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Free 120-120 transformer, on Facebook, in Fayetteville AR
Not a big fan of Facebook (but I'm interested in Meta AI...so...)
Anyway, this was posted, recently, in the "Vintage Electronic Test Equipment" VETE forum/group, on Facebook. Anyway... if it was me... and even though I'd like to get it... it's not going to be. I'd offer him a few bucks for it... especially if he has to USPS it. Remember, it's on Facebook, it in AR, and it's heavy. -- Roy Thistle |
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Re: Tektronix 547 Lack of Sweep or Intensity Control
Here's the datasheet for the CRT - it may help.
I have exactly the same issue as you & have checked everything I can think of, I'm sure there's more going off here than a bust CRT. I've not had this issue before with my 545B & 585A so think it's something to do with the 547 circuitry, this is my gut feeling but could be wrong. I've not worked on mine for a while but was going to try tacking on a resistor/pot combination off R857 IE the cathode supply instead of the current intensity pot to g1. We only need a -65v to -95v difference between cathode and control grid to vary brightness. Crude but worth a try before righting off the CRT. Andy. |
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Re: can you identify this rumored to be tek part?
Thanks for looking into this¡ªgood to know that those are fuses.
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He should definitely hang onto those¡ªalmost every 7A19 I¡¯ve acquired either has no spare fuse, or no working fuses. He¡¯s found the mother lode! Tom Sent from an iThing; please forgive the typos and brevity On May 10, 2025, at 18:26, Adam R. Maxwell via groups.io <amaxwell@...> wrote: |
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Re: can you identify this rumored to be tek part?
On May 9, 2025, at 23:36 , Tom Lee via groups.io <tomlee@...> wrote: I was curious enough to pull out my mostly-working 7A19 and take a family photo of the fuses and two of the attenuator modules. The two spare fuses and the installed fuse are all marked 0.2 18, so I think John's bag of attenuators is correctly marked! /g/TekScopes/photo/302392/3914925?p=Name%2C%2C%2C20%2C1%2C0%2C0 I didn't feel like removing a screw to take out the other attenuator module. The 7A19 attenuator is easier to work on than the 7A29, but the plugin sits in a drawer because the coupling switch is flaky and I'm afraid of absentmindedly blowing a fuse. Adam |
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Re: 2465B broken Volts/VAR
I recommend not to pull off the plastic knobs as the service manual says and instead slide off the bezel and the button panel off the pots. The knobs get brittle and break off easily. Otherwise service manual steps are very thorough. Here is an album to explain it better with pictures.
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/g/TekScopes/album?id=259435 Ozan On Sat, May 10, 2025 at 01:09 PM, Mike Enkelis wrote:
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2465B broken Volts/VAR
I have a 2465B with a broken Volts/VAR shaft and am asking for second opinion on replacing
The shaft. My first thought is to pull the front panel out following service manual. Then proceed to the POT module removal process as described in service manual to Gain access to the broken shaft for removal from the actual variable pot. Install a replacement shaft, then reassemble everything. I have a dead 2465A for parts doner that I plan on practicing on first. Is there a simpler solution for what I need to do? After the shaft is replaced, I plan on recapping the LVPS and then replacing the surface mount electrolyte capacitors and DS chip on the A5 board. |
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Re: Looking for rear feet for 2465 DVM scope
Hey Jason,
If you're diagnosing this scope from scratch, then the first port of call is to look at all the supplies at J119 on the main board. There's a table with acceptable voltages and ripple somewhere in the service manual. You don't need to use an isolation transformer, but you may want to plug both scopes into the same outlet or extension strip to minimize the ground differential. Make sure you perform power supply measurements under the 20MHz bandwidth limit. If you haven't read this document before: , now is probably a good time :). Depending on where in the world you live, 950MHz could be a frequency used by a mobile network. These scopes are quite capable of showing waveforms up to a GHz, though the amplitude is way down, and the triggering gets iffy with my 2467 from ~800MHz. Good luck, Siggi |
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Re: Looking for rear feet for 2465 DVM scope
I'll have to get back to you on that while I check all that out sometime tonight hopefully. I do know that I also see the ripple on channel one, but nowhere near the same amplitude. When I plug a probe in channel 2 the ripple drops down to the same amplitude as channel one. I WISH I could post a pic on here of what I'm seeing. Where would a 850ish MHz signal be at inside the scope? Unless it's picking up something like a RF transmission nearby? If that were so then it should be on both channels? I have so many questions on what's happening. All I can think of to do is clean the attenuators and remove, clean and replace the hybrids and see if that changes anything. That and go through the diagnostic waveforms shown in the service manual and see if anything is off there. Do I need to plug the 2465 into an isolation transformer before doing those tests? I didn't see anywhere in the service manual that says to, but I know that doesn't necessarily mean anything, it could be assumed?
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Re: Tektronix 547 Lack of Sweep or Intensity Control
Gordon,
By getting the voltage you say using a meter, you are making a complete circuit from the negative supply, through the crt acting like a diode in this case, to ground. The rest of the circuit was on the rest of the pins. Pin 6 goes to the focus so you would get an infinite resistance between pin 3 and the focus with pin 3 disconnected from the circuit. There are good crts available online. Get one to make sure you have a good one. Do not part the scope out yet. This model is too good to junk. Mark |
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Re: Tektronix 547 Lack of Sweep or Intensity Control
Hi Mark & Morris:
Update - I isolated pin 3 of the crt by unsoldering the wire at the junction of R830/C829 & C830 and measured the voltage on the wire. It was around -1070V even though it was not connected to anything. Maybe this is expected, I don't know. Unfortunately, I don't know of anyone with a crt checker. Also checked for continuity between pin 3 and the cathode at the junction of R857 and C858 - open circuit. Then checked for continuity between pin 3 and the wiper of focus pot R846 - also open circuit. It doesn't seem to be an internal short in the crt, but it's still strange that the grid at pin 3 is at -1070V when not connected to anything. I think this is now beyond my capabilities, so I may have to consider parting it out :( Gordon |
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Re: can you identify this rumored to be tek part?
On 5/10/25 00:36, Tom Lee via groups.io wrote:
sometimes the attenuators will burn out first to protect the fuse. ?maybe that's why these parts were kept in an envelope in a scope-mobile drawer with a 7904A on it! The 7A19 must have been nearby at one time too... |
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Re: can you identify this rumored to be tek part?
Hi John,
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The 7A29 has no input fuses (thankfully), but the 7A19 does (along with two spares). The 7A19's fuses and attenuator modules share the same form factor. so that they can be inserted into the signal path with the same minimal perturbation of microstrip line impedance. The attenuators don't have fuses (intentionally) integrated with them, but sometimes the attenuators will burn out first to protect the fuse. :( There are three attenuator modules in the 7A19, with 10x, 5x, and 2.5x attenuation factors (gain factors are then 0.1, 0.2 and 0.4, which probably explains the "0.2" seen on the pic of the modules you linked to in your OP). -- Cheers Tom -- Prof. Thomas H. Lee Allen Ctr., Rm. 205 420 Via Palou Mall Stanford University Stanford, CA 94305-4070 On 5/9/2025 10:43 PM, John Griessen via groups.io wrote:
Looks similar, except some different circuitry on the flat side.? The box it was in was labeled as fuses. |
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Re: can you identify this rumored to be tek part?
On 5/9/25 12:19, Adam R. Maxwell via groups.io wrote:
John, those look like 7A19 fuse or attenuator elements. See photos on Tekwiki, or I can take one apart when I get home from work.Looks similar, except some different circuitry on the flat side. The box it was in was labeled as fuses. Is the fus *IN* the attenuator? Are there five or ten kinds? |
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Re: Looking for rear feet for 2465 DVM scope
Jason,
I wonder if the caps inside are going bad even though it appears to work. The oscillation could also be decoupling is too low or not at all. If the original electrolytics are still there, replacing would be best. Condor Audio has a kit. The owner owner is on this group. What Siggi said sounds good. That could be your problem. Dirty contacts will cause weird problems. Mark |
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Re: Looking for rear feet for 2465 DVM scope
On Thu, May 8, 2025 at 8:59?PM Jason B via groups.io <sydbowen=
[email protected]> wrote: I've tried DC balance. I was mistaken on the channel 2 waveform on GND.Interesting. Below 50mV/DIV the preamp amplifies the incoming signal, so it's perhaps within reason that it's amplifying something at the BNC. I guess it might also be oscillating. Have you measured the DC resistance of your inputs? It should be as near to 1MOhm as makes no difference in DC coupling and infinite in AC coupling. What happens: - In 50Ohm coupling? - In DC coupling? - When you connect a probe? - When you connect coaxes of different lengths? - At other attenuation settings? The CH1/CH2 preamp hybrids should be interchangeable (though the calibration is preamp specific, so keep track of which is which), so you might see whether this oddness follows the preamp. It's also possible that the hybrid contacts are oxidized, leading to weirdness, so before you swap them, try just re-seating them and/or cleaning their contacts. |
Diabolical Artificer
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