Another TDS784D "rejuvenating" project --- Need advice from forum--- - Page 1
Forum section: electronics / repair

author: rodd
author_rank: Regular Contributor
timestamp: September 28, 2020, 01:23:20 pm
content: Dear all,I have been asking question in this forum about TDS 684/784 scopes and received a lot of helpful advices.Now I decided to start a "rejuvenating project" on the TDS784D, which was set aside because the CRT is very dim and out of focus.The project will consist of the following steps:1 - Replace the CRTThis will be made in two steps due to budget issues.First I will try one of those used CRTs sold at Ebay (there is one being sold for $80).From what I have read until now, I understand that I should buy the CRT AND the Yoke, since adjust the latter is a kind of "black magic" and may not work at all.Any other advice/suggestion on this step?If the scope proves to be reliable I intend to buy the LCD kit from SimmConn Labs later.2 - Replace the Dallas DS1486 & DS1650I will use the replacement kit from cuebus, not the counterfeit Chinese crap.I have already managed to make a backup of the contents of these chips using the Unified Tektool (posted on this forum by madao) and also with the floppy tool tdsNvramMinimalFloppyDumper.3- Recap the LPVS power SupplyI think this will be a good idea, but would like to hear from you if it is required.Since I will have to buy the caps from a reliable supplier (Mouser or Digikey ), I will have to wait a long time waiting for these part to arrive here with the scope disassembled, and there are kids around...If anybody has already recapped one of those and has the part list available please PM me so I could order the caps in advance.Are there any other preventive maintenance actions that are suggested?Thank you all.Roger

author: tkamiya
author_rank: Super Contributor
timestamp: September 28, 2020, 05:17:20 pm
content: Unless your current CRT is too dim to read, I wouldn't replace it with a used one. How do you know new (old) one is better? Since no one is making these anymore, chances are, it will not be that much better. LCD replacements are nice but cost is high. Since you have a nice 1GHz 4 ch scope, may be it's justifiable....I have a different approach to re-capping. Quality parts Tektronics and HP used back then lasts longer than what people think. I've removed a few and tested them. Capacity and leakage are quite acceptable - most are like new spec. So when one fails, I'd replace. But otherwise, I leave the original one in.About Dallas chip, there are new ones. (meaning freshly manufactured) Try looking at M48Z35Y and its family of chips. They are meant for Dallas replacement and they are made NEW. Once you program it, it engages battery inside. I don't know if there are types with real-time clock on it though. I've also Dremel'd and replaced battery inside. Only thing I do differently is I don't use sockets and coin cells. There are leaded types and they seem to have much better longevity spec. I'm sorry, I don't have part numbers handy but Digikey carries many. I certainly won't buy from eBay. Because of demand, there are so many fakes and new OLD stocks.

author: madao
author_rank: Frequent Contributor
timestamp: December 04, 2020, 01:56:57 pm
content: dim color CRT is common problem. You can searching after good CRT, if you want paid $300++$80 CRT is high risk.Other cheap solution: overheating of dim color CRTMy tip: TDS544A has same color CRT and eletronic, schematic exisits. CRT heater is connect over resistor to 24V PSU. Solution: Adding 120-150 ohm on this resistor, CRT heater voltage rise from 12-13 up to 18 V, it is useable and focus is better, on cost shorter lifetime. Long stable solution: use simmconn TFT kit or thinking with 6.5" TFT VGA Display.End statium: you can use him, if room is dark.To dim.... despite intensity = 100% and trimpot of intensity is on point, which focus got bad.Other case: very good color CRT. (here 65% Intensity )