CG551AP - has anyone seen this problem before?


 

Oh no, not again!!! Yes apart from not getting errors 56 and 57 ...

Time to dig in yet again. Power board first given previous experience.

David

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of David C.
Partridge
Sent: 29 March 2019 14:01
To: TekScopes@groups.io; TekScopes2@groups.io
Subject: Re: [TekScopes] CG551AP - has anyone seen this problem before?

Well I hunted flaky tantalums and found no obvious ones. After re-assembly
and re-seating ROMs on CPU board, I'm now seeing the following error codes:

51, 52, 53, 54, 55 (Both Low SAC and High SAC)
56, 57 (Current mode)
81, 82, 83, 84, 85, 86, 87, 88 (All edge mode errors!)

Which is a step forward in one sense, but about 15 steps backward!

Suggestions most welcome!

Thanks
David


-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of David C.
Partridge
Sent: 29 March 2019 12:52
To: TekScopes; TekScopes2@groups.io
Subject: [TekScopes] CG551AP - has anyone seen this problem before?

I turned on my CG551AP yesterday. It flashed up the SELF TEST message in
normal brightness, then the display blanked and the only sign of life was
the LEDs just above the trigger output BNC which were dimly illuminated.

Has anyone seen this behaviour before? If so what was the problem?

I'm guessing a shorted tantalum capacitor :( ...

David


Chuck Harris <cfharris@...>
 

Yep.

There is a handful of mercury wetted relays underneath
a shield. One of the relays is probably sticking shut,
and installing a 50 ohm load all the time. This makes
the voltage output 1/2 what it should be, and trips the
error.

Also, virtually all of the transistors are plugged into
the board. Many have heatsinks. If the cables aren't
dressed properly when you install the boards, they can
push the transistors cockeyed in their sockets and then
can short to the inter board shields.

-Chuck Harris

David C. Partridge wrote:

Oh no, not again!!! Yes apart from not getting errors 56 and 57 ...

Time to dig in yet again. Power board first given previous experience.

David

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of David C.
Partridge
Sent: 29 March 2019 14:01
To: TekScopes@groups.io; TekScopes2@groups.io
Subject: Re: [TekScopes] CG551AP - has anyone seen this problem before?

Well I hunted flaky tantalums and found no obvious ones. After re-assembly
and re-seating ROMs on CPU board, I'm now seeing the following error codes:

51, 52, 53, 54, 55 (Both Low SAC and High SAC)
56, 57 (Current mode)
81, 82, 83, 84, 85, 86, 87, 88 (All edge mode errors!)

Which is a step forward in one sense, but about 15 steps backward!

Suggestions most welcome!

Thanks
David


-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of David C.
Partridge
Sent: 29 March 2019 12:52
To: TekScopes; TekScopes2@groups.io
Subject: [TekScopes] CG551AP - has anyone seen this problem before?

I turned on my CG551AP yesterday. It flashed up the SELF TEST message in
normal brightness, then the display blanked and the only sign of life was
the LEDs just above the trigger output BNC which were dimly illuminated.

Has anyone seen this behaviour before? If so what was the problem?

I'm guessing a shorted tantalum capacitor :( ...

David











 

This time the problem was fuse A5F1141 (1.5A fast) in the HV supply circuit (top left of schematic <18>). I replaced it with the same specification and it all works again.

Multiple power cycles with no problems at all.

The original fuse must have just died of old age ...

David

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Chuck Harris
Sent: 04 March 2020 04:14
To: TekScopes@groups.io
Subject: Re: [TekScopes] CG551AP - has anyone seen this problem before?

Yep.

There is a handful of mercury wetted relays underneath
a shield. One of the relays is probably sticking shut,
and installing a 50 ohm load all the time. This makes
the voltage output 1/2 what it should be, and trips the
error.

Also, virtually all of the transistors are plugged into
the board. Many have heatsinks. If the cables aren't
dressed properly when you install the boards, they can
push the transistors cockeyed in their sockets and then
can short to the inter board shields.

-Chuck Harris

David C. Partridge wrote:
Oh no, not again!!! Yes apart from not getting errors 56 and 57 ...

Time to dig in yet again. Power board first given previous experience.

David

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of David C.
Partridge
Sent: 29 March 2019 14:01
To: TekScopes@groups.io; TekScopes2@groups.io
Subject: Re: [TekScopes] CG551AP - has anyone seen this problem before?

Well I hunted flaky tantalums and found no obvious ones. After re-assembly
and re-seating ROMs on CPU board, I'm now seeing the following error codes:

51, 52, 53, 54, 55 (Both Low SAC and High SAC)
56, 57 (Current mode)
81, 82, 83, 84, 85, 86, 87, 88 (All edge mode errors!)

Which is a step forward in one sense, but about 15 steps backward!

Suggestions most welcome!

Thanks
David


-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of David C.
Partridge
Sent: 29 March 2019 12:52
To: TekScopes; TekScopes2@groups.io
Subject: [TekScopes] CG551AP - has anyone seen this problem before?

I turned on my CG551AP yesterday. It flashed up the SELF TEST message in
normal brightness, then the display blanked and the only sign of life was
the LEDs just above the trigger output BNC which were dimly illuminated.

Has anyone seen this behaviour before? If so what was the problem?

I'm guessing a shorted tantalum capacitor :( ...

David