On Wed, 17 Oct 2018 17:01:33 -0700, Jeff Liebermann
wrote:

On Wed, 17 Oct 2018 20:55:22 +0100, Custos Custodum
wrote:

On Wed, 17 Oct 2018 08:00:55 -0700, Jeff Liebermann
wrote:
Much of the stuff I fix was sent
to me after some ham attempted to fix it themselves. Usually, they
won't admit it. On the repair bench right now is an Astron power
supply, an MFJ-259 antenna analyzer, two HP5300 series counters,

Which ones, if you don't mind my asking?

I'm now sure what you mean by "which ones" so I'll detail all that I
have in the queue.

1. Astron VS-35m. On arrival, it has all 4 pass transistors blown,
the 723CN regulator blown, two 1N4002 diodes shorted, and a 2N3906
shorted. That left a TIP29 transistor and an MCR225 SCR, which I've
elected to replace instead of test. I don't know what caused all the
damage but I'll confess to blowing up the 723CN regulator by plugging
it into the IC socket backwards.

2. Yet another MJF-259 to repair. I posted a web page on how to fix
these after the input bridge is blown up. It's easy to blow and
doesn't even require a transmitter. You can easily do it with just a
static discharge to the coax connector center pin.
http://www.learnbydestroying.com/jeffl/MFJ-269-repair/
The one I'm trying to repair is an early model and has the usual blown
RF shottky input diodes, with some water damage, leaky battery damage,
and the chronic crappy MFJ soldering on the ribbon cables. Note that
the needed diodes are discontinued and are becoming difficult to find.
I just ordered 100pcs on eBay.

The repair will be easy enough, but the subsequent calibration is a
real time burner. The owner has graciously offered to do the work if
he could do it at my shop as he's lacking in some of the needed test
equipment.
https://www.mfjenterprises.com/MFJ-259Bcalibration.php (not so good)
https://www.w8ji.com/mfj-259b_calibration.htm (more better)

3. There are now three counters in the queue.
One HP5300A counter with HP5302A 50MHz universal counter front end.
Two HP5300B counter with HP5308A 75MHz timer/counter front end
https://picclick.com/HEWLETT-PACKARD-MEASURING-SYSTEM-5300B-HP-50MHz-Universal-123106839896.html
I also have motley assortment of D/A, DC power, and plotter interface.
They all work except the batteries in the DC supply should be
replaced. All the counter sections seem to have the same problems.
There electrolytics in the AC supply show high ESR and all the rotary
switch contacts are tarnished. I just slopped some mineral oil and
oleic acid mix on one of the switches. The contacts look clean and
there are no more bad connections. I'll wash off the acid tomorrow so
that none of the nearby copper becomes corroded. I just ordered some
substitute electrolytics on eBay.

Looking around the shop, there's quite a bit of additional test
equipment that could use my attention. Most of it is not worth the
time but I do it anyway. For example, three sweep generators:
http://www.learnbydestroying.com/jeffl/pics/home/slides/BL-shop5.html
There also a bunch of big linear power supplies that probably need new
electrolytics. My IFR-1500 has a blown power supply that I can't seem
to fix. I thought I had it fixed in 2010, but it died again in 2015:
http://www.learnbydestroying.com/jeffl/IFR-1500%20Power%20Supply%20Repair/IFR-1500%20power%20supply%20repair.html

Does that answer your question?

Yes, thanks. I was curious about the counters as I have some
post-design experience of some of the later models in that range, but
yours were a bit before my time (mid-70s, IIRC). I might have been
able to help you out with hard-to-get parts.