edge connector and attached a speaker wire there. I still have no audio at either jack. I'll admit it was an easy fix but a kludge in any case.
     
Ted,
     I'm sure I haven't read everything about the Tempo 2020 but between you, Wald, Randy and rest of the Yahoo list I haven't missed much. Thank you for all the files and anecdotal information. The combined experience of all the owners of the Tempo 2020 is greatly appreciated.
     I think I've found a unique issue that only at the moment presents a puzzle. It isn't RF derived that I can tell and the near 120cy spacing points to a power supply filtering issue. As Wald suggested I used a variety of mic elements ranging from a 500 ohm CB mic, A Shure 444 element (520D actually) in high and low impedance, a crystal element and my MC-50 in low and high impedance.
The results were the same. Starting at 180+Hz , 120Hz apart, as many as five distinct lines down the waterfall.
      This all started with the R551 change and has persisted regardless of microphone. The ALC issue was pronounced and definite. 20 watts from a 12BY7A and 6146 pair that had produced 110wats in the TS-830S. The 12BY7A and pair of 6146's that came out of the Tempo are producing 120 watts on 80m in the Kenwood. I wanted to see id there was a glaring bias error or drive issue so I intercepted ALC at D362. I now have nearly 110 watt output on 80m , and a hummmmm.
       Back to square one as soon as I can steal the time. Re-connect D362. I can't bring myself to change R551 back as the mic gain was ultra conservative. I had to scream at any mike to get any needle deflection on internal or external meter. There was however no reported hum. I'm aware of the schematic confusion regarding the mic wiring. It is what it is.
       There won't be any progress for a few days while life interferes. I'll go back and do the ALC procedure by the numbers. I'll look for ripple in all the wrong places. I'll even replace the mic element with a 50k ohm resistor.

... and with that I'll go looking for the dinah-moe humm 
Logged

I considered a microwave oven magnetron and a 4' dish as a drone-killer. The ERP would be on the order of a hundred thousand watts or so. ~anon

November 28, 2018, 09:16:04 AM
KX4OM
Member

Posts: 351




Ignore
« Reply #5 on: February 01, 2018, 09:29:10 AM »


     I think I've found a unique issue that only at the moment presents a puzzle. It isn't RF derived that I can tell and the near 120cy spacing points to a power supply filtering issue. As Wald suggested I used a variety of mic elements ranging from a 500 ohm CB mic, A Shure 444 element (520D actually) in high and low impedance, a crystal element and my MC-50 in low and high impedance.
The results were the same. Starting at 180+Hz , 120Hz apart, as many as five distinct lines down the waterfall.

You could take a look with a scope for noise at the +12 VDC at the 3, 8, and 13 socket pins on the AF card 079 or 156, whichever you have.  All of those Zeners and their transistors in the AVR unit, maybe some oscillation at the line frequency and harmonics.

Ted, KX4OM
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KX4OM
Member

Posts: 351




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« Reply #6 on: February 01, 2018, 10:29:54 AM »

Jan,
      My understanding is that the external speaker RCA jack turns off the internal speaker when a plug is inserted. Actually I wouldn't know as the Jack has never had audio present. Again the headphone jack turns off the internal speaker when the plug is inserted but I wouldn't know for sure because there has never been audio present here either. I traced receive audio as far as the card edge connector and attached a speaker wire there. I still have no audio at either jack. I'll admit it was an easy fix but a kludge in any case.
     
It used to be easy for me to scope out this type of thing when I had a couple of spare units stacked naked in the closet Smiley  Looking at the schematic, the RCA jack ("phono" to some) for the Phone Patch connects directly to the AF out pin of the AF card. It may actually do that by way of the Phones jack for convenience. Anyway, there should be audio at the RCA jack if the wiring to the dual-switch Phones jack has not been messed with or broken. The External speaker jack is in series from the Phones jack, and the Internal speaker is in series from the External speaker jack. There is a minimum load/voltage divider in the Phones jack circuit, consisting of a 56 ohm resistor and a 10 ohm resistor. I don't recall the spec for the external speaker.

Maybe a previous owner did something creative with the Phones jack circuit like trying to make it work with his stereo headset.

Ted, KX4OM
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KOP
Member

Posts: 338




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« Reply #7 on: November 02, 2018, 06:08:01 PM »

schematic ref. uF V Digi-Key P/N
C601, C603 33 200 4179PHBK-ND
C602 1 160 493-1157-ND axial, not available as radial
C12, C13 220 500 493-4357-ND
C11 220 400 P6850-ND
C09, C10 3300 80 P7509-ND

I'm just going to bite the bullet and shotgun the filter caps, on all three radios. Yes , three. I put one under the bench and when I pulled it out there were three. Well , not really but you know how these things go .

c87 breakdown
Logged

I considered a microwave oven magnetron and a 4' dish as a drone-killer. The ERP would be on the order of a hundred thousand watts or so. ~anon

November 28, 2018, 09:16:04 AM
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