[Heathkit] Dumb speaker question

[Singley, Rodger]

Bob,

If you want a really bad manual, try an Icom IC-751 as an example.  I just got through repairing one where the only problem was you had to use the external receive terminal for the receiver to work.  It appeared that it should be a simple repair and probably had an issue with the reed relay (or its driver) that connects the receiver to the main coax fitting.

Fast forward to the IC-751 service manual that came with the rig.  It had such interesting mistakes as showing the reed relay COIL connected to the transmitter RF output, minimal provision of expected voltages and several of them obviously incorrect including showing significantly different voltages at different points on the same copper trace, and an excruciating detailed discussion of many of the circuits but very little about the T/R circuitry which is what I needed.  After 3 hours of manual and bench time I traced the problem to a leaky transistor many stages away that was preventing the relay driver from receiving the proper voltage.  One 85 cent transistor later and it operates as it should.

At the opposite end of the spectrum are Tektronix manuals which are extremely user friendly and helpful.  The Heath manuals aren't on the same plane as Tektronix but I have no complaints about them.

Rodger WQ9E


-----Original Message-----
From: heathkit-bounces at mailman.qth.net on behalf of rbethman
Sent: Sun 2/28/2010 4:31 PM
To: Heathkit at mailman.qth.net
Cc: Jim Shorney
Subject: Re: [Heathkit] Dumb speaker question
 

I just looked at my big TX-1 (1960) and my big HW-101 schematics.

They have VERY few voltage points, and quite frankly, they are small 
enough that even with my bifocals, the points are hard to read, and VERY 
sparse!

While I would in principal, agree to this philosophy, it would better be 
done on a Hallicrafters or Hammarlund.

Since we ARE talking Heathkit, we have a horse of a different color!

Bob - N0DGN

On 2/28/2010 4:36 PM, Jim Shorney wrote:
> <snip>
> If you have the manual, go though the rig and take voltage readings and
> complare them with values that the manual expects. This can be your first clue
> to where you need to look at resistor values. I find it convenient to lay out
> the manual values on a spreadsheet and print it out, this provides a handy
> chart for recording measured values and complaring to expected readings.
>
> Power resistors (carbon comp. 1 watt, 2 watt, and higher) are the first to look
> at. Then, any smaller ones that show visible signs of heat stress. Look at the
> schematic, it will show you which ones are "isolated" by their role in the
> circuit and can be measured without desoldering one end.
>
> 73
>
> -Jim
<snip>
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