[time-nuts] Help with an hp 8642a

Rob Kimberley time.bandit at btinternet.com
Thu Nov 2 08:11:24 EST 2006


Doug

I wish you luck in stripping unit down. 

The failed fan reminded me of an interesting problem I came across more
years ago than I care to remember when working on a problem with a Systron
Donner Model 5000A sweep generator. I know this is off topic, but may be of
interest to fellow Time Nuts due to the nature of the problem....

The customer (UK Spook organisation) had rejected the unit for not meeting
residual FM spec. The test data received with the unit from SD in the US
showed that the unit worked fine when shipped. Cutting a long story short
(as it took a long time to nail this problem down), we traced the problem to
the fan. The power supply used a split primary transformer which was wired
in parallel for US 115V operation (fan was 115VAC). For UK operation the two
primary windings were switched in series. The fan was however sitting on one
of the primary windings. This was causing an imbalance and taking the
residual FM out of specification. 

Replacing the fan with a 230VAC version solved the problem.

Rob Kimberley 

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Doug Millar
Sent: 01 November 2006 23:53
To: time-nuts at febo.com
Subject: [time-nuts] Help with an hp 8642a

	
  A little off topic but hope you can help. The fan quit in my HP 8642a
signal generator. Anyone have a schematic or any advise. The fan is
curiously embedded in the chassis. I think it will take a '"fan ectomy" to
get it out. Was planning to use it on the FMT. I could lay another fan over
it or just not turn it on too long.
	Doug

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