DuMont 1100P Oscilloscope with a Different Power Supply Board to the Manual! - Page 1
Forum section: electronics / repair

author: Chris56000
author_rank: Frequent Contributor
timestamp: August 03, 2022, 01:43:49 pm
content: Hi!I have just started work on a DuMont 1100P oscilloscope, with a number of faults as follows :–1) Green Power LED out ;2) Horizontal Deflection compressed at start and end of the scan ;3) Triggering very poor – I couldn't get it to lock even on its 600 mV Calibration Test Point ;4) Vertical Calibration way off – I get nearly 8 div. deflection with the Calibrator Signal on 1V/div !The first thing I discovered is that a totally different power supply board is fitted to my instrument, Serial No. 806021, to the one shown in both the PDF manual on Elektrotanya and the Paper 1100P Manual I bought from a UK Seller – the board shown in the manual has three MC1709G op–amps controlling three series regulators for the +15V, –15V and +100V supplies, with +5 V obtained from a plug–in switch–mode supply module referred to as A11 in the book available!The A11 Switch–mode PSU module is not fitted to my oscilloscope as the +5 V this provided now comes from the main PSU Board !The smoothing electrolytics also differ, my instrument has 1 × 850 μ @ 100 V and 3 × 4000 μ @ 30V, compared with 1 × 500 μ 200 V, 1 × 8400 μ @ 40 V and 4000 μ @ 30 V in the original circuit, and there are many other internal wiring differences as well, and I suspect the mains transformer is different as well !On my instrument, a power supply board 30669ASSY8901–7904 is fitted to the back panel, and this has 5 off 723 linear regulator ICs controlling five individual series pass transistors, and the outputs I measured were +15.02 V, –15.2 V, +61.3 V and +132.4 VCan anyone tell me if the 61.3V is correct, or should this also be +100 V?I examined the Vertical Deflection Amplifier, Horizontal Amplifier and the H.V. Generator boards and these are identical to the ones shown in my paper book, including the e.h.t. transformer.There are also three large disc ceramic capacitors and two 150 Ω carbon–composition resistors on two tagstrips connected to two thick yellow leads connected to what appears to be the 6.3 V winding of the mains transformer, also not shown in the available manual either !Can any of our US friends tell me if they've come across a DuMont 1100P with this version of the power supply I have got, and can scan the Manual for it please, if anybody has one?It would take me months to write a Manual Supplement for this instrument as there are many PCB, component and wiring differences to the Electrotanya manual and my paper book, the revised Power supply PCB would have to be traced out and all the wiring traced out and re–documented as well!Chris Williams

author: Chris56000
author_rank: Frequent Contributor
timestamp: August 03, 2022, 04:06:00 pm
content: PS!I asked Scott from Vintage Manuals W7FG and he only had the manual with the three MC1709G op–amps in the power supply plus the A11 board, the same as I've got!Artek Manuals don't list any DuMont manuals at all, BAMA only have ancient DuMont engine analyser manuals with valves (!!), k04BB have only got the 1062 user manual and circuits for the ancient 766 !Chris Williams