EMG Characteriscope-Z TR-4805 - repair - Page 1
Forum section: electronics / repair

author: Norbert67
author_rank: Contributor
timestamp: April 28, 2025, 03:23:20 pm
content: Hello guys.I received a hungarian curve tracer EMG TR-4805.I have the service manual too, but unfortunately the schematic doesn´t match the reality.The manual is for the type that has a connector for high current adapter on the back.Mine doesnt have that. Maybe an older model. And there are a lot of differences too.The real problem is that 2 transistors are missing with the heatsinks, and I dont know what should I put in there.If someone encountered these curve tracers or have them at home, a picture or the types of the transistors would help me a lot.Thank You.

author: m k
author_rank: Super Contributor
timestamp: May 01, 2025, 12:52:38 pm
content: is there another similar section?You have horizontal and vertical deflection somewhere.Try to take few more pictures where underside traces are more visible.Now both 47R seems to go directly to transistor legs, but the picture is not clear enough.

author: Norbert67
author_rank: Contributor
timestamp: May 01, 2025, 01:58:10 pm
content: First, thanks for the help. Much appreciated.I try to take shots with some backlighting too so that the traces are visible from the other side.I uploaded the schematic too, but as I mentioned, there are a lot of differences.The emitters are connected together and the 47r resistors going to the bases of the transistors, so I think these were complementary transistors in TO-220 package, but the pins are not in row, but more like TO-5 or TO-39.

author: Norbert67
author_rank: Contributor
timestamp: May 01, 2025, 02:01:27 pm
content: More pictures

author: Norbert67
author_rank: Contributor
timestamp: May 01, 2025, 02:10:20 pm
content: Mabe this is more visible and the other pic is from the PSU part of that PCB.

author: Norbert67
author_rank: Contributor
timestamp: May 01, 2025, 02:54:51 pm
content: These are schemes for X and Y amps for the vertical and horizontal deflection.I don´t think that opamp on the picture is for X or Y. But it is hard to see because the vert. and hor. signal is reversed by the collector supply rotary switch, and its very crowded with switches and cables.

author: m k
author_rank: Super Contributor
timestamp: May 03, 2025, 01:51:57 pm
content: So heatsink screws have wider traces, emitters are shorted and go to uA741 inputs and output goes to both 3rd pins through 47R.My guess is a load of some sort.

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: May 04, 2025, 05:43:03 pm
content: Quote from: m k on May 03, 2025, 01:51:57 pmHello Norbert67,Yes, on the PCB, UA741 OPAMP output (pin 6) goes toward 2 x 47 Ohms resistors.I could not find this part of the circuit on the 3 documents you provided.Do you have additional schematics ?

author: floobydust
author_rank: Super Contributor
timestamp: May 04, 2025, 06:20:42 pm
content: The pinout looks like E-C-B, which is odd. Implying TO-126 or Japanese transistors. TO-39 can is E-B-C.The aluminium standoffs are some kind of missing heatsink?It looks more like this is the oscillator and driver for the DC-DC converter? Not the CRT deflection circuit.

author: Norbert67
author_rank: Contributor
timestamp: May 05, 2025, 01:06:41 pm
content: This is the whole manual, if something is not readable, I can scan it.https://elektrotanya.com/emg_typ_1575_tr-4805.rar/download.htmlThe 2 wide traces (collectors?) are connected to the +/- supply rail.First I tought that these are the tr501 and tr502 transistor, but the circuit is completely different.

author: Norbert67
author_rank: Contributor
timestamp: May 05, 2025, 02:43:58 pm
content: Quote from: floobydust on May 04, 2025, 06:20:42 pmFinally I located the TR502 transistor, its not a BD242A but MJE15031, and its bolted to the metal frame. That transistor is BCE, and I think there is a possibility they used a MJE15031 with a MJE15030 or similar here as well. I dont know how they fitted them to the heatsinks though. I believe that the IC on the picture will be the IC501. I hate to admit but the purpose of that integrator is not completely clear to me. Is it for stabilizing the Z intensity of the CRT by synching to the blanking (or other ) pulses?

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: May 05, 2025, 03:28:23 pm
content: Quote from: Norbert67 on May 05, 2025, 01:06:41 pmI downloaded the rar archive from elektrotanya but there's no schematics anywhere. Only user manual and theory of operation.Do you have additional schematics ? (other than the three you already provided)

author: Norbert67
author_rank: Contributor
timestamp: May 05, 2025, 04:05:12 pm
content: Quote from: timeandfrequency on May 05, 2025, 03:28:23 pmSorry, wrong link.https://elektrotanya.com/emg_tip1575_tr4805_characteriscope.pdf/download.html

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: May 05, 2025, 06:37:22 pm
content: Hello Norbert67,Unfortunately, there's still no match between your board and the latest download.In the latter, the OPAMPs part numbers are '741PC' and '?09PC' (IC401), which have likely 14 pins and output is at pin 10.On your board where two transistors are missing, the OPAMP is a vanilla 8 pins (DIL-8 package) 'LM741', having its' output at pin 6.Your unit must be slightly different or the schematics of the assembly including the 'LM741' was not published.

author: floobydust
author_rank: Super Contributor
timestamp: May 05, 2025, 08:03:08 pm
content: You can see the PCB footprint is for uA709 DIP-14 but they changed to 741 DIP-8 in the middle. I didn't know you could drop in a 741 in place of 709.OP can you tell us where the thick PCB traces go? From the collectors of the missing transistors? What is weird is both transistors are driven by the one LM741 output, at the same time.The service manual has some small PCB's on page 71 of 72. I wonder if that is what is missing?

author: Norbert67
author_rank: Contributor
timestamp: May 05, 2025, 08:16:48 pm
content: Quote from: timeandfrequency on May 05, 2025, 06:37:22 pmYes, I mentioned in the first post, that there are differences between the manual and the actual PCB.And yes, there are holes for a 14 pin variant LM709 (these curve tracers are from 1980s, from the eastern block and the component supply was limited).That doesn´t matter, You can substitute a 741 because pin 1,2,7,8,13 and 14 on the 14pin 709 were not connected.https://media.digikey.com/pdf/Data%20Sheets/Texas%20Instruments%20PDFs/LM709.pdfI am not an expert on repairing CRTs, but as I see it, there is a trigger pulse going to the pulse transformer coming from So3/c5 which connector I dont have, but the signal probably coming from the step generator (and i think its a 50Hz gated squarewave). Through the transformer T502 and transistor TR503 (and other passive circuitry) its fed back into the IC501s +input. The opamp acts as an integrator and creates a sawwave and through the 2 missing complementary transistors its connected to the T501 transformer, which creates 2 secondary voltages: the anode HV and one for the heater. Because the primary voltage is much lower (around 20V), the opamp can lower both the anode and the heater easily to blank or lower the intensity when the ray returns and starts a new cycle.This is my hypothesis.But please, correct me if thats completely wrong.

author: Norbert67
author_rank: Contributor
timestamp: May 05, 2025, 08:26:52 pm
content: Quote from: floobydust on May 05, 2025, 08:03:08 pmI think I have written before that the thick traces - collectors - are going to the +15 and -15V.The opamp drives the transistors and the transistors must have to be supplyed from a +/- voltages to not saturate the transformer.

author: m k
author_rank: Super Contributor
timestamp: May 08, 2025, 06:12:29 pm
content: What transformer?+/-15V from where exactly, from under blue capacitor triplet but then what?Yellow/White twisted pair powering the IC is sourced from where?Two series resistors near the board edge and middle point going to IC pin 3.Twisted pair is blocking the corner end of 2nd resistor, were it goes?

author: Norbert67
author_rank: Contributor
timestamp: May 08, 2025, 07:17:08 pm
content: Quote from: m k on May 08, 2025, 06:12:29 pmThe circular one.The +/-15v from the stabilizers 7815 and 7915 and their reservoir caps C504 and C505 (big ones with the plastic nut on the 9th picture and the scheme is on the 7th)The yellow/white cable is just supply voltages +/-15V from the X and Y amps close to the front panel.Resistor from pin 3 : one goes to the ground, the other to the transistors emitters.

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: May 08, 2025, 10:14:03 pm
content: Hello Norbert67,If you would draw a schematic that matches the traces on the PCB, in order to link together all of the parts you are talking about, it would probably be useful to clarify the situation.Take also a picture from above of the PCB and add arbitrary (R1 R2 R3 C1 C3 C3 IC1...) or valid parts names to the image so that we get a coherent understanding of the board and its associated schematic. The latter must be completed with all of the parts values and power supplies.Because after 18 posts, the information we have is still too vague to be able to make valid assuptions and suggest plausible parts references for those missing transistors.It's now time to move forward in an efficient manner.

author: m k
author_rank: Super Contributor
timestamp: May 13, 2025, 12:02:56 pm
content: Quote from: Norbert67 on May 08, 2025, 07:17:08 pmWording accurate descriptions is difficult.The manual has only one +/-15V source, and one +20V.Your version with 7915 and proper ground can add -20V.But I doubt it has added a second +/-15V source, that separated twisted pair would indicate.With two different +/-15V sources the output of missing transistor pair, other than an artificial load, is also still missing.The manual has some pictures of machine internals, maybe some new photos of those pages would help something.Top left corner of manual page of 67/72 and below fuses is C504, under it are couple ICs and right from them is C505.Those capacitors seem to be axial.Are you are you got reservoir capacitor numbers right?