Commodore 1901 monitor repair  - Page 1
Forum section: electronics / repair

author: Sanxion
author_rank: Contributor
timestamp: November 29, 2022, 07:43:03 am
content: Morning all,I am new to the site so I wanted first to say "hello" to you all!Issue: I am in the process of diagnosing a fault with a 35 year old monitor that I acquired recently...to give some background: I replaced the mains filter capacitor and the monitor did indeed turn on and display a correct image. However, a few days later, I switched it on and there was no activity at all. I have already been advised to replace the capacitors which I have started doing although according to my testing, the original ones seem fine. I have also observed some green "corrosion" on the switching transformer, see attached image. I am assuming it would be a good idea to replace it although I have not actually tested to see if it has failed - I am slightly hesitant to start testing the transformer whilst it is on the board and attached to the mains. I have desoldered it though to see if there is any indicator of what type/make/model it is to source a replacement. It merely has a long part number and the word Japan 1983 embossed on it.According to the schematics, the transformer outputs 24V and 114V, see attachment. I have not been able to find a replacement.What would you guys suggest I do next? I must add, I am no expert. I know how to use a soldering iron and multimeter and understand basic fault finding.

author: inse
author_rank: Super Contributor
timestamp: November 29, 2022, 08:11:52 am
content: As this is a SMPS transformer, it will be close to impossible to find a replacement for it except a salvaged one.I would advise to clean everything with a stiff brush and alcohol.Did you check for presence of 160V at the primary electrolytic (which seems to be missing in rhe photo provided) or secondary voltages already?

author: Sanxion
author_rank: Contributor
timestamp: November 29, 2022, 08:57:20 am
content: I removed the 100uF 385V capacitor and I am waiting for the new one to arrive.I will clean the transformer as suggested. I will then check for the voltages.Thanks.

author: srb1954
author_rank: Super Contributor
timestamp: November 29, 2022, 09:28:01 am
content: Quote from: Sanxion on November 29, 2022, 07:43:03 amThat brown snot used to glue down components is known to break down over time and become conductive. You should endeavour to remove all trace of it from the PCB including under any capacitors and other large components.Resistor RP16 appears to be severely burnt. I suggest you trace out other components connected to it and check for shorts before replacing it.

author: Sanxion
author_rank: Contributor
timestamp: December 13, 2022, 04:05:56 pm
content: OK...I have replaced the glue, replaced the power resistor and several capacitors - including the "big ones" : CP04, 14 & 15 - and CP10. I am pleased to say that the monitor is now working except that it is displaying in green monochrome only. I am certain however that when the monitor first switches on, the blue colors of the C64 desktop can be seen momentarily before it is replaced by green.Any ideas?

author: scroeffie
author_rank: Contributor
timestamp: April 29, 2024, 05:46:01 am
content: i have 3 of these ,first i would replace all purple caps they leak and most are out of spec .did you replace the front rifa cap they wil explodealso chek the voltage regulator .these monitors also have allot of cold solder joints reflow everything .remove all old gluechek front switch sometimes they are dirtyi just done the scart rgb mod works perfect