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Thank you all for the reply. Would you plase explain why there is need to add a load to the +130V rail? I followed the schematics and it seems there is no regulation/feedback for it, so why a load is

=== Hi Roger, I looked at the schematic of Dennis Tillman load. It is for a different model and missing the load on 130V line. Minimum load currents you need on 7904 (from H?kan): -50 V: 0.08 A -15

Rogerio O ( /g/TekScopes2/topic/tek_7904_heps_operation_with/105875301 ) 02:34 #16878 ( /g/TekScopes2/message/16878 ) When I made my dummy load for the 7904 I used

I tested my dummy load after disconnecting the HV section and the HEPS went to ticking mode. However, it worked when connected to the scope. I think I have double checked all the connections, but I

==== Your suggestion would work, as an alternative pins 2&6 of P1417 should be same ground as pin 10 of P1482 (you could confirm with a DVM). Load could be between pins 2&6 and pin 3&4. You need 0.3A

It is fairly typical of the beast, but any mesh/quadrapole lens fast scope is fuzzier than, say a 547, because the beam granularity is magnified over that of a classic CRT. The thing that most don't

Thnak you all for the replies. I am lost about where to connect the load to the +5Vlamp rail. As far as I can make sense of the schematics the pin 10 of P1482 is connected to ground. According to

Chuck: Never had an issue on my 7904 for sharpness vs 7104, 2465B etc. Ozan: See alo the EEV blog on this subject and the many dummy loads for TEK scope PSU Jon

== Hi Roger, Could you clarify your question about lights common? +5VL is one of the supplies monitored by the switcher, it needs some load. You can tap lights connections at P1417 (violet colored

One thing I should mention is the 7904 on its best day has a very blurry trace. It is not as sharp as, say, a 547, or 545B. It is not as sharp as a 2465, either. The reason it is inherently blurry is

Thank you for your reply Ozan. I have measure the resistance to ground on the power rails at Z-axis boards and they were similar to the ones described on the famous article from Servicescope. From

== On 7904 LV regulator there are resistors connecting outputs to their sense inputs in case motherboard doesn't provide sense return. For example R1429 is such a resistor for +50V supply. For

Hi folks, I decided to create a new thread with with question so other (as inexperienced as I am) may benefit from the answers. While trying to find why my 7904 was showing a blurry trace, I heard a

I had one (in a piece of non-Tek gear) get red hot and glow so brightly that for an instant I thought it was a LED! Fortunately there was no collateral damage.

Hello everyone, I am selling my trusty TM503. It’s the first generation, very early 1970s, and I have modified it with the IEC line input module and it has had all 3 caps replaced with brand new

failed tants often show visible swelling, discoloration or get hot in use. There are a few on the main backplane as well. We just replace all the tants. Jon

I have a manual for "P6021 current probe and termination" free for anyone who might want it. A few stamps would be appreciated. Chuck Pilgrim

Thank you for your reply Roger. my initial focus were the “dreaded” tantalum capacitors, so I thought the resistance would be a good indication of a problem. Now that the HEPS was removed from the

Radu - 200mV is the direct input to the a/d, so doesn't go through the divider. If you want, I have a junk 501A here that has a divider on it. The other thing is the range trim pots are open frame,

Jim and all, I showered the range switches, and as much as I could reach them, also the function ones, with IPA and I seem to see some improvement. I'm going more systematically through the ranges