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Test Equipment Anonymous (TEA) group therapy thread
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Vince:

--- Quote from: bd139 on June 29, 2022, 01:11:48 pm ---Ok some quick lunch time debuggery today. I have located the 465B failure and for once it's not a tantalum capacitor. Well that's not true, there is one shorted tant but that's not what is killing the 5V rail. It's much much worse!

I eventually chased it around and found out that it only borked the power supply if channel 1 was selected. So I traced that down to the channel switch. And yep, it's a tek ASIC has gone short. But it's not an ASIC! Part is labelled Tektronix 160-0204-00 which is actually a 63S141J fuse programmable 256x4 PROM. Manual confirms this.



Fortunately it's documented!



Now the IC is available for £23 which is a bit much so I am considering what other options I can use here to replace it. The actual original blank PROM is fairly unobtainable and I'd probably fuck it up programming it.

Will mull on it for a few days...

--- End quote ---

Wow this scope is not an easy one it looks like, but it found its master it seems !  :-DD

I guess you could just use any (as old as possible) easier to get, cheap 8 bit PROM or EPROM instead, and just not use the upper 4 data bits that's all.
But that means having to make a little adapter board of course, so more work and expense... bugt more worryingly, given how compact/crammed these portable scopes are... is there sufficient space to fit an adapter board to begin with... you tell us !  >:D
Maybe instead use a more modern low profile surface mount flash or EEPROM memory, but then it means it will probably have faster rise times and maybe that will cause problems in the scope, not working at all, or introducing noise that might be problematic in the most sensitive attenuator settings ?!  :-//

Regardless, didn't know these scopes used good old lookup-table PROM trick, pretty neat... I find it cool (nice CERDIP package to boot  8) ), like floppies ! Stirring the shit again !  :-DD

bd139:
Think I might just buy the replacement. Seems less painful  :-DD

Well serendipitous thing happened. I was chucking the case back in the cupboard of doom and I hadn't looked in the pouch on it. Guess what fell out:



Yes a a spare graticule, manual and some fuses. The correct HV fuses!!! So I chucked one in and it comes up and seems to work.



The HT intensity is really jumpy because the feedback network filter capacitor has been removed (the shorted tant) but it's working.

I have capacitors arriving in the next couple of days so I will sub them in and chuck the case on and do a full retest. Once everything is confirmed mostly OK I will buy the replacement IC  :-+

At the moment channel 1 doesn't exist so I can only do limited tests.
Vince:
Ah cool, it's worth tackling the PROM issue then now, isn't it !  >:D

Ice-Tea:
Spark gap.

https://youtube.com/watch?v=tTaRLzKjoHM

https://youtube.com/watch?v=tTaRLzKjoHM

TERRA Operative:

--- Quote from: bd139 on June 29, 2022, 01:30:32 pm ---
--- Quote from: m k on June 29, 2022, 01:21:09 pm ---
--- Quote from: bd139 on June 29, 2022, 01:11:48 pm ---Ok some quick lunch time debuggery today. I have located the 465B failure and for once it's not a tantalum capacitor. Well that's not true, there is one shorted tant but that's not what is killing the 5V rail. It's much much worse!

I eventually chased it around and found out that it only borked the power supply if channel 1 was selected. So I traced that down to the channel switch. And yep, it's a tek ASIC has gone short. But it's not an ASIC! Part is labelled Tektronix 160-0204-00 which is actually a 63S141J fuse programmable 256x4 PROM. Manual confirms this.



Fortunately it's documented!



Now the IC is available for £23 which is a bit much so I am considering what other options I can use here to replace it. The actual original blank PROM is fairly unobtainable and I'd probably fuck it up programming it.

Will mull on it for a few days...

--- End quote ---

Can't you use regular 74-series stuff?

--- End quote ---

Nope - no matching parts  :-//

--- End quote ---

Ooh, maybe a microcontroller on a little adapter board?

Oh yeah, chip shortage...

Got a spare Arduino Nano clone laying around?  :-DD
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