Drake TR-7 Repair & Restoration

 Hi,

As you may know, whilst I repair most equipment, my real specialism and passion is the repair and restoration of Drake and Collins equipment.

From early valve types right through to the last equipment made, I've spent many happy hours on customers' (and my own) equipment restoring or repairing them, and when I get offered or see such equipment to purchase then I will usually do so - depending on the price of course!

So when some Drake equipment appeared on a well know internet website for sale, I made an offer and I was pleased to be notified that it had been accepted.

It was (more or less) a complete setup with a fairly late model TR7 transceiver (1337 model - originally didn't have the DR-7 but obviously had one added later), RV-7 Remote VFO, PS-7 power supply, and a drake branded Astatic microphone. Its serial number puts it as being made in January 1980, the remote VFO serial number puts it as a similar date of manufacture with the PS-7 serial number as July 1979 - so perhaps the TR-7 and RV-7 were bought together with the PS-7 added later - or perhaps the PS-7 was just slower to sell!

All were in fairly good condition but described as non-working, the seller tested them fairly comprehensively and could resolve signals and get good TX power out of it, but no SSB audio on transmit and the digital display didn't work (displayed 51985) correctly together with the remote VFO didn't appear to function several of the aluminum discs were also missing on the main TR-7 , the VFO was 'gritty' and it was also missing a button. 

From the pictures, it looked like it had been stored somewhere dusty (garage most likely) as some of the screws on the pictures were a little rusty (!).

So deal done, and with eyes fully open (!!) I paid for it  -  it arrived safely and initial review and testing took place.

Sure enough (and somewhat unusually) the description was entirely accurate!

It did look dusty, but more importantly, it was entirely original, all the screws were original and in the right place - this is a pet hate of mine on Drake equipment especially TR-7's some screws are self tappers and some are threaded - they obviously do not go in each other's holes but some people don't realise and swap them about this causes problems with both the screws and the cases and in some cases, the only way to get the case (especially the bottom panel) is to rivet in captive bolts as the holes are so badly mangled!

Anyway, not this one, it looked like it had never had the case off (or who did carefully put things back the way they should be!

With the TR-7 I have developed a standard approach for anything that isn't 100% working (ie pretty much everything that comes through my bench!) and that is to ;

• Remove all plug-in boards and clean pins and sockets, use Deoxit (D100L) to aid cleaning of the pins, etc. and then reseat them carefully.
• Check and clean all the mini-coax interconnections - ensuring that the earth connection and the middle connection are both clean and tight - also use Deoxit in the center pin socket on the PCBs. In the TR-7 (and Ten-Tec amongst other radio) - there is no 'pin' on the coax it is just the inner connector of the coax which pushes into a small socket on the PCB connection so it is always worth checking that these are clean and the coax center is actually positioned correctly into the socket - I've had several come to me with intermittent problems that the owner has been driven mad by which were a combination of dirty coax and in two memorable incidents where the center coax was bent back and so wasn't inside the PCB connector and occasionally would make a connection !!
• Check all the controls in a similar way carefully using Dexoit to clean the potentiometers tracks where possible, together with the relevant switches, etc.
• pay special attention to the DR-7 board which has Molex connectors which 'push' down into the digital and other boards below it, in my experience simple poor or oxidized connections cause many common faults on the TR-7 series of radios.
• Clean all the switch contacts with isopropyl and then use Dexoit (D100) carefully to fully clean the contacts. I don't use the  Dexoit D5 as this has a flushing action which is great but sometimes can damage the SRBP or whatever it is.

After doing all this in around three hours - out the radio back together - and tested it, it was certainly improved with all functions working nicely - except the display which remained stubbornly at 51985, this didn't surprise me as previous experience on such a display problem showed its usually a logic/counter problem or chip failure.

I have many spares for the TR-7 series including a few DR-7 boards and so to rule out interconnections etc. I used a known good spare DR-7 board to check.

Sure enough, the display worked fine with the replacement DR-7 so that located the fault on the DR-7 board nicely! - it's worth remembering that the counter/decode circuit is quite straightforward but can be quite tricky and so without a scope its sometimes difficult to locate the problem - unless it's a connection problem of course.

In the next blog, I will cover the diagnosis and repair of this board with some tips on where and what to look for to locate the problem.