TRS-80 4P broken PCB need glue recommendation

Thread Starter

Warik Yacent

Joined Apr 12, 2018
6
I just bought a TRS-80 4P and it arrived with at least 1 circuit board with 3 corners snap off taking with it some traces.
I looking for recommendation on the type of adhesive to use in a case like this. I thinking two parts epoxy something like J-B Weld or Gorilla. The board is called CRT sweep board. In the picture we see only one of the three corners to glue. 20180317_213918.jpg
 

AlbertHall

Joined Jun 4, 2014
10,258
Two part resin would be my choice, e.g. Araldite.
However if you only glue the broken edges I don't think it would be very strong. I would want to brace it a bit more with a small piece of PCB (with the copper removed) across the top of each break.
 

MisterBill2

Joined Jan 23, 2018
6,785
I would suggest using Gorilla glue, not Gorilla superglue. It does have a several hour setup time , but it is quite strong and in this application you cam leave the excess on the top side of the board and that will reinforce it. But mending the broken PCB traces can be very tedious, especially if they are coated with solder mask.
 

jpanhalt

Joined Jan 18, 2008
10,110
What is the plate it is/was mounted too? Is it metal? It seems odd to me that a board with mostly through hole components would be mounted to such a plate without standoffs and even odder if that plate is metal.

My primary concern would be determining and fixing the copper traces that you mention are also affected. Are they just grounds or are any signals? If grounds, I would be sure to re-establish good grounds. If signals, then the problem is more difficult. One approach would be to use fine (e.g., 26 to 30 awg wire, like wire-wrap wire) soldered to remaining traces to fix those circuits.

As for mounting the board, I would be concerned about using the "original" mounting without some sort of spacer and/or strain relief. (Maybe the original had spacers, and another owner removed them, which resulted in what you have.) I would seriously consider redoing that mounting. You might consider using non-conductive (e.g, balsa wood, plastic, rubber) strips with double-sided mounting tape around the edges and leaving the cosmetically ugly broken corners the way they are -- or just tape them on front and back with clear mounting tape for looks. Kapton tape might work ( EXAMPLE: https://www.ebay.com/itm/15mm-X-33m-Kapton-Tape-High-Temperature-Heat-Resistant-Polyimide/322655445554?epid=23002575193&hash=item4b1fc36232:g:O44AAOSw-GFZlARR ).
 

MisterBill2

Joined Jan 23, 2018
6,785
The concern about the mounting is quite valid. It may be that there is a cutout in the mounting plate that we don't see. Of course, it is also very possible that whoever worked on the monitor last lost the stand-off posts and just screwed the PCB right to the plate, breaking it then, not in shipping. I have seen some real disasters created by the unknowing ones. BUt it is certain that the connections must not be contacting the mounting plate.
 

jpanhalt

Joined Jan 18, 2008
10,110
After a little more thought, I think constructing slotted rails might be better than double-sided tape. A piece of insulator (wood or plastic), say 1/8" to 1/4" thick, with a 1/16" groove (run it over a thin kerf blade) could be used for mounting. Unfortunately, I do not have 3D CAD, but this image might give you the idea:

upload_2018-4-13_6-57-44.png

I would groove a long strip, then cut the triangles from it, rather than try to groove the triangles on a saw.
 

MisterBill2

Joined Jan 23, 2018
6,785
I am also suggesting that since that monitor is a CRT type that it may be a better choice to replace it with an LCD screen mounted in the same enclosure. Of course that may not be simple if this is part of an all-in-one TRS-80 .

I still think that you will need to glue the corners back on, and the Gorilla glue should stick to that kind of PCB material very well. Then glue the spacer blocks to the underside, after repairing the traces, making the blocks big enough to overlap the repaired brake. That should be very strong at that point.
 

Thread Starter

Warik Yacent

Joined Apr 12, 2018
6
Thank you for all the advise, turn out «i bought 2 parts epoxy Steel from LePage it has a high rating for fiberglass.
It was bought on eBay, and picture (below) is taken from the eBay page show the computer working, which is why I assume the damage was done during shipping, I have yet to dissemble the TRS-80 4P, I truly hope the traces repairs will be minimal (after all it's, at first look, only the corners) then a boot test then recap, retro-bright.s-l1600.jpg
 

bertus

Joined Apr 5, 2008
20,676
Hello,

I do not know the 4P, but it looks like that the high voltage is to high, as the picture looks to small on the CRT.

Bertus
 

ebp

Joined Feb 8, 2018
2,332
That board is phenolic-paper, not epoxy-glass. If you try to glue reinforcing pieces to the surface, clean the board carefully with something like 99% isopropyl alcohol first. I would typically do that with cotton swabs ("Q-tip" type), going over it at least twice with fresh swabs and alcohol. The solder side of the board may well have a lot of flux all over it. It can be removed with the same method, but you may need to make more passes to get it thoroughly clean. Alcohol is flammable, so be careful. There are more aggressive solvents that range from non-flammable to really hazardous, but some can also damage some components.

It looks to me like there is a thick insulating sheet between the circuit board and the chassis. Often boards are mounted on standoffs that are permanently attached, one way or another, to the sheet metal. Note those holding the chassis parts together. But it does look like there may be a spacer missing. Many of the parts near that corner of the board will have quite heavy longish pins.

Since the board is clearly single-sided, repair of any damaged tracks may be tedious but probably pretty simple.
 
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