Yes, they can be found. Discussions here: /g/DRAKE-RADIO/search?p=created%2C%2C%2C20%2C2%2C0%2C0&q=promIn short, the PROM is a clever band segment edge detector that disables the UP or DOWN buttons when you reach a segment edge. The inputs (address lines) connected to the N-code bus are likely ESD sensitive when handling the DR7. You can actually remove the PROM from the DR7 and the rig should operate normally. The only difference will be that you can traverse beyond the segment edges with the UP/DOWN buttons. You should not transmit beyond the limits or you risk higher out of bad emissions or damage to the LPF module. On Tue, 08 Apr 2025 04:27:00 -0700 "Diego Gallo via groups.io" <lu3hdd@...> wrote: We¡¯ve identified the root of the problem as the PROM memory (U9003) (MMI 6300), which has two inputs shorted.
I would greatly appreciate any information regarding this component, particularly the data it contains. Additionally, if this memory is no longer available on the market, does anyone know of a compatible replacement? -- 73 -Jim NU0C
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Re: Drake 2-C AVC Voltage Problem
That didn¡¯t work as well with the ECL I used to work on. They all were warm. You could, however, eyeball a backwards ECL chip, as they¡¯d actually glow! (You could also just look for the notch :-) ?)
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Mon, Apr 7, 2025 at 21:09, jerry-KF6VB < jerry@...> wrote: On 2025-04-07 17:53, Jim Shorney via groups.io wrote:
> He wasn't a seasoned tech if he didn't know about the calibrated finger
> test.
*** The *ouch - sizzle* test.
- Jerry, KF6VB
>
> On Mon, 07 Apr 2025 16:01:38 -0700
> "jerry-KF6VB via groups.io" <jerry@...> wrote:
>
>> .... I was working as a tech in a telephone equipment factory. We
>> were
>> building a 24-bit telephone switch. Large boards stuffed with
>> rectangular
>> arrays of TTL ics.
>>
>> One "tech" had a unique and simple way of "troubleshooting".
>
>
> --
>
> 73
>
> -Jim
> NU0C
>
>
>
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Re: Tuning a pi-Network Output
Yes, it needs to be the value shown in the schematic, in parallel with the variable. Substantially higher values are not recommended and the original values should be used if you¡¯re not using RCA tubes.?
I¡¯m just getting up and so don¡¯t have the manual in front of me and can¡¯t remember the exact values.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Mon, Apr 7, 2025 at 19:53, n4buq < n4buq@...> wrote:
Regardless of how I go about it, with C77 in place, C76 minimizes the output at fully open and with C77 disconnected, C76 minimizes the output at fully closed.
With one leg of C77 disconnected, I started checking its value and I kept getting very weird values: either several microfarads (yes with a "micro") or somewhere around 140 picofarads.? I decided to de-solder the other end and checked it again and it went complete to "Unknown or damaged part" on my T7 component checker.? Apparently it was on the verge of completely bad and de-soldering finished it off (short lead on one end).
I don't have a proper replacement yet but I do have a 27pF 500V SM that I might throw in there just to see if changes things much the same way the original cap did.? I presume it will still be too much extra capacitance but it might be interesting to see, with it in circuit and even though it's about double the original capacitance, whether C76 gets the output closer to a full null when it's at or nearly fully open.
I presume a disk ceramic is still the appropriate cap to use for C76?
Thanks,
Barry - N4bUQ
Steve,
I'll run through it that way.? As I said, all I did was monitor the output at the antenna jack with no dummy load.? Since the controls didn't seem to affect what I was seeing on the scope.? Perhaps it was mostly due to there not being a proper load resistance.? I'll report back - hopefully tomorrow.
Thanks so much!
Barry - N4BUQ
Just to check, the transmitter should be tuned for a dip at the highest frequency or where specified by the procedure. You then leave the plate and load controls as they are, then disconnect the screen supply. Then, after disconnecting the screen supply, go into transmit with the minimum drive to see a reading on the scope. The transmitter remains connected to the dummy load. Adjust the neut cap for minimum amplitude. Reconnect the screen supply and verify that max power out coincides with plate current dip.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Sun, Apr 6, 2025 at 17:01, n4buq <
n4buq@...> wrote:
Yesterday, I disconnected the screen grid supply to the PA tubes and monitored the output at the antenna jack with my scope.? While I can see a reduction in what appears to be the spurious oscillation, that occurs at the point where C76 is fully open (which might explain why it was in that position when I saw it earlier).? I find this odd and likely a problem.? Unlike needing to change C77 just a bit for some of the tube brands, it appears there's already way too much there.
I disconnected C77 and that didn't have much, if any, affect on the value I'm seeing across C76.? That reading is somewhere around 40 nF which I think may be very much out of line as to what it should be.? Changing the band switch, varying the tune control, and varying the plate circuit caps had little, if any, affect on that capacitance value.? Disconnecting the plate connections also didn't change it much, if any.
Does that reading make any sense?? I'm thinking it doesn't and something else is very wrong but I'm at a loss to explain it.? Is what I'm seeing completely abnormal?
Thanks,
Barry - N4BUQ
Mike,
I've read where there are some circuits that can have individual circuitry for each band that allows for "tweaking" the neutralization on each of the lower bands.? Of course, the Drake circuits don't have that but I presume it is possible.
I'm currently only using the watt meter in my MN-2000 for CW as I don't have a mic wired up for the TR-4 yet.
Thanks,
Barry - N4BUQ
Barry and Steve,
?
Neutralizing an RF amplifier is occurs ONLY on the frequency
it is performed on. This typically is done on 10 meters on an amateur
radio transmitter/transceiver final amplifier.
?
Once the neutralizing adjustment is performed on 10 meters, do NOT
make any changes to the neutralizing circuit on any lower band. You
will not see the same maximum RF output at maximum PLATE current
dip on any lower band. This is NORMAL and should NOT mean you have
to make changes to the neutralizing circuit on the lower bands.
?
Follow the manufacturer's transmitter loading/tuning instructions
in the operator's manual.
?
The Drake MN-2000 watt meter is an "average watt meter". Do not
expect to see "SSB PEP" RF levels on the MN-2000 watt meter.
?
73
Mike W5RKL
?
?
?
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Hello, friends,
I have a TR7 that initially exhibited display issues¡ªrandom numbers appeared with dim brightness, and none of the bands were operational. After consulting with the forum and following the recommended steps, I inspected and cleaned all the unit¡¯s contacts, but unfortunately, there was no noticeable improvement.
Some time later, a friend and I resumed the repair process. After checking various components, we traced the issue to the DR7 board, specifically the U9022 counter (MC14518B). Upon replacing it, the display began to show the correct frequency. However, only three bands are currently working (1.5 ¨C 2.5 and 28.5 MHz).
We¡¯ve identified the root of the problem as the PROM memory (U9003) (MMI 6300), which has two inputs shorted.
I would greatly appreciate any information regarding this component, particularly the data it contains. Additionally, if this memory is no longer available on the market, does anyone know of a compatible replacement?
Thank you in advance for any assistance.
Diego Gallo ¨C LU3HDD
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Re: TR-4CW S meter stays to the right
Mark-
?
I would echo what others said; sounds like you were in transmit mode. Hard to blow a supply fuse in receive unless something's really wrong.?
?
If you have doubts about the power supply, then stop everything that you're doing until you fully check it out.?
?
There is a really great article on the WB4HHN site which will help you identify if you have all of the required voltages. You can disconnect the supply from the radio and use the cinch/jones jumper to turn on the supply. Be really careful since you are dealing with B+ and screen voltages. Even if the AC-4 has been rebuilt by someone else, those same voltages should be present on the correct pins. The bias supply is negative, as well.?
?
Be systematic about it. As they say, "slow is smooth, smooth is fast."?
--
Craig/W8CS
Greenville, SC
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Re: T-4XC Meter Shunt Resistor?
Thanks Dan & Peter!
?
R49 came in at around 1600 ohms, replacing tomorrow. Surprisingly, Amazon has them but you have to buy in bulk. I just received the unusual message after my order,?
"Your order for 10PCS 1.5K Ohm Resistor from FOCMKEAS has been confirmed"
Can't wait to read the review comments with a vendor name like that.?
?
I'm replacing the 3.3 ohm with a precision 1% and I'm going to run leads from it to banana jacks that I'm installing in the extra holes next to the cinch jones connector.?
?
At 60mA bias I should read a drop of .198V across the jacks. With that funky non-zero meter in the T-4, I wonder what the actual bias is that I'm currently running.?
?
Hopefully the extra wire length won't create any parasitic hooligans.?
--
Craig/W8CS
Greenville, SC
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Drake didn¡¯t make the receiver but made that for some other receiver.(my guess) Plainly marked for 915KHz. A real rare piece I think. ?Same looks as the old phone patch.
73, Gary WB6OGD
toggle quoted message
Show quoted text
On Apr 7, 2025, at 9:09?PM, Robert Eckweiler via groups.io <af6c@...> wrote:
? There's been no response to my post. I think this is because Drake never made such a receiver. this question arose from this listing on eBay for a 'RARE' :
?
?
Either it is a typo, or the unit has been modified for 915 KC, which ,to most of us, makes it rather useless.
?
Bob, AF6C
|
There's been no response to my post. I think this is because Drake never made such a receiver. this question arose from this listing on eBay for a 'RARE' :
?
?
Either it is a typo, or the unit has been modified for 915 KC, which ,to most of us, makes it rather useless.
?
Bob, AF6C
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Re: T-4XC Meter Shunt Resistor?
Totally agree with Dan on R59, the 3.3 ohm shunt resistor.
That resistor...and R49, the 2w 1.5K ohm resistor on the 250V line just above it, are often found heat damaged in the T-4XC, and I usually change them whenever a T-4XC comes my way....just because.? Your R49 looks slightly bulged around the middle to me in?your pic.? ?Check it at the very least.
73 Peter VE7PS
Yes.
Dan WB4GRA ? I'm looking to replace the 3.3ohm meter shunt resistor in the cathode circuit of my T-4XC.?
?
Is the circled resistor the right one??
--
Craig/W8CS
Greenville, SC
<shunt.jpg>
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There's a reason why Mother's Day happens a week before Hamvention ? 
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Re: Drake 2-C AVC Voltage Problem
On 2025-04-07 17:53, Jim Shorney via groups.io wrote: He wasn't a seasoned tech if he didn't know about the calibrated finger test. *** The *ouch - sizzle* test. - Jerry, KF6VB On Mon, 07 Apr 2025 16:01:38 -0700
"jerry-KF6VB via groups.io" <jerry@...> wrote:
.... I was working as a tech in a telephone equipment factory. We were
building a 24-bit telephone switch. Large boards stuffed with
rectangular
arrays of TTL ics.
One "tech" had a unique and simple way of "troubleshooting". --
73
-Jim
NU0C
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Re: Another TR7 Journey begins
On 2025-04-07 17:52, Jim Shorney via groups.io wrote: Sort of like people
drilling a hole in their iPhone because they were told that Apple
"forgot" the hole for the headphone jack. *** Were these the same people who complained when the motorized cupholders on their PCs broke? - Jerry, KF6VB
|
Re: Drake 2-C AVC Voltage Problem
On 2025-04-07 16:33, Lynn KB6OKS via groups.io wrote: That was when chips and girls were affordable....maybe he was on to something!
Lynn WR7G *** I don't remember girls ever being affordable.... - Jerry, KF6VB
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Re: Drake 2-C AVC Voltage Problem
He wasn't a seasoned tech if he didn't know about the calibrated finger test. On Mon, 07 Apr 2025 16:01:38 -0700 "jerry-KF6VB via groups.io" <jerry@...> wrote: .... I was working as a tech in a telephone equipment factory. We were
building a 24-bit telephone switch. Large boards stuffed with
rectangular
arrays of TTL ics.
One "tech" had a unique and simple way of "troubleshooting". -- 73 -Jim NU0C
|
Re: Another TR7 Journey begins
Reminds me of the sad Pioneer stereo receiver I picked up some years ago. Someone had aerially wired a relay and a 28 pin digital logic chip into the audio PA. WTH? The only thing I could think of was someone was pranking the owner with bogus mods. Sort of like people drilling a hole in their iPhone because they were told that Apple "forgot" the hole for the headphone jack. On Mon, 07 Apr 2025 12:20:04 -0700 "Bill NZ0T via groups.io" <nz0tham@...> wrote: And then there's this mess.? A 10 uF electrolytic cap from antenna positive to ground and the white wire to the R2001 wiper.? Huh?? None of that should be there. -- 73 -Jim NU0C
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Re: Drake 2-C AVC Voltage Problem
On 2025-04-07 17:00, Gary WB6OGD via groups.io wrote: And cost the company ten times that in uneeded
replacement parts! *** Not to mention the possibility of damaging the actual board with wholesale chip replacements- although the rework ladies were VERY good at desoldering & soldering. - Jerry, KF6VB 73,
Gary
WB6OGD
On Apr 7, 2025, at 4:20?PM, jerry-KF6VB via groups.io <jerry@...> wrote:
?On 2025-04-07 16:08, Gary WB6OGD via groups.io wrote:
If he was really high paid guy, I guess that method would make
economic sense... $5.50 an hour. This was around 1978.
- Jerry, KF6VB
But it sounds like he probably was the opposite, hi hi...
73,
Gary
WB6OGD
Links:
------
[1] /g/DRAKE-RADIO/message/84224
[2] /mt/112117533/243852
[3] /g/DRAKE-RADIO/post
[4] /g/DRAKE-RADIO/editsub/243852
[5] /g/DRAKE-RADIO/leave/12260778/243852/767576506/xyzzy
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Re: TR-4CW S meter stays to the right
Check the filter cap for the bias supply. It should have the + terminal connected to ground. Some eBay sellers are offshore vendors ripping off the IP of legitimate sellers and don't have any technical knowledge. On Mon, 07 Apr 2025 17:22:48 -0700 "Mark N2DMI via groups.io" <markkiziuk1@...> wrote: Hi Tim! It has fairly brand new parts inside of the power supply. It cost me good money from someone on Ebay who rebuilds these power supplies with new boards with new parts. Hopefully its not anything to do with the power supply but who knows?
Mark -- 73 -Jim NU0C
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Re: T-4XC Meter Shunt Resistor?
toggle quoted message
Show quoted text
On Apr 7, 2025, at 8:04?PM, Craig W8CS via groups.io <craig_severson@...> wrote:
? I'm looking to replace the 3.3ohm meter shunt resistor in the cathode circuit of my T-4XC.?
?
Is the circled resistor the right one??
--
Craig/W8CS
Greenville, SC
<shunt.jpg>
|
Re: TR-4CW S meter stays to the right
Hi Tim! It has fairly brand new parts inside of the power supply. It cost me good money from someone on Ebay who rebuilds these power supplies with new boards with new parts. Hopefully its not anything to do with the power supply but who knows?
Mark
|
Re: TR-4CW S meter stays to the right
Happened to me years ago and its been long time since I looked at the bottom of a AC4 but as I recall there are two rectangle higher wattage white resistors, one of those was the problem.
73 Tim
WB8UHZ
On Monday, April 7, 2025 at 08:11:02 PM EDT, Mark N2DMI via groups.io <markkiziuk1@...> wrote:
Not to my knowledge? I am very new to Drakes. There are settings for VOX and anti-VOX which to be honest might not be set right?
I'm still trying to tune this thing up. As a matter of fact, I tuned up on 40 and 20 then went to 80. When I was at 80 is when the problem kicked in.
I believe I was tuning it up correctly? Then the S meter started to go to the right and stay there with no sound.
Then as I adjust the RF gain metal finger lever it will not do anything to the S meter. Then about 2 minutes later the rig shut down. I looked inside the drake and the 2 fuses measure OK so I believe the 5 amp fuse in the power supply blew. I'm not having much luck.
Mark
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Jim Shorney
Craig W8CS
Gary WB6OGD
Mark N2DMI