Tektronix 575 Curve Tracer Repair - Page 1
Forum section: electronics / repair

author: W2DML
author_rank: Contributor
timestamp: September 13, 2025, 05:47:12 am
content: Hello, I recently picked up a beauty of a Tektronix 575. Sad part is, it's not fully functional and will need a repair. Before I deep dive & go through every component, I'm wondering if anyone has some ideas on what could possibly be wrong.The unit powers up but I can't produce a trace. The CRT is on but is only producing a dot. Adjusting any of the horizontal or vertical settings will not move the dot. Another interesting detail I noticed is that adjusting the intensity CW or CCW will make said dot disappear.So far I measured the -150V, 100V, & 300V to be good. Their load impedance is also matching the Tek spec.I used my scope to verify the Collector Sweep is working.This leads me to believe the problem is either in the Vertical/Horizontal Amps or the CRT. I would assume more towards the CRT circuit due to the probability of both amps failing to be low. I currently don't have a HV probe capable of verifying the voltages but shouldn't they be ok since the CRT is displaying the dot, it's just not deflecting in X or Y axis? Additionally V812 & V822 seem to glow.Maybe it's a bad intensity pot?Ty in advanced.Here is the CRT circuit.Here is a link to the manual with schematic diagrams if interested.https://web.mit.edu/6.101/www/reference/tek_575_manual.pdf

author: perdrix
author_rank: Frequent Contributor
timestamp: September 13, 2025, 08:34:52 am
content: Silly question: Have you confirmed that the leads from the H and V output amplifiers are connected to the deflection pins on the CRT?David

author: W2DML
author_rank: Contributor
timestamp: September 13, 2025, 12:08:15 pm
content: Hi David,They look connected, I will do a continuity check to see if that is the reality. My next plan was to probe the signals on a scope, I would expect to see a horizontal sweep at least.

author: mawyatt
author_rank: Super Contributor
timestamp: September 13, 2025, 01:33:16 pm
content: Don't have a 575 but a 577 (which was repaired) so notes are relative to such.Since you can see the CRT dot and control the intensity this indicates the HV Grid circuits are working.As you don't see the dot being swept horizontally check the sweep circuit and sweep voltage across the Horizontal CRT plates. On the 577 this isn't that high a voltage and the Horizontal driver on the 577 was a transistor circuit for both Horizontal and Vertical on the same PCB. Recall the transistor circuit was relatively simple and the same for H and V with only a few transistors.Best

author: W2DML
author_rank: Contributor
timestamp: September 13, 2025, 11:00:09 pm
content: So thanks to Pedrix I was able to fix problem #1 of the Tek 575. Apparently the leads to the deflection & geometry were touching the metal housing. I bent the leads and this ended up removing the short between them.Now to the next challenge, I am able to have full beam with control from the horizontal & vertical amps. My collector sweep is working well but the base is not. I will now deep dive the manual to see what Tek recommends to do.

author: factory
author_rank: Super Contributor
timestamp: September 14, 2025, 01:11:05 pm
content: Something is not right with that, the pins should be in the middle of the cutout, either the CRT has slid back (maybe due to broken clamp) or someone changed it for another type?David

author: W2DML
author_rank: Contributor
timestamp: September 16, 2025, 01:51:50 am
content: So further updates have led me to the step amplifier. The step generator works & matches the recommended spec. Once we enter the step amplifier section is where we have problems.Currently I don't see any busted components. I swapped all the tubes in the section. The +/- 15V supply looks ok, it's not a perfect 15V but close enough.When following the schematic's control settings to match waveforms, I do not get what Tek gets. For example the grid of the difference amplifier at R224 is not a 0 to -3V staircase, it's a triangle wave that is around -3V. It seems whatever is converting the steps, is not doing so. This makes sense as when testing with a transistor we only see 1 line, no matter how many steps/family we select. Does anyone have any ideas?

author: W2DML
author_rank: Contributor
timestamp: September 16, 2025, 01:53:43 am
content: Quote from: factory on September 14, 2025, 01:11:05 pmDavid,It looks like this was a functional unit that was serviced up until some time. The CRT looks original but could have been replaced.

author: factory
author_rank: Super Contributor
timestamp: September 16, 2025, 05:06:56 pm
content: OK I'm not sure you understand my post.Thinking about it another way, is there a large gap between the front face of the CRT, the scale plate and/or the bezel?Below is a picture from Tekwiki, showing how the pins are centred in the shield cutout, this is how it should be, bending the pins wasn't a very good idea, as it could have cracked the glass, you were lucky.Note that the CRTs in the 570 & 575 are often destroyed (necked) by shipping, anyone thinking of buying one should pick it up in person.David

author: W2DML
author_rank: Contributor
timestamp: September 16, 2025, 09:42:36 pm
content: David,I appreciate the help and advice. I understand what you're saying. I finally had a chance to look at the CRT. It definitely had room for movement, I adjusted it to be proper. Again appreciate the help. Luckily I didn't bend the pins too much.I recently bought this not working for $100 so I'm unsure the full history of the unit.On another note, I discovered the 2n777 pnp transistor is shorted between the collector and emitter. I believe this is part of the problem, I am planning on replacing it next. I've verified other parts of the step amplifier to be working and the symptoms makes sense to this transistor being the problem.

author: cncjerry
author_rank: Unknown
timestamp: September 20, 2025, 05:48:11 am
content: Is this the one that was for sale on craigslist? In san francisco area? I remember it being a really good deal.

author: W2DML
author_rank: Contributor
timestamp: September 21, 2025, 06:28:42 pm
content: Quote from: cncjerry on September 20, 2025, 05:48:11 amThis one was from Marketplace in the Massachusetts area.More updates! I swapped the defective transistor and was able to restore the sweep of the base. At a high number of steps the display started to flicker, unsure if this is normal. I then proceeded to do the calibration where I got far but had some display issues. I think I need to check the -1500V supply, which requires a HV probe. I ordered a fluke probe & will verify, adjust the voltage then. I think the bad voltage might explain the weird behavior I have with the intensity pot, etc. I also noticed some switches are dirty or defective, will most likely have to replace those.