ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
i still regret that my brains did allow me in high school and later in university to obtain ample knowledge of electronics and so keeping me away from easy ways to solve problems in faulty audio devices.
Consequently I have to address questions for help to forums like Beoworld's .
So here is one:One of recently obtained beauties is a BM 1700 unveiling the usual problems with the tone- and bandselection sliders; I was very lucky to obtain, via the internet, replacements in impeccable state for these panels. After installing, the biggest problem was solved, but this action made audible that the balance was not yet OK. Inspection showed the situation on the powertrap; see picture. Measuring these 2 R's (0.39ohm should show on the multimeter, but they did not : one was short.
Inevitable question is: except replacing these 2 R's what other components that could have died and should be removed to be tested outside the pc board ( or maybe onboard)
Ideally all components in the affected output channel.But as a minimum the two output stage darlington transistors and any other semiconductors working closely together with them, the idle current trimmer and of course the two emitter resistors and any other components looking dodgy.
In the photo is seem the darlington is not fitted to the cooling fin. I suppose you did that to take it out and diagnose?
If you want the easy solution - go here:https://beoparts.com/2016/12/24/beomaster-1600-1700-stereo-power-amplifier-8002378/
Martin
(in the first line of my post I omitted the word 'not'' in front of 'allow')
Yes I took out the metal cooling plates.
The first problem now is that searcning the internet for the TE1088 and TE1089 darlingtons I get sofar zero results, can you recomment equivalents or is the only option to make a bid on the item accessed via the link in your reply? ( what would be a reasonable bid then?)Aad
TE1088 and TE1089 here:
https://beoparts.com/category/semiconductors/transistors/
PM or email me.
As follow up to our email conversation with subject testing the TE1088/9 darlingtons I show here the result of the tests.
Needles to say that it is a reassuring picture, right?
Aad
Sorry for the highway-sized photo; I do not know how to upload a small sized picture.
That is BAD. Replace them.
What do you mean: the transistors (what should the measurement look like?)
or the photo?Aad
I appears now that I cheered to early: I did some comparative testing vs the ones that are in the right channel and I learned what the good ones should look now on the display. Also the spare ones that I found are all 4 faulty.
Therefore I wonder if the BD901 and BD902 or BDX33A and BDX34 could be used as equivalents for replacing the obsolete and very rare TE1088/9's , because these seem to be available in the market?If so would that require adjustments and/or replacements to surrounding components?
Awaiting the new transistors (the BD's and BDX's) I wonder if I also should buy new "reservoir"caps ( I am replacing some components already}, because on the picture it looks like the beginning of the end, they measure 5393 uF and 6119 uF; I have spare one of 6139 uF. They should be around 4700 uF.
In case of buying new one, will the available 60V caps be a good alternative in stead of the present 50V ones ?
Aad Jansse:will the available 60V caps be a good alternative in stead of the present 50V ones
Will be ok.
I agree.Though they are not reservoir capacitors but output series caps.
(Another filling up the gap in my knowledge, as I referred to in the first line of my first post of this thread)
I am back at where I was at the beginning of this thread and even worse:
I finally acquired the necessary parts that had to replace the ( possibly) faulty ones. To make a long story short: a headphone connected, I had the nerve to press the P1 (preset FM) key: For short a moment “l’histoire se répète”, as the French say: only one channel came to life, then I switched it off.
Then I connected one small speaker in order to find out if either the left channel or the right one was the problem, powered the 1700 on again and there was a short hum and everything went dead, no smoke. Quite frustrating! Unfortunately there are no fuses that can be blamed and I keep my fingers crossed when I am going to investigate the condition of the rare TE-darlingtons in the powerstage and subsequently check the other components.
Did you set the idle currents, before you connected speakers?
I hardly dare to confess: NO!!; In my eagerness to hear the result of my work I forgot this and I am now punished by facing the situation that the result is dramatically negative!!
But, wise men used to say: all comes with experience ( learning by doing): Impatience is never a good argument for anything.
Is all lost now? Is there any hope that the TE-darlington IC's survived the shockwave?
Anyway I have to start from scratch with equivalent type transistors; e.g. the BD33/34?
You set the idle current with no speakers attached.Start with the trimmers in center position and power the Beomaster up on a variac while monitoring the idle currents.
So I am going now on a quest to find someone with a variac. Meanwhile I would appreciate hearing an answer on my question about the use of the BD33 and BD34 as substitutes for the now faulty TE 1088 and TE1089.