Re: DAS9100 incorrectly connected resistors on A2 power supply board


Brian
 

Hi Dan

I have just looked at my spare A2 pcb its an -02 as yours is and it looks like the same connections are made . I have not looked at the service manual or removed the heatsink plate from the back of the pcb so I assume that you are right with what you have found . I have not gone inside my DAS to check the A2 pcb yet , it is likely that I will have time for that tomorrow . If the pcb version is different and the resistor connections are also different I will let you know what I find .

On Monday, 13 April 2020, 21:45:45 BST, Dan G <dgajanovic@...> wrote:

In tracking down the cause of disconcerting hissing noises coming from the T235 transformer
of my DAS9100 A2 main power supply board, I noticed that the two 36 Ohm 2W resistors
(R360 and R362) had been installed incorrectly. They were connected to the anodes of
the two bolt-mount rectifiers CR268 and CR258, but they should have been connected to the
common cathode point. As it was, they were completely inactive since the other end of
each resistor connected via its associated capacitor back to the same starting anode point.

My A2 board is 670-6734-02, and it seems that this was not a one-off error: there is a photo
of such a board on everyone's favorite auction site which shows the same connections.
The -01 version of this board is probably not affected since neither resistor lead reaches
up to connect directly to the diodes (the connections go through the PCB).
I don't know if any -03 revision boards are affected -- I have never seen one up close.

Does anyone know if this was a known issue? My board was made in 1982. Less than a
hundred more were made before Tek rolled to the -03 revision. I've checked
all ServiceTekNotes that are available on TekWiki, but there might have been a mention in
one of the missing issues, or possibly a Wizard's Workshop article (TekWiki only seems to
have a single issue).


dan

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